clash-prelude-0.99.3: CAES Language for Synchronous Hardware - Prelude library

Clash.Explicit.Synchronizer

Description

Synchronizer circuits for safe clock domain crossings

Synopsis

Bit-synchronizers

Arguments

 :: Clock domain1 gated1 Clock to which the incoming data is synchronised -> Clock domain2 gated2 Clock to which the outgoing data is synchronised -> Reset domain2 synchronous Reset for registers on the outgoing domain -> a Initial value of the two synchronisation registers -> Signal domain1 a Incoming data -> Signal domain2 a Outgoing, synchronised, data

Synchroniser based on two sequentially connected flip-flops.

• NB: This synchroniser can be used for bit-synchronization.
• NB: Although this synchroniser does reduce metastability, it does not guarantee the proper synchronisation 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-synchronisation use asyncFIFOSynchronizer.

Word-synchronizers

Arguments

 :: 2 <= addrSize => SNat addrSize Size of the internally used addresses, the FIFO contains 2^addrSize elements. -> Clock wdomain wgated Clock to which the write port is synchronised -> Clock rdomain rgated Clock to which the read port is synchronised -> Reset wdomain synchronous -> Reset rdomain synchronous -> Signal rdomain Bool Read request -> Signal wdomain (Maybe a) Element to insert -> (Signal rdomain a, Signal rdomain Bool, Signal wdomain Bool) (Oldest element in the FIFO, empty flag, full flag)

Synchroniser 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 synchroniser can be used for word-synchronization.