{-| Copyright : © 2014-2016, Christiaan Baaij, 2017-2019, Myrtle Software Ltd 2017 , QBayLogic, Google Inc., 2021-2023, QBayLogic B.V. 2022 , LUMI GUIDE FIETSDETECTIE B.V. Licence : Creative Commons 4.0 (CC BY 4.0) (https://creativecommons.org/licenses/by/4.0/) Maintainer: QBayLogic B.V. <devops@qbaylogic.com> -} {-# LANGUAGE NoImplicitPrelude #-} {-# OPTIONS_GHC -fno-warn-unused-imports #-} module Clash.Tutorial ( -- * Introduction -- $introduction -- * Install Clash -- $installation -- * Working with this tutorial -- $working -- * Your first circuit -- $mac_example -- *** Sequential circuit -- $mac2 -- *** Generating VHDL -- $mac3 -- *** Circuit testbench -- $mac4 -- *** Generating Verilog and SystemVerilog -- $mac5 -- *** Alternative specifications -- $mac6 -- * Higher-order functions -- $higher_order -- * Composition of sequential circuits -- $composition_sequential -- * Synthesize annotations: controlling the VHDL\/(System)Verilog generation. -- $annotations -- * Multiple clock domains -- $multiclock -- * Advanced: Primitives -- $primitives -- *** Verilog primitives -- $vprimitives -- *** SystemVerilog primitives -- $svprimitives -- * Conclusion -- $conclusion -- * Troubleshooting -- $errorsandsolutions -- * Limitations of Clash -- $limitations -- * Clash vs Lava -- $vslava -- * Migration guide from Clash 0.99 -- $migration ) where import Clash.Prelude import Clash.Explicit.Testbench import Clash.XException (NFDataX) import Control.Monad.ST import Data.Array import Data.Char import Data.Int import GHC.Prim import GHC.TypeLits import GHC.Word import GHC.Stack import Data.Default.Class {- $setup >>> :set -XTemplateHaskell -XDataKinds -XConstraintKinds -XTypeApplications >>> :m -Prelude >>> import Clash.Prelude >>> import Clash.Explicit.Testbench >>> :{ let ma :: Num a => a -> (a, a) -> a ma acc (x,y) = acc + x * y :} >>> :{ let macT :: Num a => a -> (a,a) -> (a,a) macT acc (x,y) = (acc',o) where acc' = ma acc (x,y) o = acc :} >>> :set -XFlexibleContexts >>> :set -fplugin GHC.TypeLits.Normalise >>> let compareSwapL a b = if a < b then (a,b) else (b,a) >>> :{ let sortV xs = map fst sorted :< (snd (last sorted)) where lefts = head xs :> map snd (init sorted) rights = tail xs sorted = zipWith compareSwapL lefts rights :} >>> :{ let sortVL xs = map fst sorted :< (snd (last sorted)) where lefts = head xs :> map snd (init sorted) rights = tail xs sorted = zipWith compareSwapL (lazyV lefts) rights :} >>> let mac = mealy macT 0 >>> :{ let topEntity :: Clock System -> Reset System -> Enable System -> Signal System (Signed 9, Signed 9) -> Signal System (Signed 9) topEntity = exposeClockResetEnable mac :} >>> :{ let testBench :: Signal System Bool testBench = done where testInput = stimuliGenerator clk rst $(listToVecTH [(1,1) :: (Signed 9,Signed 9),(2,2),(3,3),(4,4)]) expectedOutput = outputVerifier' clk rst $(listToVecTH [0 :: Signed 9,1,5,14,14,14,14]) done = expectedOutput (topEntity clk rst enableGen testInput) clk = tbSystemClockGen (not <$> done) rst = systemResetGen :} >>> :{ let fibR :: Unsigned 64 -> Unsigned 64 fibR 0 = 0 fibR 1 = 1 fibR n = fibR (n-1) + fibR (n-2) :} >>> :{ let fibS :: SystemClockResetEnable => Signal System (Unsigned 64) fibS = r where r = register 0 r + register 0 (register 1 r) :} -} {- $introduction Clash is a functional hardware description language that borrows both its syntax and semantics from the functional programming language Haskell. It provides a familiar structural design approach to both combination and synchronous sequential circuits. The Clash compiler transforms these high-level descriptions to low-level synthesizable VHDL, Verilog, or SystemVerilog. Features of Clash: * Strongly typed, but with a very high degree of type inference, enabling both safe and fast prototyping using concise descriptions. * Interactive REPL: load your designs in an interpreter and easily test all your component without needing to setup a test bench. * Compile your designs for fast simulation. * Higher-order functions, in combination with type inference, result in designs that are fully parametric by default. * Synchronous sequential circuit design based on streams of values, called @Signal@s, lead to natural descriptions of feedback loops. * Multiple clock domains, with type safe clock domain crossing. * Template language for introducing new VHDL/(System)Verilog primitives. Although we say that Clash borrows the semantics of Haskell, that statement should be taken with a grain of salt. What we mean to say is that the Clash compiler views a circuit description as /structural/ description. This means, in an academic handwavy way, that every function denotes a component and every function application denotes an instantiation of said component. Now, this has consequences on how we view /recursively/ defined functions: structurally, a recursively defined function would denote an /infinitely/ deep / structured component, something that cannot be turned into an actual circuit (See also <#limitations Limitations of Clash>). On the other hand, Haskell's by-default non-strict evaluation works very well for the simulation of the feedback loops, which are ubiquitous in digital circuits. That is, when we take our structural view to circuit descriptions, value-recursion corresponds directly to a feedback loop: @ counter = s where s = 'register' 0 (s + 1) @ The above definition, which uses value-recursion, /can/ be synthesized to a circuit by the Clash compiler. Over time, you will get a better feeling for the consequences of taking a /structural/ view on circuit descriptions. What is always important to remember is that every applied functions results in an instantiated component, and also that the compiler will /never/ infer / invent more logic than what is specified in the circuit description. With that out of the way, let us continue with installing Clash and building our first circuit. -} {- $installation For installation instructions, see <https://clash-lang.org/install/ clash-lang.org/install/>. -} {- $working This tutorial can be followed best whilst having the Clash interpreter running at the same time. If you followed the installation instructions based on <https://docs.haskellstack.org/en/stable/README/#how-to-install Stack>, you can start the Clash compiler in interpretive mode by: @ stack exec --resolver lts-19 --package clash-ghc -- clashi @ If instead you followed the [instructions](https://clash-lang.org/install/linux/) to setup a starter project with Stack, you can also run @clashi@ inside such a project. Change to the directory of the project, and invoke @ stack run -- clashi @ If you instead set up the starter project with GHC and Cabal, change to the directory of the project and invoke @ cabal run -- clashi @ For those familiar with Haskell/GHC, this is indeed just @GHCi@, with three added commands (@:vhdl@, @:verilog@, and @:systemverilog@). You can load files into the interpreter using the @:l \<FILENAME\>@ command. Now, depending on your choice in editor, the following @edit-load-run@ cycle probably work best for you: * __Commandline (e.g. emacs, vim):__ * You can run system commands using @:!@, for example @:! touch \<FILENAME\>@ * Set the /editor/ mode to your favourite editor using: @:set editor \<EDITOR\>@ * You can load files using @:l@ as noted above. * You can go into /editor/ mode using: @:e@ * Leave the editor mode by quitting the editor (e.g. @:wq@ in @vim@) * __GUI (e.g. SublimeText, Notepad++):__ * Just create new files in your editor. * Load the files using @:l@ as noted above. * Once a file has been edited and saved, type @:r@ to reload the files in the interpreter You are of course free to deviate from these suggestions as you see fit :-). It is just recommended that you have the Clash interpreter open during this tutorial. -} {- $mac_example The very first circuit that we will build is the \"classic\" multiply-and-accumulate (MAC) circuit. This circuit is as simple as it sounds, it multiplies its inputs and accumulates them. Before we describe any logic, we must first create the file we will be working on and input some preliminaries: * Create the file: @ MAC.hs @ * Write on the first line the module header: @ module MAC where @ Module names must always start with a __C__apital letter. Also make sure that the file name corresponds to the module name. * Add the import statement for the Clash prelude library: @ import Clash.Prelude @ This imports all the necessary functions and datatypes for circuit description. We can now finally start describing the logic of our circuit, starting with just the multiplication and addition: @ ma acc (x, y) = acc + x * y @ The circuit we just wrote is a combinational circuit: no registers are inserted (you describe explicitly where Clash will insert registers, as we'll later see). We usually refer to circuits as /functions/, similar to programming languages such as C, Python, or Haskell. In this case, the function we just defined is called @ma@. Its first argument is @acc@, its second is @(x, y)@ - a composite type called a tuple. This component is "unpacked", and its first element is called @x@, its second @y@. Everything to the right of the equals symbol is @ma@'s result. If you followed the instructions of running the interpreter side-by-side, you can already test this function: >>> ma 4 (8, 9) 76 >>> ma 2 (3, 4) 14 We can also examine the inferred type of @ma@ in the interpreter: >>> :t ma ma :: Num a => a -> (a, a) -> a You should read this as follows: * __@ma ::@__, @ma@ is of type.. * __@Num a@__, there is some type called @a@ that is a @'Num'@. Examples of instances of @'Num'@ are @'Int'@, @'Signed' 16@, @'Index' 32@, and @'Float'@. * __@a@__, @ma@'s first argument is of type @a@ * __@(a, a)@__, @ma@'s second argument is of type @(a, a)@ * __@a@__, @ma@'s result is of type @a@ Note that @ma@ therefore works on multiple types! The only condition we imposed is that @a@ should be a @'Num'@ber type. In Clash this means it should support the operations @'Prelude.+'@, @'Prelude.-'@, @'Prelude.*'@, and some others. Indeed, this is why Clash adds the constraint in the first place: the definition of @ma@ uses @+@ and @*@. Whenever a function works over multiple types, we call it /polymorphic/ ("poly" meaning "many", "morphic" meaning "forms"). While powerful, its not clear how Clash should synthesize this as numbers come in a great variety in (bit)sizes. We will later see how to use this function in a /monomorphic/ manner. Talking about /types/ also brings us to one of the most important parts of this tutorial: /types/ and /synchronous sequential logic/. Especially how we can always determine, through the types of a specification, if it describes combinational logic or (synchronous) sequential logic. We do this by examining the definition of one of the sequential primitives, the @'register'@ function: @ register ( 'HiddenClockResetEnable' dom , 'Clash.XException.NFDataX' a ) => a -> 'Signal' dom a -> 'Signal' dom a register i s = ... @ Where we see that the second argument and the result are not just of the /polymorphic/ @a@ type, but of the type: @'Signal' dom a@. All (synchronous) sequential circuits work on values of type @'Signal' dom a@. Combinational circuits always work on values of, well, not of type @'Signal' dom a@. A 'Signal' is an (infinite) list of samples, where the samples correspond to the values of the 'Signal' at discrete, consecutive, ticks of the /clock/. All (sequential) components in the circuit are synchronized to this global /clock/. For the rest of this tutorial, and probably at any moment where you will be working with Clash, you should probably not actively think about 'Signal's as infinite lists of samples, but just as values that are manipulated by sequential circuits. To make this even easier, it actually not possible to manipulate the underlying representation directly: you can only modify 'Signal' values through a set of primitives such as the 'register' function above. Now, let us get back to the functionality of the 'register' function: it is a simple <https://en.wikipedia.org/wiki/Flip-flop_(electronics) latch> that only changes state at the tick of the global /clock/, and it has an initial value @a@ which is its output at time 0. We can further examine the 'register' function by taking a look at the first 4 samples of the 'register' functions applied to a constant signal with the value 8: >>> sampleN @System 4 (register 0 (pure (8 :: Signed 8))) [0,0,8,8] Where we see that the initial value of the signal is the specified 0 value, followed by 8's. You might be surprised to see /two/ zeros instead of just a single zero. What happens is that in Clash you get to see the output of the circuit /before/ the clock becomes actives. In other words, in Clash you get to describe the powerup values of registers too. Whether this is a defined or unknown value depends on your hardware target, and can be configured by using a different synthesis @'Domain'@. The default synthesis domain, @'System', assumes that registers do have a powerup value - as is true for most FPGA platforms in most contexts. -} {- $mac2 The 'register' function is our primary sequential building block to capture /state/. It is used internally by one of the "Clash.Prelude" function that we will use to describe our MAC circuit. Note that the following paragraphs will only show one of many ways to specify a sequential circuit, in the section <#mac6 Alternative specifications> we will show a couple more. A principled way to describe a sequential circuit is to use one of the classic machine models, within the Clash prelude library offer standard function to support the <http://en.wikipedia.org/wiki/Mealy_machine Mealy machine>. To improve sharing, we will combine the transition function and output function into one. This gives rise to the following Mealy specification of the MAC circuit: @ macT acc (x, y) = (acc', o) where acc' = ma acc (x, y) o = acc @ Note that the @where@ clause and explicit tuple are just for demonstrative purposes, without loss of sharing we could've also written: @ macT acc inp = (ma acc inp, acc) @ Going back to the original specification we note the following: * @acc@ is the current /state/ of the circuit. * @(x, y)@ is its input. * @acc'@ is the updated, or next, /state/. * @o@ is the output. When we examine the type of @macT@ we see that is still completely combinational: >>> :t macT macT :: Num a => a -> (a, a) -> (a, a) The "Clash.Prelude" library contains a function that creates a sequential circuit from a combinational circuit that has the same Mealy machine type / shape of @macT@: @ mealy :: ('HiddenClockResetEnable' dom, 'Clash.XException.NFDataX' s) => (s -> i -> (s,o)) -> s -> ('Signal' dom i -> 'Signal' dom o) mealy f initS = ... @ The complete sequential MAC circuit can now be specified as: @ mac inp = 'mealy' macT 0 inp @ Where the first argument of @'mealy'@ is our @macT@ function, and the second argument is the initial state, in this case 0. We can see it is functioning correctly in our interpreter: >>> import qualified Data.List as L >>> L.take 4 $ simulate @System mac [(1,1),(2,2),(3,3),(4,4)] [0,1,5,14] Where we simulate our sequential circuit over a list of input samples and take the first 4 output samples. We have now completed our first sequential circuit and have made an initial confirmation that it is working as expected. -} {- $mac3 We are now almost at the point that we can create actual hardware, in the form of a <http://en.wikipedia.org/wiki/VHDL VHDL> netlist, from our sequential circuit specification. The first thing we have to do is create a function called @topEntity@ and ensure that it has a __monomorphic__ type. In our case that means that we have to give it an explicit type annotation. It might not always be needed, you can always check the type with the @:t@ command and see if the function is monomorphic: @ topEntity :: 'Clock' 'System' -> 'Reset' 'System' -> 'Enable' 'System' -> 'Signal' 'System' ('Signed' 9, 'Signed' 9) -> 'Signal' 'System' ('Signed' 9) topEntity = 'exposeClockResetEnable' mac @ Which makes our circuit work on 9-bit signed integers. Including the above definition, our complete @MAC.hs@ should now have the following content: @ module MAC where import "Clash.Prelude" ma acc (x,y) = acc + x * y macT acc (x,y) = (acc',o) where acc' = ma acc (x,y) o = acc mac inp = 'mealy' macT 0 inp topEntity :: 'Clock' 'System' -> 'Reset' 'System' -> 'Enable' 'System' -> 'Signal' 'System' ('Signed' 9, 'Signed' 9) -> 'Signal' 'System' ('Signed' 9) topEntity = 'exposeClockResetEnable' mac @ The @topEntity@ function is the starting point for the Clash compiler to transform your circuit description into a VHDL netlist. It must meet the following restrictions in order for the Clash compiler to work: * It must be completely monomorphic * It must be completely first-order * Although not strictly necessary, it is recommended to /expose/ 'Hidden' clock and reset arguments, as it makes user-controlled <Clash-Tutorial.html#annotations name assignment> in the generated HDL easier to do. Our @topEntity@ meets those restrictions, and so we can convert it successfully to VHDL by executing the @:vhdl@ command in the interpreter. This will create a directory called @vhdl@, which contains a directory called @MAC@, which ultimately contains all the generated VHDL files. You can now load these files into your favourite VHDL synthesis tool, marking @topentity.vhdl@ as the file containing the top level entity. -} {- $mac4 There are multiple reasons as to why you might want to create a so-called /test bench/ for the generated HDL: * You want to compare post-synthesis / post-place&route behavior to that of the behavior of the original generated HDL. * Need representative stimuli for your dynamic power calculations. * Verify that the HDL output of the Clash compiler has the same behavior as the Haskell / Clash specification. For these purposes, you can have the Clash compiler generate a /test bench/. In order for the Clash compiler to do this you need to do one of the following: * Create a function called /testBench/ in the root module. * Annotate your /topEntity/ function (or function with a <Clash-Tutorial.html#g:12 Synthesize> annotation) with a 'TestBench' annotation. For example, you can test the earlier defined /topEntity/ by: @ import "Clash.Explicit.Testbench" topEntity :: 'Clock' System -> 'Reset' System -> 'Enable' System -> 'Signal' System ('Signed' 9, 'Signed' 9) -> 'Signal' System ('Signed' 9) topEntity = 'exposeClockResetEnable' mac testBench :: 'Signal' System Bool testBench = done where testInput = 'stimuliGenerator' clk rst $('listToVecTH' [(1,1) :: ('Signed' 9,'Signed' 9),(2,2),(3,3),(4,4)]) expectOutput = 'outputVerifier'' clk rst $('listToVecTH' [0 :: 'Signed' 9,1,5,14,14,14,14]) done = expectOutput (topEntity clk rst en testInput) en = 'enableGen' clk = 'tbSystemClockGen' (not '<$>' done) rst = 'systemResetGen' @ This will create a stimulus generator that creates the same inputs as we used earlier for the simulation of the circuit, and creates an output verifier that compares against the results we got from our earlier simulation. We can even simulate the behavior of the /testBench/: >>> sampleN 8 testBench [False,False,False,False,False cycle(<Clock: System>): 5, outputVerifier expected value: 14, not equal to actual value: 30 ,False cycle(<Clock: System>): 6, outputVerifier expected value: 14, not equal to actual value: 46 ,False cycle(<Clock: System>): 7, outputVerifier expected value: 14, not equal to actual value: 62 ,False] We can see that for the first 4 samples, everything is working as expected, after which warnings are being reported. The reason is that 'stimuliGenerator' will keep on producing the last sample, (4,4), while the 'outputVerifier'' will keep on expecting the last sample, 14. In the VHDL testbench these errors won't show, as the global clock will be stopped after 4 ticks. You should now again run @:vhdl@ in the interpreter; this time the compiler will take a bit longer to generate all the circuits. Inside the @.\/vhdl\/MAC@ directory you will now also find a /testbench/ subdirectory containing all the @vhdl@ files for the /test bench/. After compilation is finished you load all the files in your favourite VHDL simulation tool. Once all files are loaded into the VHDL simulator, run the simulation on the @testbench@ entity. On questasim / modelsim: doing a @run -all@ will finish once the output verifier will assert its output to @true@. The generated testbench, modulo the clock signal generator(s), is completely synthesizable. This means that if you want to test your circuit on an FPGA, you will only have to replace the clock signal generator(s) by actual clock sources, such as an onboard PLL. -} {- $mac5 Aside from being able to generate VHDL, the Clash compiler can also generate Verilog and SystemVerilog. You can repeat the previous two parts of the tutorial, but instead of executing the @:vhdl@ command, you execute the @:verilog@ or @:sytemverilog@ command in the interpreter. This will create a directory called @verilog@, respectively @systemverilog@, which contains a directory called @MAC@, which ultimately contains all the generated Verilog and SystemVerilog files. Verilog files end in the file extension @v@, while SystemVerilog files end in the file extension @sv@. This concludes the main part of this section on \"Your first circuit\", read on for alternative specifications for the same @mac@ circuit, or just skip to the next section where we will describe another DSP classic: an FIR filter structure. -} {- $mac6 #mac6# * __'Num' instance for 'Signal'__: @'Signal' a@ is also also considered a 'Num'eric type as long as the value type /a/ is also 'Num'eric. This means that we can also use the standard numeric operators, such as ('GHC.Num.*') and ('GHC.Num.+'), directly on signals. An alternative specification of the @mac@ circuit will also use the 'register' function directly: @ macN (x,y) = acc where acc = 'register' 0 (acc + x * y) @ * __'Applicative' instance for 'Signal'__: We can also mix the combinational @ma@ function, with the sequential 'register' function, by lifting the @ma@ function to the sequential 'Signal' domain using the operators ('<$>' and '<*>') of the 'Applicative' type class: @ macA (x,y) = acc where acc = 'register' 0 acc' acc' = ma '<$>' acc '<*>' 'bundle' (x,y) @ * __'Control.Monad.State.Lazy.State' Monad__ We can also implement the original @macT@ function as a @'Control.Monad.State.Lazy.State'@ monadic computation. First we must add an extra import statement, right after the import of "Clash.Prelude": @ import Control.Monad.State @ We can then implement macT as follows: @ macTS (x,y) = do acc <- 'Control.Monad.State.Lazy.get' 'Control.Monad.State.Lazy.put' (acc + x * y) return acc @ We can use the 'mealy' function again, although we will have to change position of the arguments and result: @ asStateM :: ( 'HiddenClockResetEnable' dom , 'NFDataX' s ) => (i -> 'Control.Monad.State.Lazy.State' s o) -> s -> ('Signal' dom i -> 'Signal' dom o) asStateM f i = 'mealy' g i where g s x = let (o,s') = 'Control.Monad.State.Lazy.runState' (f x) s in (s',o) @ We can then create the complete @mac@ circuit as: @ macS = asStateM macTS 0 @ -} {- $higher_order An FIR filter is defined as: the dot-product of a set of filter coefficients and a window over the input, where the size of the window matches the number of coefficients. @ dotp as bs = 'sum' ('zipWith' (*) as bs) fir coeffs x_t = y_t where y_t = dotp coeffs xs xs = 'window' x_t topEntity :: 'Clock' 'System' -> 'Reset' 'System' -> 'Enable' 'System' -> 'Signal' 'System' ('Signed' 16) -> 'Signal' 'System' ('Signed' 16) topEntity = exposeClockResetEnable (fir (0 ':>' 1 ':>' 2 ':>' 3 ':>' 'Nil')) @ Here we can see that, although the Clash compiler handles recursive function definitions poorly, many of the regular patterns that we often encounter in circuit design are already captured by the higher-order functions that are present for the 'Vec'tor type. -} {- $composition_sequential Given a function @f@ of type: @ __f__ :: Int -> (Bool, Int) -> (Int, (Int, Bool)) @ When we want to make compositions of @f@ in @g@ using 'mealy', we have to write: @ g a b c = (b1,b2,i2) where (i1,b1) = 'unbundle' ('mealy' f 0 ('bundle' (a,b))) (i2,b2) = 'unbundle' ('mealy' f 3 ('bundle' (c,i1))) @ Why do we need these 'bundle', and 'unbundle' functions you might ask? When we look at the type of 'mealy': @ __mealy__ :: HiddenClockResetEnable dom => (s -> i -> (s,o)) -> s -> ('Signal' dom i -> 'Signal' dom o) @ we see that the resulting function has an input of type @'Signal' dom i@, and an output of @'Signal' dom o@. However, the type of @(a,b)@ in the definition of @g@ is: @('Signal' dom Bool, 'Signal' dom Int)@. And the type of @(i1,b1)@ is of type @('Signal' dom Int, 'Signal' dom Bool)@. Syntactically, @'Signal' dom (Bool,Int)@ and @('Signal' dom Bool, 'Signal' dom Int)@ are /unequal/. So we need to make a conversion between the two, that is what 'bundle' and 'unbundle' are for. In the above case 'bundle' gets the type: @ __bundle__ :: ('Signal' dom Bool, 'Signal' dom Int) -> 'Signal' dom (Bool,Int) @ and 'unbundle': @ __unbundle__ :: 'Signal' dom (Int,Bool) -> ('Signal' dom Int, 'Signal' dom Bool) @ The /true/ types of these two functions are, however: @ __bundle__ :: 'Bundle' a => 'Unbundled' dom a -> 'Signal' dom a __unbundle__ :: 'Bundle' a => 'Signal' dom a -> 'Unbundled' dom a @ 'Unbundled' is an <https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#associated-data-and-type-families associated type family> belonging to the 'Bundle' <http://en.wikipedia.org/wiki/Type_class type class>, which, together with 'bundle' and 'unbundle' defines the isomorphism between a product type of 'Signal's and a 'Signal' of a product type. That is, while @('Signal' dom a, 'Signal' dom b)@ and @'Signal' dom (a,b)@ are not equal, they are /isomorphic/ and can be converted from, or to, the other using 'bundle' and 'unbundle'. Instances of this 'Bundle' type-class are defined as /isomorphisms/ for: * All tuples up to and including 62-tuples (GHC limit) * The 'Vec'tor type But they are defined as /identities/ for: * All elementary / primitive types such as: 'Bit', 'Bool', @'Signed' n@, etc. That is: @ instance 'Bundle' (a,b) where type 'Unbundled' dom (a,b) = ('Signal' dom a, 'Signal' dom b) bundle (a,b) = (,) '<$>' a '<*>' b unbundle tup = (fst '<$>' tup, snd '<*>' tup) @ but, @ instance 'Bundle' Bool where type 'Unbundled' dom Bool = 'Signal' dom Bool bundle s = s unbundle s = s @ What you need take away from the above is that a product type (e.g. a tuple) of 'Signal's is not syntactically equal to a 'Signal' of a product type, but that the functions of the 'Bundle' type class allow easy conversion between the two. As a final note on this section we also want to mention the 'mealyB' function, which does the bundling and unbundling for us: @ mealyB :: ('Bundle' i, 'Bundle' o) => (s -> i -> (s,o)) -> s -> 'Unbundled' dom i -> 'Unbundled' dom o @ Using 'mealyB' we can define @g@ as: @ g a b c = (b1,b2,i2) where (i1,b1) = 'mealyB' f 0 (a,b) (i2,b2) = 'mealyB' f 3 (c,i1) @ The general rule of thumb is: always use 'mealy', unless you do pattern matching or construction of product types, then use 'mealyB'. -} {- $annotations #annotations# 'Synthesize' annotations allow us to control hierarchy and naming aspects of the Clash compiler, specifically, they allow us to: * Assign names to entities (VHDL) \/ modules ((System)Verilog), and their ports. * Put generated HDL files of a logical (sub)entity in their own directory. * Use cached versions of generated HDL, i.e., prevent recompilation of (sub)entities that have not changed since the last run. Caching is based on a @.manifest@ which is generated alongside the HDL; deleting this file means deleting the cache; changing this file will result in /undefined/ behavior. Functions with a 'Synthesize' annotation must adhere to the following restrictions: * Although functions with a 'Synthesize' annotation can of course depend on functions with another 'Synthesize' annotation, they must not be mutually recursive. * Functions with a 'Synthesize' annotation must be completely /monomorphic/ and /first-order/, and cannot have any /non-representable/ arguments or result. Also take the following into account when using 'Synthesize' annotations. * The Clash compiler is based on the GHC Haskell compiler, and the GHC machinery does not understand 'Synthesize' annotations and it might subsequently decide to inline those functions. You should therefor also add a @{\-\# NOINLINE f \#-\}@ pragma to the functions which you give a 'Synthesize' functions. * Functions with a 'Synthesize' annotation will not be specialized on constants. Finally, the root module, the module which you pass as an argument to the Clash compiler must either have: * A function with a 'Synthesize' annotation. * A function called /topEntity/. You apply 'Synthesize' annotations to functions using an @ANN@ pragma: @ {\-\# ANN topEntity (Synthesize {t_name = ..., ... }) \#-\} topEntity x = ... @ For example, given the following specification: @ module Blinker where import "Clash.Signal" import "Clash.Prelude" import "Clash.Intel.ClockGen" 'createDomain' vSystem{vName=\"DomInput\", vPeriod=20000} 'createDomain' vSystem{vName=\"Dom100\", vPeriod=10000} topEntity :: Clock DomInput -> Signal DomInput Bool -> Signal Dom100 Bit -> Signal Dom100 (BitVector 8) topEntity clk rst = 'exposeClockResetEnable' ('mealy' blinkerT (1,False,0) . Clash.Prelude.isRising 1) pllOut rstSync 'enableGen' where (pllOut,pllStable) = 'Clash.Intel.ClockGen.altpll' \@Dom100 (SSymbol \@\"altpll100\") clk ('Clash.Signal.unsafeFromLowPolarity' rst) rstSync = 'Clash.Signal.resetSynchronizer' pllOut ('Clash.Signal.unsafeFromLowPolarity' pllStable) blinkerT (leds,mode,cntr) key1R = ((leds',mode',cntr'),leds) where -- clock frequency = 100e6 (100 MHz) -- led update rate = 333e-3 (every 333ms) cnt_max = 'maxBound' :: ('Index' 33300000) -- 100e6 * 333e-3 cntr' | cntr == cnt_max = 0 | otherwise = cntr + 1 mode' | key1R = not mode | otherwise = mode leds' | cntr == 0 = if mode then complement leds else rotateL leds 1 | otherwise = leds @ The Clash compiler will normally generate the following @topentity.vhdl@ file: @ -- Automatically generated VHDL-93 library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.NUMERIC_STD.ALL; use IEEE.MATH_REAL.ALL; use std.textio.all; use work.all; use work.Blinker_topEntity_types.all; entity topEntity is port(-- clock clk : in Blinker_topEntity_types.clk_DomInput; rst : in boolean; x : in std_logic; result : out std_logic_vector(7 downto 0)); end; architecture structural of topEntity is ... end; @ However, if we add the following 'Synthesize' annotation in the file: @ {\-\# ANN topEntity ('Synthesize' { t_name = "blinker" , t_inputs = [PortName \"CLOCK_50\", PortName \"KEY0\", PortName \"KEY1\"] , t_output = PortName \"LED\" }) \#-\} @ The Clash compiler will generate the following @blinker.vhdl@ file instead: @ -- Automatically generated VHDL-93 library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.NUMERIC_STD.ALL; use IEEE.MATH_REAL.ALL; use std.textio.all; use work.all; use work.blinker_types.all; entity blinker is port(-- clock CLOCK_50 : in blinker_types.clk_dominput; KEY0 : in boolean; KEY1 : in std_logic; LED : out std_logic_vector(7 downto 0)); end; architecture structural of blinker is ... end; @ Where we now have: * A top-level component that is called @blinker@. * Inputs and outputs that have a /user/-chosen name: @CLOCK_50@, @KEY0@, @KEY1@, @LED@, etc. See the documentation of 'Synthesize' for the meaning of all its fields. -} {- $primitives #primitives# There are times when you already have an existing piece of IP, or there are times where you need the VHDL to have a specific shape so that the VHDL synthesis tool can infer a specific component. In these specific cases you can resort to defining your own VHDL primitives. Actually, most of the primitives in Clash are specified in the same way as you will read about in this section. There are perhaps 10 (at most) functions which are truly hard-coded into the Clash compiler. You can take a look at the files in <https://github.com/clash-lang/clash-compiler/tree/master/clash-lib/prims/vhdl> (or <https://github.com/clash-lang/clash-compiler/tree/master/clash-lib/prims/verilog> for the Verilog primitives or <https://github.com/clash-lang/clash-compiler/tree/master/clash-lib/prims/systemverilog> for the SystemVerilog primitives) if you want to know which functions are defined as \"regular\" primitives. The compiler looks for primitives in four locations: * The official install location: e.g. * @$CABAL_DIR\/share\/\<GHC_VERSION\>\/clash-lib\-<VERSION\>\/prims\/common@ * @$CABAL_DIR\/share\/\<GHC_VERSION\>\/clash-lib\-<VERSION\>\/prims\/commonverilog@ * @$CABAL_DIR\/share\/\<GHC_VERSION\>\/clash-lib\-<VERSION\>\/prims\/systemverilog@ * @$CABAL_DIR\/share\/\<GHC_VERSION\>\/clash-lib\-<VERSION\>\/prims\/verilog@ * @$CABAL_DIR\/share\/\<GHC_VERSION\>\/clash-lib\-<VERSION\>\/prims\/vhdl@ * Directories indicated by a 'Clash.Annotations.Primitive.Primitive' annotation * The current directory (the location given by @pwd@) * The include directories specified on the command-line: @-i\<DIR\>@ Where redefined primitives in the current directory or include directories will overwrite those in the official install location. For now, files containing primitive definitions must have a @.primitives.yaml@ file-extension. Clash differentiates between two types of primitives, /expression/ primitives and /declaration/ primitives, corresponding to whether the primitive is a VHDL /expression/ or a VHDL /declaration/. We will first explore /expression/ primitives, using 'Signed' multiplication (@*@) as an example. The "Clash.Sized.Internal.Signed" module specifies multiplication as follows: @ (*#) :: 'GHC.TypeLits.KnownNat' n => 'Signed' n -> 'Signed' n -> 'Signed' n (S a) *# (S b) = fromInteger_INLINE (a * b) {\-\# NOINLINE (*#) \#-\} @ For which the VHDL /expression/ primitive is: @ BlackBox: name: \'Clash.Sized.Internal.Signed.*#\' kind: \'Expression\' type: \'(*#) :: KnownNat n => Signed n -> Signed n -> Signed n\' template: \'resize(~ARG[1] * ~ARG[2], ~LIT[0])\' @ The @name@ of the primitive is the /fully qualified/ name of the function you are creating the primitive for. Because we are creating an /expression/ primitive the kind must be set to @Expression@. As the name suggest, it is a VHDL /template/, meaning that the compiler must fill in the holes heralded by the tilde (~). Here: * @~ARG[1]@ denotes the second argument given to the @(*#)@ function, which corresponds to the LHS of the (@*@) operator. * @~ARG[2]@ denotes the third argument given to the @(*#)@ function, which corresponds to the RHS of the (@*@) operator. * @~LIT[0]@ denotes the first argument given to the @(*#)@ function, with the extra condition that it must be a @LIT@eral. If for some reason this first argument does not turn out to be a literal then the compiler will raise an error. This first arguments corresponds to the \"@'KnownNat' n@\" class constraint. An extensive list with all of the template holes will be given the end of this section. What we immediately notice is that class constraints are counted as normal arguments in the primitive definition. This is because these class constraints are actually represented by ordinary record types, with fields corresponding to the methods of the type class. In the above case, 'KnownNat' is actually just like a @newtype@ wrapper for 'Integer'. The second kind of primitive that we will explore is the /declaration/ primitive. We will use @blockRam#@ as an example, for which the Haskell/Clash code is: @ {\-\# LANGUAGE BangPatterns \#\-\} module BlockRam where import Clash.Explicit.Prelude import Clash.Annotations.Primitive (hasBlackBox) import Clash.Signal.Internal (Clock, Signal (..), (.&&.)) import Clash.Sized.Vector (Vec, toList) import Clash.XException (defaultSeqX) import qualified Data.Vector as V import GHC.Stack (HasCallStack, withFrozenCallStack) blockRam# :: ( KnownDomain dom , HasCallStack , NFDataX a ) => 'Clock' dom -- ^ 'Clock' to synchronize to -> 'Enable' dom -- ^ Global enable -> 'Vec' n a -- ^ Initial content of the BRAM, also -- determines the size, @n@, of the BRAM. -- -- __NB__: __MUST__ be a constant. -> 'Signal' dom Int -- ^ Read address @r@ -> 'Signal' dom Bool -- ^ Write enable -> 'Signal' dom Int -- ^ Write address @w@ -> 'Signal' dom a -- ^ Value to write (at address @w@) -> 'Signal' dom a -- ^ Value of the @blockRAM@ at address @r@ from -- the previous clock cycle blockRam# (Clock _) gen content rd wen = go (V.fromList ('toList' content)) (withFrozenCallStack ('deepErrorX' "blockRam: intial value undefined")) (fromEnable gen) rd (fromEnable gen '.&&.' wen) where go !ram o ret\@(~(re :- res)) rt\@(~(r :- rs)) et\@(~(e :- en)) wt\@(~(w :- wr)) dt\@(~(d :- din)) = let ram' = d ``defaultSeqX`` upd ram e (fromEnum w) d o' = if re then ram V.! r else o in o ``seqX`` o :- (ret ``seq`` rt ``seq`` et ``seq`` wt ``seq`` dt ``seq`` go ram' o' res rs en wr din) upd ram we waddr d = case maybeIsX we of Nothing -> case maybeIsX waddr of Nothing -> V.map (const (seq waddr d)) ram Just wa -> ram V.// [(wa,d)] Just True -> case maybeIsX waddr of Nothing -> V.map (const (seq waddr d)) ram Just wa -> ram V.// [(wa,d)] _ -> ram {\-\# NOINLINE blockRam# \#\-\} {\-\# ANN blockRam# hasBlackBox \#\-\} @ And for which the /declaration/ primitive is: @ BlackBox: name: Clash.Explicit.BlockRam.blockRam# kind: Declaration type: |- blockRam# :: ( KnownDomain dom ARG[0] , HasCallStack -- ARG[1] , NFDataX a ) -- ARG[2] => Clock dom -- clk, ARG[3] -> Enable dom -- en, ARG[4] -> Vec n a -- init, ARG[5] -> Signal dom Int -- rd, ARG[6] -> Signal dom Bool -- wren, ARG[7] -> Signal dom Int -- wr, ARG[8] -> Signal dom a -- din, ARG[9] -> Signal dom a template: |- -- blockRam begin ~GENSYM[~RESULT_blockRam][1] : block signal ~GENSYM[~RESULT_RAM][2] : ~TYP[5] := ~CONST[5]; signal ~GENSYM[rd][4] : integer range 0 to ~LENGTH[~TYP[5]] - 1; signal ~GENSYM[wr][5] : integer range 0 to ~LENGTH[~TYP[5]] - 1; begin ~SYM[4] <= to_integer(~ARG[6]) -- pragma translate_off mod ~LENGTH[~TYP[5]] -- pragma translate_on ; ~SYM[5] <= to_integer(~ARG[8]) -- pragma translate_off mod ~LENGTH[~TYP[5]] -- pragma translate_on ; ~IF ~VIVADO ~THEN ~SYM[6] : process(~ARG[3]) begin if ~IF~ACTIVEEDGE[Rising][0]~THENrising_edge~ELSEfalling_edge~FI(~ARG[3]) then if ~ARG[7] ~IF ~ISACTIVEENABLE[4] ~THEN and ~ARG[4] ~ELSE ~FI then ~SYM[2](~SYM[5]) <= ~TOBV[~ARG[9]][~TYP[9]]; end if; ~RESULT <= fromSLV(~SYM[2](~SYM[4])) -- pragma translate_off after 1 ps -- pragma translate_on ; end if; end process; ~ELSE ~SYM[6] : process(~ARG[3]) begin if ~IF~ACTIVEEDGE[Rising][0]~THENrising_edge~ELSEfalling_edge~FI(~ARG[3]) then if ~ARG[7] ~IF ~ISACTIVEENABLE[4] ~THEN and ~ARG[4] ~ELSE ~FI then ~SYM[2](~SYM[5]) <= ~ARG[9]; end if; ~RESULT <= ~SYM[2](~SYM[4]) -- pragma translate_off after 1 ps -- pragma translate_on ; end if; end process; ~FI end block; --end blockRam @ Again, the @name@ of the primitive is the fully qualified name of the function you are creating the primitive for. Because we are creating a /declaration/ primitive the /kind/ must be set to @Declaration@. Instead of discussing what the individual template holes mean in the above context, we will instead just give a general listing of the available template holes: * @~RESULT@: Signal to which the result of a primitive must be assigned to. NB: Only used in a /declaration/ primitive. * @~ARG[N]@: @(N+1)@'th argument to the function. * @~CONST[N]@: @(N+1)@'th argument to the function. Like @~ARG@, but Clash will try to reduce this to a literal, even if it would otherwise consider it too expensive. And if Clash fails to reduce this argument to a literal it will produce an error. * @~LIT[N]@: @(N+1)@'th argument to the function. Like @~CONST~ but values are rendered as a bare literals, without any size or type annotations. This only works for numeric types, and not for BitVector. * @~TYP[N]@: VHDL type of the @(N+1)@'th argument. * @~TYPO@: VHDL type of the result. * @~TYPM[N]@: VHDL type/name/ of the @(N+1)@'th argument; used in /type/ /qualification/. * @~TYPMO@: VHDL type/name/ of the result; used in /type qualification/. * @~ERROR[N]@: Error value for the VHDL type of the @(N+1)@'th argument. * @~ERRORO@: Error value for the VHDL type of the result. * @~GENSYM[\<NAME\>][N]@: Create a unique name, trying to stay as close to the given @\<NAME\>@ as possible. This unique symbol can be referred to in other places using @~SYM[N]@. * @~SYM[N]@: a reference to the unique symbol created by @~GENSYM[\<NAME\>][N]@. * @~SIGD[\<HOLE\>][N]@: Create a signal declaration, using @\<HOLE\>@ as the name of the signal, and the type of the @(N+1)@'th argument. * @~SIGDO[\<HOLE\>]@: Create a signal declaration, using @\<HOLE\>@ as the name of the signal, and the type of the result. * @~TYPEL[\<HOLE\>]@: The element type of the vector type represented by @\<HOLE\>@. The content of @\<HOLE\>@ must either be: @~TYP[N]@, @~TYPO@, or @~TYPEL[\<HOLE\>]@. * @~COMPNAME@: The name of the component in which the primitive is instantiated. * @~LENGTH[\<HOLE\>]@: The vector length of the type represented by @\<HOLE\>@. * @~DEPTH[\<HOLE\>]@: The tree depth of the type represented by @\<HOLE\>@. The content of @\<HOLE\>@ must either be: @~TYP[N]@, @~TYPO@, or @~TYPEL[\<HOLE\>]@. * @~SIZE[\<HOLE\>]@: The number of bits needed to encode the type represented by @\<HOLE\>@. The content of @\<HOLE\>@ must either be: @~TYP[N]@, @~TYPO@, or @~TYPEL[\<HOLE\>]@. * @~IF \<CONDITION\> ~THEN \<THEN\> ~ELSE \<ELSE\> ~FI@: renders the @\<ELSE\>@ part when @\<CONDITION\>@ evaluates to /0/, and renders the @\<THEN\>@ in all other cases. Valid @\<CONDITION\>@s are @~LENGTH[\<HOLE\>]@, @~SIZE[\<HOLE\>]@, @~CMPLE[\<HOLE1\>][\<HOLE2\>]@, @~DEPTH[\<HOLE\>]@, @~VIVADO@, @~IW64@, @~ISLIT[N]@, @~ISVAR[N]@, @~ISACTIVEENABLE[N]@, @~ISSYNC[N]@, and @~AND[\<HOLE1\>,\<HOLE2\>,..]@. * @~VIVADO@: /1/ when Clash compiler is invoked with the @-fclash-xilinx@ or @-fclash-vivado@ flag. To be used with in an @~IF .. ~THEN .. ~ELSE .. ~FI@ statement. * @~CMPLE[\<HOLE1\>][\<HOLE2\>]@: /1/ when @\<HOLE1\> \<= \<HOLE2\>@, otherwise /0/ * @~IW64@: /1/ when Int/Word/Integer types are represented with 64 bits in HDL. /0/ when they're represented by 32 bits. * @~TOBV[\<HOLE\>][\<TYPE\>]@: create conversion code that so that the expression in @\<HOLE\>@ is converted to a bit vector (@std_logic_vector@). The @\<TYPE\>@ hole indicates the type of the expression and must be either @~TYP[N]@, @~TYPO@, or @~TYPEL[\<HOLE\>]@. * @~FROMBV[\<HOLE\>][\<TYPE\>]@: create conversion code that so that the expression in @\<HOLE\>@, which has a bit vector (@std_logic_vector@) type, is converted to type indicated by @\<TYPE\>@. The @\<TYPE\>@ hole must be either @~TYP[N]@, @~TYPO@, or @~TYPEL[\<HOLE\>]@. * @~INCLUDENAME[N]@: the generated name of the @N@'th included component. * @~FILE[\<HOLE\>]@: The argument mentioned in @\<HOLE\>@ is a file which must be copied to the location of the generated HDL. * @~GENERATE@: Verilog: create a /generate/ statement, except when already in a /generate/ context. * @~ENDGENERATE@: Verilog: create an /endgenerate/ statement, except when already in a /generate/ context. * @~ISLIT[N]@: Is the @(N+1)@'th argument to the function a literal. * @~ISVAR[N]@: Is the @(N+1)@'th argument to the function explicitly not a literal. * @~ISSCALAR[N]@: Is the @(N+1)@'th argument to the function a scalar. Note that this means different things for different HDLs. In (System)Verilog only @Bit@ and @Bool@ are considered scalar. In VHDL, in addition to those two, enumeration types and integers are considered scalar. * @~TAG[N]@: Name of given domain. Errors when called on an argument which is not a 'KnownDomain', 'Reset', or 'Clock'. * @~PERIOD[N]@: Clock period of given domain. Errors when called on an argument which is not a 'KnownDomain' or 'KnownConf'. * @~ISACTIVEENABLE[N]@: Is the @(N+1)@'th argument a an Enable line NOT set to a constant True. Can be used instead of deprecated (and removed) template tag * @~ISSYNC[N]@: Does synthesis domain at the @(N+1)@'th argument have synchronous resets. Errors when called on an argument which is not a 'KnownDomain' or 'KnownConf'. * @~ISINITDEFINED[N]@: Does synthesis domain at the @(N+1)@'th argument have defined initial values. Errors when called on an argument which is not a 'KnownDomain' or 'KnownConf'. * @~ACTIVEEDGE[edge][N]@: Does synthesis domain at the @(N+1)@'th argument respond to /edge/. /edge/ must be one of 'Falling' or 'Rising'. Errors when called on an argument which is not a 'KnownDomain' or 'KnownConf'. * @~AND[\<HOLE1\>,\<HOLE2\>,..]@: Logically /and/ the conditions in the @\<HOLE\>@'s * @~VAR[\<NAME\>][N]@: Like @~ARG[N]@ but binds the argument to a variable named NAME. The @\<NAME\>@ can be left blank, then clash will come up with a (unique) name. * @~VARS[N]@: VHDL: Return the variables at the @(N+1)@'th argument. * @~NAME[N]@: Render the @(N+1)@'th string literal argument as an identifier instead of a string literal. Fails when the @(N+1)@'th argument is not a string literal. * @~DEVNULL[\<HOLE\>]@: Render all dependencies of @\<HOLE\>@, but disregard direct output. * @~REPEAT[\<HOLE\>][N]@: Repeat literal value of @\<HOLE\>@ a total of @N@ times. * @~TEMPLATE[\<HOLE1\>][\<HOLE2\>]@: Render a file @\<HOLE1\>@ with contents @\<HOLE2\>@. Some final remarks to end this section: VHDL primitives are there to instruct the Clash compiler to use the given VHDL template, instead of trying to do normal synthesis. As a consequence you can use constructs inside the Haskell definitions that are normally not synthesizable by the Clash compiler. However, VHDL primitives do not give us /co-simulation/: where you would be able to simulate VHDL and Haskell in a /single/ environment. If you still want to simulate your design in Haskell, you will have to describe, in a cycle- and bit-accurate way, the behavior of that (potentially complex) IP you are trying to include in your design. Perhaps in the future, someone will figure out how to connect the two simulation worlds, using e.g. VHDL's foreign function interface VHPI. -} {- $vprimitives For those who are interested, the equivalent Verilog primitives are: @ BlackBox: name: Clash.Sized.Internal.Signed.*# kind: Expression type: \'(*#) :: KnownNat n => Signed n -> Signed n -> Signed n\' template: ~ARG[1] * ~ARG[2] @ and @ BlackBox: name: Clash.Explicit.BlockRam.blockRam# kind: Declaration outputReg: true type: |- blockRam# :: ( KnownDomain dom ARG[0] , HasCallStack -- ARG[1] , NFDataX a ) -- ARG[2] => Clock dom -- clk, ARG[3] => Enable dom -- en, ARG[4] -> Vec n a -- init, ARG[5] -> Signal dom Int -- rd, ARG[6] -> Signal dom Bool -- wren, ARG[7] -> Signal dom Int -- wr, ARG[8] -> Signal dom a -- din, ARG[9] -> Signal dom a template: |- // blockRam begin reg ~TYPO ~GENSYM[~RESULT_RAM][1] [0:~LENGTH[~TYP[5]]-1]; reg ~TYP[5] ~GENSYM[ram_init][3]; integer ~GENSYM[i][4]; initial begin ~SYM[3] = ~CONST[5]; for (~SYM[4]=0; ~SYM[4] < ~LENGTH[~TYP[5]]; ~SYM[4] = ~SYM[4] + 1) begin ~SYM[1][~LENGTH[~TYP[5]]-1-~SYM[4]] = ~SYM[3][~SYM[4]*~SIZE[~TYPO]+:~SIZE[~TYPO]]; end end ~IF ~ISACTIVEENABLE[4] ~THEN always @(~IF~ACTIVEEDGE[Rising][0]~THENposedge~ELSEnegedge~FI ~ARG[3]) begin : ~GENSYM[~RESULT_blockRam][5]~IF ~VIVADO ~THEN if (~ARG[4]) begin if (~ARG[7]) begin ~SYM[1][~ARG[8]] <= ~ARG[9]; end ~RESULT <= ~SYM[1][~ARG[6]]; end~ELSE if (~ARG[7] & ~ARG[4]) begin ~SYM[1][~ARG[8]] <= ~ARG[9]; end if (~ARG[4]) begin ~RESULT <= ~SYM[1][~ARG[6]]; end~FI end~ELSE always @(~IF~ACTIVEEDGE[Rising][0]~THENposedge~ELSEnegedge~FI ~ARG[3]) begin : ~SYM[5] if (~ARG[7]) begin ~SYM[1][~ARG[8]] <= ~ARG[9]; end ~RESULT <= ~SYM[1][~ARG[6]]; end~FI // blockRam end @ -} {- $svprimitives And the equivalent SystemVerilog primitives are: @ BlackBox: name: Clash.Sized.Internal.Signed.*# kind: Expression type: \'(*#) :: KnownNat n => Signed n -> Signed n -> Signed n\' template: ~ARG[1] * ~ARG[2] @ and @ BlackBox: name: Clash.Explicit.BlockRam.blockRam# kind: Declaration type: |- blockRam# :: ( KnownDomain dom ARG[0] , HasCallStack -- ARG[1] , NFDataX a ) -- ARG[2] => Clock dom -- clk, ARG[3] -> Enable dom -- en, ARG[4] -> Vec n a -- init, ARG[5] -> Signal dom Int -- rd, ARG[6] -> Signal dom Bool -- wren, ARG[7] -> Signal dom Int -- wr, ARG[8] -> Signal dom a -- din, ARG[9] -> Signal dom a template: |- // blockRam begin ~SIGD[~GENSYM[RAM][1]][5]; logic [~SIZE[~TYP[9]]-1:0] ~GENSYM[~RESULT_q][2]; initial begin ~SYM[1] = ~CONST[5]; end~IF ~ISACTIVEENABLE[4] ~THEN always @(~IF~ACTIVEEDGE[Rising][0]~THENposedge~ELSEnegedge~FI ~ARG[3]) begin : ~GENSYM[~COMPNAME_blockRam][3]~IF ~VIVADO ~THEN if (~ARG[4]) begin if (~ARG[7]) begin ~SYM[1][~ARG[8]] <= ~TOBV[~ARG[9]][~TYP[9]]; end ~SYM[2] <= ~SYM[1][~ARG[6]]; end~ELSE if (~ARG[7] & ~ARG[4]) begin ~SYM[1][~ARG[8]] <= ~TOBV[~ARG[9]][~TYP[9]]; end if (~ARG[4]) begin ~SYM[2] <= ~SYM[1][~ARG[6]]; end~FI end~ELSE always @(~IF~ACTIVEEDGE[Rising][0]~THENposedge~ELSEnegedge~FI ~ARG[3]) begin : ~SYM[3] if (~ARG[7]) begin ~SYM[1][~ARG[8]] <= ~TOBV[~ARG[9]][~TYP[9]]; end ~SYM[2] <= ~SYM[1][~ARG[6]]; end~FI assign ~RESULT = ~FROMBV[~SYM[2]][~TYP[9]]; // blockRam end @ -} {- $multiclock #multiclock# Clash supports designs multiple /clock/ (and /reset/) domains, though perhaps in a slightly limited form. What is possible is: * Create clock primitives, such as PLLs, which have an accompanying HDL primitive (described <#primitives later on> in this tutorial). * Explicitly assign clocks to memory primitives. * Synchronize between differently-clocked parts of your design in a type-safe way. What is /not/ possible is: * Directly generate a clock signal in module A, and assign this clock signal to a memory primitive in module B. For example, the following is not possible: @ pow2Clocks :: ( 'KnownConfiguration' domIn (''DomainConfiguration' domIn pIn eIn rIn iIn polIn) , 'KnownConfiguration' dom2 (''DomainConfiguration' dom2 (2*pIn) e2 r2 i2 p2) , 'KnownConfiguration' dom4 (''DomainConfiguration' dom4 (4*pIn) e4 r4 i4 p4) , 'KnownConfiguration' dom8 (''DomainConfiguration' dom8 (8*pIn) e8 r8 i8 p8) , 'KnownConfiguration' dom16 (''DomainConfiguration' dom16 (16*pIn) e16 r16 i16 p16) => 'Clock' domIn -> 'Reset' domIn -> ( 'Clock' dom16 , 'Clock' dom8 , 'Clock' dom4 , 'Clock' dom2 ) pow2Clocks clk rst = (cnt!3, cnt!2, cnt!1, cnt!0) where cnt = 'Clash.Explicit.Signal.register' clk rst 0 (cnt + 1) @ As it is not possible to convert the individual bits to a 'Clock'. However! What is possible is to do the following: @ pow2Clocks' :: ( 'KnownConfiguration' domIn (''DomainConfiguration' domIn pIn eIn rIn iIn polIn) , 'KnownConfiguration' dom2 (''DomainConfiguration' dom2 (2*pIn) e2 r2 i2 p2) , 'KnownConfiguration' dom4 (''DomainConfiguration' dom4 (4*pIn) e4 r4 i4 p4) , 'KnownConfiguration' dom8 (''DomainConfiguration' dom8 (8*pIn) e8 r8 i8 p8) , 'KnownConfiguration' dom16 (''DomainConfiguration' dom16 (16*pIn) e16 r16 i16 p16) => 'Clock' domIn -> 'Reset' domIn -> ( 'Clock' dom16 , 'Clock' dom8 , 'Clock' dom4 , 'Clock' dom2 ) pow2Clocks' clk rst = ('clockGen', 'clockGen', 'clockGen', 'clockGen') {\-\# NOINLINE pow2Clocks' \#-\} @ And then create a HDL primitive, as described in later on in this <#primitives tutorial>, to implement the desired behavior in HDL. What this means is that when Clash converts your design to VHDL/(System)Verilog, you end up with a top-level module/entity with multiple clock and reset ports for the different clock domains. If you're targeting an FPGA, you can use e.g. a <https://www.altera.com/literature/ug/ug_altpll.pdf PLL> or <http://www.xilinx.com/support/documentation/user_guides/ug472_7Series_Clocking.pdf MMCM> to provide the clock signals. == Building a FIFO synchronizer This part of the tutorial assumes you know what <https://en.wikipedia.org/wiki/Metastability_in_electronics metastability> is, and how it can never truly be avoided in any asynchronous circuit. Also it assumes that you are familiar with the design of synchronizer circuits, and why a dual flip-flop synchronizer only works for bit-synchronization and not word-synchronization. The explicitly clocked versions of all synchronous functions and primitives can be found in "Clash.Explicit.Prelude", which also re-exports the functions in "Clash.Signal.Explicit". We will use those functions to create a FIFO where the read and write port are synchronized to different clocks. Below you can find the code to build the FIFO synchronizer based on the design described in: <http://www.sunburst-design.com/papers/CummingsSNUG2002SJ_FIFO1.pdf> We start with enable a few options that will make writing the type-signatures for our components a bit easier. Instead of importing the standard "Clash.Prelude" module, we will import the "Clash.Explicit.Prelude" module where all our clocks and resets must be explicitly routed (other imports will be used later): @ module MultiClockFifo where import "Clash.Explicit.Prelude" import "Clash.Prelude" (mux) import Data.Maybe (isJust) import Data.Constraint (Dict (..), (:-)( Sub )) import Data.Constraint.Nat (leTrans) @ Then we'll start with the /heart/ of the FIFO synchronizer, an asynchronous RAM in the form of 'asyncRam'. It's called an asynchronous RAM because the read port is not synchronized to any clock (though the write port is). Note that in Clash we don't really have asynchronous logic, there is only combinational and synchronous logic. As a consequence, we see in the type signature of 'Clash.Explicit.Prelude.asyncRam': @ __asyncRam__ :: ( 'Enum' addr , 'HasCallStack' , 'KnownDomain' wdom , 'KnownDomain' rdom ) => 'Clock' wdom -- ^ 'Clock' to which to synchronize the write port of the RAM -> 'Clock' rdom -- ^ 'Clock' to which the read address signal, @r@, is synchronized to -> 'Enable' wdom -- ^ Global enable -> 'SNat' n -- ^ Size @n@ of the RAM -> 'Signal' rdom addr -- ^ Read address @r@ -> 'Signal' wdom (Maybe (addr, a)) -- ^ (write address @w@, value to write) -> 'Signal' rdom a -- ^ Value of the @RAM@ at address @r@ @ that the signal containing the read address __r__ is synchronized to a different clock. That is, there is __no__ such thing as an @AsyncSignal@ in Clash. We continue by instantiating the 'Clash.Explicit.Prelude.asyncRam': @ fifoMem wclk rclk en addrSize\@SNat full raddr writeM = 'Clash.Explicit.Prelude.asyncRam' wclk rclk en ('pow2SNat' addrSize) raddr ('mux' full (pure Nothing) writeM) @ We see that we give it @2^addrSize@ elements, where @addrSize@ is the bit-size of the address. Also, we only write new values to the RAM when a new write is requested, indicated by @wdataM@ having a 'Data.Maybe.Just' value, and the buffer is not full, indicated by @wfull@. The next part of the design calculates the read and write address for the asynchronous RAM, and creates the flags indicating whether the FIFO is full or empty. The address and flag generator is given in 'mealy' machine style: @ ptrCompareT :: SNat addrSize -> (BitVector (addrSize + 1) -> BitVector (addrSize + 1) -> Bool) -> ( BitVector (addrSize + 1) , BitVector (addrSize + 1) , Bool ) -> ( BitVector (addrSize + 1) , Bool ) -> ( ( BitVector (addrSize + 1) , BitVector (addrSize + 1) , Bool ) , ( Bool , BitVector addrSize , BitVector (addrSize + 1) ) ) ptrCompareT addrSize\@SNat flagGen (bin, ptr, flag) (s_ptr, inc) = ( (bin', ptr', flag') , (flag, addr, ptr) ) where -- GRAYSTYLE2 pointer bin' = bin + 'boolToBV' (inc && not flag) ptr' = (bin' \`shiftR\` 1) \`xor\` bin' addr = 'truncateB' bin flag' = flagGen ptr' s_ptr @ It is parametrized in both address size, @addrSize@, and status flag generator, @flagGen@. It has two inputs, @s_ptr@, the synchronized pointer from the other clock domain, and @inc@, which indicates we want to perform a write or read of the FIFO. It creates three outputs: @flag@, the full or empty flag, @addr@, the read or write address into the RAM, and @ptr@, the Gray-encoded version of the read or write address which will be synchronized between the two clock domains. Next follow the initial states of address generators, and the flag generators for the empty and full flags: @ -- FIFO empty: when next pntr == synchronized wptr or on reset isEmpty = (==) rptrEmptyInit = (0, 0, True) -- FIFO full: when next pntr == synchronized {~wptr[addrSize:addrSize-1],wptr[addrSize-2:0]} isFull :: forall addrSize . (2 <= addrSize) => 'SNat' addrSize -> 'BitVector' (addrSize + 1) -> 'BitVector' (addrSize + 1) -> Bool isFull addrSize\@SNat ptr s_ptr = case leTrans \@1 \@2 \@addrSize of Sub Dict -> let a1 = 'SNat' \@(addrSize - 1) a2 = 'SNat' \@(addrSize - 2) in ptr == ('complement' ('slice' addrSize a1 s_ptr) '++#' 'slice' a2 d0 s_ptr) wptrFullInit = (0, 0, False) @ We create a dual flip-flop synchronizer to be used to synchronize the Gray-encoded pointers between the two clock domains: @ ptrSync clk1 clk2 rst2 en2 = 'Clash.Explicit.Signal.register' clk2 rst2 en2 0 . 'Clash.Explicit.Signal.register' clk2 rst2 en2 0 . 'Clash.Explicit.Signal.unsafeSynchronizer' clk1 clk2 @ It uses the 'Clash.Explicit.Signal.unsafeSynchronizer' primitive, which is needed to go from one clock domain to the other. All synchronizers are specified in terms of 'Clash.Explicit.Signal.unsafeSynchronizer' (see for example the <src/Clash-Prelude-RAM.html#line-103 source of asyncRam>). The 'Clash.Explicit.Signal.unsafeSynchronizer' primitive is turned into a (bundle of) wire(s) by the Clash compiler, so developers must ensure that it is only used as part of a proper synchronizer. Finally we combine all the components in: @ asyncFIFOSynchronizer :: ( 'KnownDomain' wdom , 'KnownDomain' rdom , 2 <= addrSize ) => SNat addrSize -- ^ Size of the internally used addresses, the FIFO contains @2^addrSize@ -- elements. -> 'Clock' wdom -- ^ 'Clock' to which the write port is synchronized -> 'Clock' rdom -- ^ 'Clock' to which the read port is synchronized -> 'Reset' wdom -> 'Reset' rdom -> 'Enable' wdom -> 'Enable' rdom -> 'Signal' rdom Bool -- ^ Read request -> 'Signal' wdom (Maybe a) -- ^ Element to insert -> ('Signal' rdom a, 'Signal' rdom Bool, 'Signal' wdom Bool) -- ^ (Oldest element in the FIFO, @empty@ flag, @full@ flag) asyncFIFOSynchronizer addrSize\@SNat wclk rclk wrst rrst wen ren rinc wdataM = (rdata, rempty, wfull) where s_rptr = ptrSync rclk wclk wrst wen rptr s_wptr = ptrSync wclk rclk rrst ren wptr rdata = fifoMem wclk rclk wen addrSize wfull raddr (liftA2 (,) \<$\> (pure \<$\> waddr) \<*\> wdataM) (rempty, raddr, rptr) = 'mealyB' rclk rrst ren (ptrCompareT addrSize isEmpty) (0, 0, True) (s_wptr, rinc) (wfull, waddr, wptr) = 'mealyB' wclk wrst wen (ptrCompareT addrSize (isFull addrSize)) (0, 0, False) (s_rptr, isJust \<$\> wdataM) @ where we first specify the synchronization of the read and the write pointers, instantiate the asynchronous RAM, and instantiate the read address \/ pointer \/ flag generator and write address \/ pointer \/ flag generator. Ultimately, the whole file containing our FIFO design will look like this: @ module MultiClockFifo where import "Clash.Explicit.Prelude" import "Clash.Prelude" (mux) import Data.Maybe (isJust) import Data.Constraint (Dict (..), (:-)( Sub )) import Data.Constraint.Nat (leTrans) fifoMem wclk rclk en addrSize\@SNat full raddr writeM = 'Clash.Explicit.Prelude.asyncRam' wclk rclk en ('pow2SNat' addrSize) raddr ('mux' full (pure Nothing) writeM) ptrCompareT :: SNat addrSize -> (BitVector (addrSize + 1) -> BitVector (addrSize + 1) -> Bool) -> ( BitVector (addrSize + 1) , BitVector (addrSize + 1) , Bool ) -> ( BitVector (addrSize + 1) , Bool ) -> ( ( BitVector (addrSize + 1) , BitVector (addrSize + 1) , Bool ) , ( Bool , BitVector addrSize , BitVector (addrSize + 1) ) ) ptrCompareT addrSize\@SNat flagGen (bin, ptr, flag) (s_ptr, inc) = ( (bin', ptr', flag') , (flag, addr, ptr) ) where -- GRAYSTYLE2 pointer bin' = bin + 'boolToBV' (inc && not flag) ptr' = (bin' \`shiftR\` 1) \`xor\` bin' addr = 'truncateB' bin flag' = flagGen ptr' s_ptr -- FIFO empty: when next pntr == synchronized wptr or on reset isEmpty = (==) rptrEmptyInit = (0, 0, True) -- FIFO full: when next pntr == synchronized {~wptr[addrSize:addrSize-1],wptr[addrSize-2:0]} isFull :: forall addrSize . (2 <= addrSize) => 'SNat' addrSize -> 'BitVector' (addrSize + 1) -> 'BitVector' (addrSize + 1) -> Bool isFull addrSize\@SNat ptr s_ptr = case leTrans \@1 \@2 \@addrSize of Sub Dict -> let a1 = 'SNat' \@(addrSize - 1) a2 = 'SNat' \@(addrSize - 2) in ptr == ('complement' ('slice' addrSize a1 s_ptr) '++#' 'slice' a2 d0 s_ptr) wptrFullInit = (0, 0, False) -- Dual flip-flop synchronizer ptrSync clk1 clk2 rst2 en2 = 'Clash.Explicit.Signal.register' clk2 rst2 en2 0 . 'Clash.Explicit.Signal.register' clk2 rst2 en2 0 . 'Clash.Explicit.Signal.unsafeSynchronizer' clk1 clk2 -- Async FIFO synchronizer asyncFIFOSynchronizer :: ( 'KnownDomain' wdom , 'KnownDomain' rdom , 2 <= addrSize ) => SNat addrSize -- ^ Size of the internally used addresses, the FIFO contains @2^addrSize@ -- elements. -> 'Clock' wdom -- ^ Clock to which the write port is synchronized -> 'Clock' rdom -- ^ Clock to which the read port is synchronized -> 'Reset' wdom -> 'Reset' rdom -> 'Enable' wdom -> 'Enable' rdom -> 'Signal' rdom Bool -- ^ Read request -> 'Signal' wdom (Maybe a) -- ^ Element to insert -> ('Signal' rdom a, 'Signal' rdom Bool, 'Signal' wdom Bool) -- ^ (Oldest element in the FIFO, @empty@ flag, @full@ flag) asyncFIFOSynchronizer addrSize\@SNat wclk rclk wrst rrst wen ren rinc wdataM = (rdata, rempty, wfull) where s_rptr = ptrSync rclk wclk wrst wen rptr s_wptr = ptrSync wclk rclk rrst ren wptr rdata = fifoMem wclk rclk wen addrSize wfull raddr (liftA2 (,) \<$\> (pure \<$\> waddr) \<*\> wdataM) (rempty, raddr, rptr) = 'mealyB' rclk rrst ren (ptrCompareT addrSize isEmpty) (0, 0, True) (s_wptr, rinc) (wfull, waddr, wptr) = 'mealyB' wclk wrst wen (ptrCompareT addrSize (isFull addrSize)) (0, 0, False) (s_rptr, isJust \<$\> wdataM) @ == Instantiating a FIFO synchronizer Having finished our FIFO synchronizer it's time to instantiate with concrete clock domains. Let us assume we have part of our system connected to an ADC which runs at 20 MHz, and we have created an FFT component running at only 9 MHz. We want to connect part of our design connected to the ADC, and running at 20 MHz, to part of our design connected to the FFT running at 9 MHz. We can calculate the clock periods using 'hzToPeriod': >>> hzToPeriod 20e6 50000 >>> hzToPeriod 9e6 111111 We can then create the clock and reset domains: @ 'createDomain' vSystem{vName=\"ADC\", vPeriod=hzToPeriod 20e6} 'createDomain' vSystem{vName=\"FFT\", vPeriod=hzToPeriod 9e6} @ and subsequently a 256-space FIFO synchronizer that safely bridges the ADC clock domain and to the FFT clock domain: @ adcToFFT :: 'Clock' \"ADC\" -> 'Clock' \"FFT\" -> 'Reset' \"ADC\" -> 'Reset' \"FFT\" -> 'Enable' \"ADC\" -> 'Enable' \"FFT\" -> 'Signal' \"FFT\" Bool -> 'Signal' \"ADC\" (Maybe (SFixed 8 8)) -> ( 'Signal' \"FFT\" (SFixed 8 8) , 'Signal' \"FFT\" Bool , 'Signal' \"ADC\" Bool ) adcToFFT = asyncFIFOSynchronizer d8 @ -} {- $conclusion For now, this is the end of this tutorial. We will be adding updates over time, so check back from time to time. We recommend that you continue with exploring the "Clash.Prelude" module, and get a better understanding of the capabilities of Clash in the process. -} {- $errorsandsolutions A list of often encountered errors and their solutions: * __Type error: Couldn't match expected type @'Signal' dom (a,b)@ with actual type__ __@('Signal' dom a, 'Signal' dom b)@__: Signals of product types and product types of signals are __isomorphic__ due to synchronisity principle, but are not (structurally) equal. Tuples are a product type. Use the 'bundle' function to convert from a product type to the signal type. So if your code which gives the error looks like: @ ... = f a b (c,d) @ add the 'bundle' function like so: @ ... = f a b ('bundle' (c,d)) @ Product types supported by 'bundle' are: * All tuples up to and including 62-tuples (GHC limit) * The 'Vec'tor type * __Type error: Couldn't match expected type @('Signal' dom a, 'Signal' dom b)@ with__ __ actual type @'Signal' dom (a,b)@__: Product types of signals and signals of product types are __isomorphic__ due to synchronicity principle, but are not (structurally) equal. Tuples are a product type. Use the 'unbundle' function to convert from a signal type to the product type. So if your code which gives the error looks like: @ (c,d) = f a b @ add the 'unbundle' function like so: @ (c,d) = 'unbundle' (f a b) @ Product types supported by 'unbundle' are: * All tuples up to and including 62-tuples (GHC limit) * The 'Vec'tor type * __Clash.Netlist(..): Not in normal form: \<REASON\>: \<EXPR\>__: A function could not be transformed into the expected normal form. This usually means one of the following: * The @topEntity@ has higher-order arguments, or a higher-order result. * You are using types which cannot be represented in hardware. The solution for all the above listed reasons is quite simple: remove them. That is, make sure that the @topEntity@ is completely monomorphic and first-order. Also remove any variables and constants/literals that have a non-representable type; see <#limitations Limitations of Clash> to find out which types are not representable. * __Clash.Normalize(..): Clash can only normalize monomorphic functions, but this is polymorphic__: If this happens for a @topEntity@ or something with a @Synthesize@ annotation, add a monomorphic type signature. Non topEntites should be type-specialized by clash automatically, if not please report this as a bug. But adding a monomorphic type signature should still help (when possible). * __Clash.Normalize(..): Expr belonging to bndr: \<FUNCTION\> remains__ __recursive after normalization__: * If you actually wrote a recursive function, rewrite it to a non-recursive one using e.g. one of the higher-order functions in "Clash.Sized.Vector" :-) * You defined a recursively defined value, but left it polymorphic: @ topEntity x y = acc where acc = 'register' 3 (acc + x * y) @ The above function, works for any number-like type. This means that @acc@ is a recursively defined __polymorphic__ value. Adding a monomorphic type annotation makes the error go away: @ topEntity :: 'SystemClockResetEnable' => 'Signal' 'System' ('Signed' 8) -> 'Signal' 'System' ('Signed' 8) -> 'Signal' 'System' ('Signed' 8) topEntity x y = acc where acc = 'register' 3 (acc + x * y) @ * __Clash.Normalize.Transformations(..): InlineNonRep: \<FUNCTION\> already__ __inlined 100 times in:\<FUNCTION\>, \<TYPE\>__: You left the @topEntity@ function polymorphic or higher-order: use @:t topEntity@ to check if the type is indeed polymorphic or higher-order. If it is, add a monomorphic type signature, and / or supply higher-order arguments. * __\<*** Exception: \<\<loop\>\>__ or "blinking cursor" You are using value-recursion, but one of the 'Vec'tor functions that you are using is too /strict/ in one of the recursive arguments. For example: @ -- Bubble sort for 1 iteration sortV xs = 'map' fst sorted ':<' (snd ('last' sorted)) where lefts = 'head' xs :> 'map' snd ('init' sorted) rights = 'tail' xs sorted = 'zipWith' compareSwapL lefts rights -- Compare and swap compareSwapL a b = if a < b then (a,b) else (b,a) @ Will not terminate because 'zipWith' is too strict in its second argument. In this case, adding 'lazyV' on 'zipWith's second argument: @ sortVL xs = 'map' fst sorted ':<' (snd ('last' sorted)) where lefts = 'head' xs :> map snd ('init' sorted) rights = 'tail' xs sorted = 'zipWith' compareSwapL ('lazyV' lefts) rights @ Results in a successful computation: >>> sortVL (4 :> 1 :> 2 :> 3 :> Nil) 1 :> 2 :> 3 :> 4 :> Nil -} {- $limitations #limitations# Here is a list of Haskell features for which the Clash compiler has only /limited/ support (for now): * __Recursively defined functions__ At first hand, it seems rather bad that a compiler for a functional language cannot synthesize recursively defined functions to circuits. However, when viewing your functions as a /structural/ specification of a circuit, this /feature/ of the Clash compiler makes sense. Also, only certain types of recursion are considered non-synthesizable; recursively defined values are for example synthesizable: they are (often) synthesized to feedback loops. Let us distinguish between three variants of recursion: * __Dynamic data-dependent recursion__ As demonstrated in this definition of a function that calculates the n'th Fibbonacci number: @ fibR 0 = 0 fibR 1 = 1 fibR n = fibR (n-1) + fibR (n-2) @ To get the first 10 numbers, we do the following: >>> import qualified Data.List as L >>> L.map fibR [0..9] [0,1,1,2,3,5,8,13,21,34] The @fibR@ function is not synthesizable by the Clash compiler, because, when we take a /structural/ view, @fibR@ describes an infinitely deep structure. In principal, descriptions like the above could be synthesized to a circuit, but it would have to be a /sequential/ circuit. Where the most general synthesis would then require a stack. Such a synthesis approach is also known as /behavioral/ synthesis, something which the Clash compiler simply does not do. One reason that Clash does not do this is because it does not fit the paradigm that only functions working on values of type 'Signal' result in sequential circuits, and all other (non higher-order) functions result in combinational circuits. This paradigm gives the designer the most straightforward mapping from the original Haskell description to generated circuit, and thus the greatest control over the eventual size of the circuit and longest propagation delay. * __Value-recursion__ As demonstrated in this definition of a function that calculates the n'th Fibbonaci number on the n'th clock cycle: @ fibS :: SystemClockResetEnable => Signal System (Unsigned 64) fibS = r where r = 'register' 0 r + 'register' 0 ('register' 1 r) @ To get the first 10 numbers, we do the following: >>> sampleN @System 11 fibS [0,0,1,1,2,3,5,8,13,21,34] Unlike the @fibR@ function, the above @fibS@ function /is/ synthesizable by the Clash compiler. Where the recursively defined (non-function) value /r/ is synthesized to a feedback loop containing three registers and one adder. Note that not all recursively defined values result in a feedback loop. An example that uses recursively defined values which does not result in a feedback loop is the following function that performs one iteration of bubble sort: @ sortVL xs = 'map' fst sorted ':<' (snd ('last' sorted)) where lefts = 'head' xs :> map snd ('init' sorted) rights = 'tail' xs sorted = 'zipWith' compareSwapL ('lazyV' lefts) rights @ Where we can clearly see that @lefts@ and @sorted@ are defined in terms of each other. Also the above @sortV@ function /is/ synthesizable. * __Static/Structure-dependent recursion__ Static, or, structure-dependent recursion is a rather /vague/ concept. What we mean by this concept are recursive definitions where a user can sensibly imagine that the recursive definition can be completely unfolded (all recursion is eliminated) at compile-time in a finite amount of time. Such definitions would e.g. be: @ mapV :: (a -> b) -> Vec n a -> Vec n b mapV _ Nil = Nil mapV f (Cons x xs) = Cons (f x) (mapV f xs) topEntity :: Vec 4 Int -> Vec 4 Int topEntity = mapV (+1) @ Where one can imagine that a compiler can unroll the definition of @mapV@ four times, knowing that the @topEntity@ function applies @mapV@ to a 'Vec' of length 4. Sadly, the compile-time evaluation mechanisms in the Clash compiler are very poor, and a user-defined function such as the @mapV@ function defined above, is /currently/ not synthesizable. We /do/ plan to add support for this in the future. In the mean time, this poor support for user-defined recursive functions is amortized by the fact that the Clash compiler has built-in support for the higher-order functions defined in "Clash.Sized.Vector". Most regular design patterns often encountered in circuit design are captured by the higher-order functions in "Clash.Sized.Vector". * __Recursive datatypes__ The Clash compiler needs to be able to determine a bit-size for any value that will be represented in the eventual circuit. More specifically, we need to know the maximum number of bits needed to represent a value. While this is trivial for values of the elementary types, sum types, and product types, putting a fixed upper bound on recursive types is not (always) feasible. This means that the ubiquitous list type is unsupported! The only recursive types that are currently supported by the Clash compiler is the 'Vec'tor and 'RTree' types, for which the compiler has hard-coded knowledge. For \"easy\" 'Vec'tor literals you should use Template Haskell splices and the 'listToVecTH' /meta/-function that as we have seen earlier in this tutorial. * __GADTs__ Clash has experimental support for GADTs. Similar to recursive types, Clash can't determine bit-sizes of GADTs. Notable exceptions to this rule are 'Vec' and 'RTree'. You can still use your own GADTs, as long as they can be removed through static analysis. For example, the following case will be optimized away and is therefore fine to use: @ x = case 'resetKind' @'System' of SAsynchronous -> \'a\' SSynchronous -> \'b\' @ * __Floating point types__ There is no support for the 'Float' and 'Double' types, if you need numbers with a /fractional/ part you can use the 'Fixed' point type. As to why there is no support for these floating point types: 1. In order to achieve reasonable operating frequencies, arithmetic circuits for floating point data types must be pipelined. 2. Haskell's primitive arithmetic operators on floating point data types, such as 'plusFloat#' @ __plusFloat#__ :: 'Float#' -> 'Float#' -> 'Float#' @ which underlie @'Float'@'s 'Num' instance, must be implemented as purely combinational circuits according to their type. Remember, sequential circuits operate on values of type \"@'Signal' a@\". Although it is possible to implement purely combinational (not pipelined) arithmetic circuits for floating point data types, the circuit would be unreasonable slow. And so, without synthesis possibilities for the basic arithmetic operations, there is no point in supporting the floating point data types. * __Haskell primitive types__ Only the following primitive Haskell types are supported: * 'Integer' * 'Int' * 'Int8' * 'Int16' * 'Int32' * 'Int64' (not available when compiling with @-fclash-intwidth=32@ on a 64-bit machine) * 'Word' * 'Word8' * 'Word16' * 'Word32' * 'Word64' (not available when compiling with @-fclash-intwidth=32@ on a 64-bit machine) * 'Char' There are several aspects of which you should take note: * 'Int' and 'Word' are represented by the same number of bits as is native for the architecture of the computer on which the Clash compiler is executed. This means that if you are working on a 64-bit machine, 'Int' and 'Word' will be 64-bit. This might be problematic when you are working in a team, and one designer has a 32-bit machine, and the other has a 64-bit machine. In general, you should be avoiding 'Int' in such cases, but as a band-aid solution, you can force the Clash compiler to use a specific bit-width for `Int` and `Word` using the @-fclash-intwidth=N@ flag, where /N/ must either be /32/ or /64/. * When you use the @-fclash-intwidth=32@ flag on a /64-bit/ machine, the 'Word64' and 'Int64' types /cannot/ be translated. This restriction does /not/ apply to the other three combinations of @-fclash-intwidth@ flag and machine type. * The translation of 'Integer' is not meaning-preserving. 'Integer' in Haskell is an arbitrary precision integer, something that cannot be represented in a statically known number of bits. In the Clash compiler, we chose to represent 'Integer' by the same number of bits as we do for 'Int' and 'Word'. As you have read in a previous bullet point, this number of bits is either 32 or 64, depending on the architecture of the machine the Clash compiler is running on, or the setting of the @-fclash-intwidth@ flag. Consequently, you should use `Integer` with due diligence; be especially careful when using `fromIntegral` as it does a conversion via 'Integer'. For example: > signedToUnsigned :: Signed 128 -> Unsigned 128 > signedToUnsigned = fromIntegral can either lose the top 64 or 96 bits depending on whether 'Integer' is represented by 64 or 32 bits. Instead, when doing such conversions, you should use 'bitCoerce': > signedToUnsigned :: Signed 128 -> Unsigned 128 > signedToUnsigned = bitCoerce * __Side-effects: 'IO', 'ST', etc.__ There is no support for side-effecting computations such as those in the 'IO' or 'ST' monad. There is also no support for Haskell's <http://www.haskell.org/haskellwiki/Foreign_Function_Interface FFI>. -} {- $vslava In Haskell land the most well-known way of describing digital circuits is the Lava family of languages: * <http://hackage.haskell.org/package/chalmers-lava2000 Chalmers Lava> * <http://hackage.haskell.org/package/xilinx-lava Xilinx Lava> * <http://hackage.haskell.org/package/york-lava York Lava> * <http://hackage.haskell.org/package/kansas-lava Kansas Lava> The big difference between Clash and Lava is that Clash uses a \"standard\" compiler (static analysis) approach towards synthesis, where Lava is an embedded domain specific language. One downside of static analysis vs. the embedded language approach is already clearly visible: synthesis of recursive descriptions does not come for \"free\". This will be implemented in Clash in due time, but that doesn't help the circuit designer right now. As already mentioned earlier, the poor support for recursive functions is amortized by the built-in support for the higher-order in "Clash.Sized.Vector". The big upside of Clash and its static analysis approach is that Clash can do synthesis of \"normal\" functions: there is no forced encasing datatype (often called /Signal/ in Lava) on all the arguments and results of a synthesizable function. This enables the following features not available to Lava: * Automatic synthesis for user-defined ADTs * Synthesis of all choice constructs (pattern matching, guards, etc.) * 'Applicative' instance for the 'Signal' type * Working with \"normal\" functions permits the use of e.g. the 'Control.Monad.State.Lazy.State' monad to describe the functionality of a circuit. Although there are Lava alternatives to some of the above features (e.g. first-class patterns to replace pattern matching) they are not as \"beautiful\" and / or easy to use as the standard Haskell features. -} {- $migration * Clash has overhauled the way synthesis options are represented. You can read about this change in the blogpost: <https://clash-lang.org/blog/0005-synthesis-domain/ New feature: configurable initial values>. The executive summary is as follows: +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | __0.99__ | __1.0__ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @topEntity (clk::Clock d 'Source) rst = withClockReset f clk rst@ | @topEntity clk rst = withClockResetEnable clk rst enableGen f@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @topEntity (clk::Clock d 'Gated) rst = withClockReset f clk rst@ | @topEntity clk rst enable = withClockResetEnable clk rst enable f@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @data A = ... @ (and @A@ is used as state, for example in register or mealy) | @data A = ... deriving (Generic,NFDataX)@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @SystemClockReset@ | @SystemClockResetEnable@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @HiddenClockReset dom gated sync@ | @HiddenClockResetEnable dom@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @HiddenClock dom gated@ | @HiddenClock dom@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @HiddenReset dom sync@ | @HiddenReset dom@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @Clock dom gated@ | @Clock dom@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ | @Reset dom sync@ | @Reset dom@ | +------------------------------------------------------------------------------+--------------------------------------------------------------------+ * @outputVerifier@ now operates on two domains. If you only need one, simply change it to @outputVerifier'@ * For an overview of all other changes, check out <https://github.com/clash-lang/clash-compiler/blob/1.0/clash-ghc/CHANGELOG.md the changelog> === Examples ==== FIR filter FIR filter in Clash 0.99: @ module FIR where import Clash.Prelude import Clash.Explicit.Testbench dotp :: SaturatingNum a => Vec (n + 1) a -> Vec (n + 1) a -> a dotp as bs = fold boundedPlus (zipWith boundedMult as bs) fir :: (Default a, KnownNat n, SaturatingNum a, HiddenClockReset domain gated synchronous) => Vec (n + 1) a -> Signal domain a -> Signal domain a fir coeffs x_t = y_t where y_t = dotp coeffs \<$\> bundle xs xs = window x_t topEntity :: Clock System Source -> Reset System Asynchronous -> Signal System (Signed 16) -> Signal System (Signed 16) topEntity = exposeClockReset (fir (2:>3:>(-2):>8:>Nil)) {\-\# NOINLINE topEntity \#-\} testBench :: Signal System Bool testBench = done where testInput = stimuliGenerator clk rst (2:>3:>(-2):>8:>Nil) expectedOutput = outputVerifier clk rst (4:>12:>1:>20:>Nil) done = expectedOutput (topEntity clk rst testInput) clk = tbSystemClockGen (not \<$\> done) rst = systemResetGen @ FIR filter in Clash 1.0: @ module FIR where import Clash.Prelude import Clash.Explicit.Testbench dotp :: 'SaturatingNum' a => 'Vec' (n + 1) a -> 'Vec' (n + 1) a -> a dotp as bs = 'fold' 'boundedAdd' ('zipWith' 'boundedMul' as bs) fir :: ( 'HiddenClockResetEnable' dom , 'KnownNat' n , 'SaturatingNum' a , 'NFDataX' a , 'Default' a ) => 'Vec' (n + 1) a -> 'Signal' dom a -> 'Signal' dom a fir coeffs x_t = y_t where y_t = dotp coeffs \<$\> 'bundle' xs xs = 'window' x_t topEntity :: 'Clock' 'System' -> 'Reset' 'System' -> 'Enable' 'System' -> 'Signal' 'System' ('Signed' 16) -> 'Signal' 'System' ('Signed' 16) topEntity = 'exposeClockResetEnable' (fir (2:>3:>(-2):>8:>'Nil')) {\-\# NOINLINE topEntity \#-\} testBench :: 'Signal' 'System' 'Bool' testBench = done where testInput = 'stimuliGenerator' clk rst (2:>3:>(-2):>8:>'Nil') expectedOutput = 'outputVerifier'' clk rst (4:>12:>1:>20:>'Nil') done = expectedOutput (topEntity clk rst 'enableGen' testInput) clk = 'tbSystemClockGen' (not \<$\> done) rst = 'systemResetGen' @ ==== Blinker circuit Blinker circuit in Clash 0.99: @ {\-\# LANGUAGE NoMonoLocalBinds \#-\} module Blinker where import Clash.Prelude import Clash.Promoted.Symbol import Clash.Intel.ClockGen type Dom50 = Dom \"System\" 20000 {\-\# ANN topEntity (Synthesize { t_name = \"blinker\" , t_inputs = [ PortName \"CLOCK_50\" , PortName \"KEY0\" , PortName \"KEY1\" ] , t_output = PortName \"LED\" }) \#-\} topEntity :: Clock Dom50 Source -> Reset Dom50 Asynchronous -> Signal Dom50 Bit -> Signal Dom50 (BitVector 8) topEntity clk rst = exposeClockReset (mealy blinkerT (1,False,0) . isRising 1) pllOut rstSync where (pllOut,pllStable) = altpll \@Dom50 (SSymbol \@\"altpll50\") clk rst rstSync = resetSynchronizer pllOut (unsafeToAsyncReset pllStable) blinkerT (leds,mode,cntr) key1R = ((leds',mode',cntr'),leds) where -- clock frequency = 50e6 (50 MHz) -- led update rate = 333e-3 (every 333ms) cnt_max = 16650000 -- 50e6 * 333e-3 cntr' | cntr == cnt_max = 0 | otherwise = cntr + 1 mode' | key1R = not mode | otherwise = mode leds' | cntr == 0 = if mode then complement leds else rotateL leds 1 | otherwise = leds @ Blinker in Clash 1.0: @ module Blinker where import "Clash.Signal" import "Clash.Prelude" import "Clash.Intel.ClockGen" 'createDomain' vSystem{vName=\"DomInput\", vPeriod=20000} 'createDomain' vSystem{vName=\"Dom100\", vPeriod=10000} topEntity :: Clock DomInput -> Signal DomInput Bool -> Signal Dom100 Bit -> Signal Dom100 (BitVector 8) topEntity clk rst = 'exposeClockResetEnable' ('mealy' blinkerT (1,False,0) . Clash.Prelude.isRising 1) pllOut rstSync 'enableGen' where (pllOut,pllStable) = 'Clash.Intel.ClockGen.altpll' \@Dom100 (SSymbol \@\"altpll100\") clk ('Clash.Signal.unsafeFromLowPolarity' rst) rstSync = 'Clash.Signal.resetSynchronizer' pllOut ('Clash.Signal.unsafeFromLowPolarity' pllStable) blinkerT (leds,mode,cntr) key1R = ((leds',mode',cntr'),leds) where -- clock frequency = 100e6 (100 MHz) -- led update rate = 333e-3 (every 333ms) cnt_max = 'maxBound' :: ('Index' 33300000) -- 100e6 * 333e-3 cntr' | cntr == cnt_max = 0 | otherwise = cntr + 1 mode' | key1R = not mode | otherwise = mode leds' | cntr == 0 = if mode then complement leds else rotateL leds 1 | otherwise = leds @ -}