| Copyright | (C) 2019 Myrtle Software Ltd |
|---|---|
| License | BSD2 (see the file LICENSE) |
| Maintainer | Christiaan Baaij <christiaan.baaij@gmail.com> |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Clash.Prelude.Synchronizer
Description
Synchronizer circuits for safe clock domain crossings
Synopsis
- dualFlipFlopSynchronizer :: (Undefined a, HiddenClock dom1, HiddenClockResetEnable dom2) => a -> Signal dom1 a -> Signal dom2 a
- asyncFIFOSynchronizer :: (HiddenClockResetEnable rdom, HiddenClockResetEnable wdom, 2 <= addrSize) => SNat addrSize -> Signal rdom Bool -> Signal wdom (Maybe a) -> (Signal rdom a, Signal rdom Bool, Signal wdom Bool)
Bit-synchronizers
dualFlipFlopSynchronizer Source #
Arguments
| :: (Undefined a, HiddenClock dom1, HiddenClockResetEnable dom2) | |
| => a | Initial value of the two synchronization registers |
| -> Signal dom1 a | Incoming data |
| -> Signal dom2 a | Outgoing, synchronized, data |
Synchronizer based on two sequentially connected flip-flops.
- NB: This synchronizer can be used for bit-synchronization.
NB: Although this synchronizer does reduce metastability, it does not guarantee the proper synchronization of a whole word. For example, given that the output is sampled twice as fast as the input is running, and we have two samples in the input stream that look like:
[0111,1000]
But the circuit driving the input stream has a longer propagation delay on msb compared to the lsbs. What can happen is an output stream that looks like this:
[0111,0111,0000,1000]
Where the level-change of the msb was not captured, but the level change of the lsbs were.
If you want to have safe word-synchronization use
asyncFIFOSynchronizer.
Word-synchronizers
asyncFIFOSynchronizer Source #
Arguments
| :: (HiddenClockResetEnable rdom, HiddenClockResetEnable wdom, 2 <= addrSize) | |
| => SNat addrSize | Size of the internally used addresses, the FIFO contains |
| -> 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, |
Synchronizer implemented as a FIFO around an asynchronous RAM. Based on the design described in Clash.Tutorial, which is itself based on the design described in http://www.sunburst-design.com/papers/CummingsSNUG2002SJ_FIFO1.pdf.
NB: This synchronizer can be used for word-synchronization.