Documentation

tutorial for System.Readpitaya Libraray

System.Readpitaya is native haskell library for redpitaya that enables direct bindings on FPGA. This library is aimed to run on redpitaya and is inteded for use with crosscompiler.

To build and run code and examples you need cross-ghc compiler for armel processor.

Here it is simpel an minimal example to use library

import System.RedPitaya.Fpga

main = withOpenFpga (setLed 0x55) 

withOpenFpga is function, that takes Fpga operation and executes it. It handels opening and closing of FPGA resources so it is advisable that that all operation are executed inside and withOpenFpga gets called only once.

If you take look of prototype setLed you can see that it has protype setLed :: Registry -> Fpga () And that can be understand that it takes Registy (that is 32 bit unsigned integer) and returns Fpga (). Fpga a is type that can run in withOpenFpga function. () is empty or void value that is retured after setLed gets called. What setLed does it takes writes registry value at apropriate addres in fpga registry map described in document FPGA metioned in first section.

In our next example we will build program that displays value that is written in this registry using function getLed

import System.RedPitaya.Fpga
import Numeric (showHex)

main = do
    reg <- withOpenFpga getLed
    putStrLn ( show reg)

here reg is value can get "get" from withOpenFpga. Function withOpenFpga has prototype of 'Fpga a -> IO a'. That mean that returns same value as it is returned from executing last command executed in block. In our case that is just function getLed. Since getLed :: Fpga Registry that mean that ir returns Fpga Registry type.

IO Registry (a in definition of withOpenFpga becomes Registry). We haven't mentioned IO a before but that is type one can execute commands like putStrLn with.

import System.RedPitaya.Fpga
import Numeric (showHex)

main = do
    reg <- withOpenFpga ( do
                            setLed 0x44
                            r <- getLed
                            return r
                        )
    putStrLn ( show reg )

This code runs two do blocks. One handles IO type where types IO a are running and other do block with type 'Fpga a'. If one needs to run IO types inside Fpga block he/she needs to change IO type to Fpga type using function liftIO.

import System.RedPitaya.Fpga
import Numeric (showHex)
import Control.Monad.IO.Class (liftIO)

main = do
    withOpenFpga $ do
            setLed 0x44
            reg <- getLed 
            liftIO $ putStrLn $ show reg
    putStrLn "done"

In this example we also use build in operator $ that works as a brackets to to the end.

liftIO $ putStrLn $ showHex reg "" 
-- is same as
liftIO ( putStrLn ( showHex reg "" ))

If you like to know more about operator $ or any other standard functions used, you can use invaluable search engine Hoogle where is link on haddock manuals with description and link to source code. Similar search engines are also availabe at Hayoo! and Stackage.

Lets do some more tricks with diodes and using standard

import System.RedPitaya.Fpga
import Control.Concurrent (threadDelay)
import Data.Bits
import Control.Monad.IO.Class (liftIO)

knightRider n = do
    let ledn = 1 + abs ((mod n 12) - 6) -- 6,5,4,3,2,1,2,3,4,5,6,7,6,5,4,3,2,1,2,3,4,5,6,7,6,5...
    setLed ( shiftL 1 ledn )
    liftIO ( threadDelay (30000) )
    knightRider (n + 1)

main = withOpenFpga (knightRider 0)

knightRider is function that gets caled each time with next integer.ledn in generated in way that provides numbering in apropriate order. shiftL function . Next threadDelay delays execution, by 30000 microseconds and since nightRider runs inside withOpenFpga we have to use liftIO just to make type compatible. Finaly we call nightRider with next number and whole procees repeats.

So far we covered lot if of stuff on how to use this library. Even though all examples were reading and writing to led registry you can be sure that all function provided by library that has type signature Registry -> Fpga () works and can be used just like setLed and all functions with type signature Fpga Registry works like getLed.