[libre-riscv-dev] [Bug 336] ALU CompUnit needs to recognise that RA (src1) can be zero

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=336

--- Comment #54 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Cesar Strauss from comment #53)
> commit 71a791cf5f05bd5858fdc60f4ccdca936edc1d75
> Author: Cesar Strauss <cestrauss at gmail.com>
> Date:   Sun Jun 7 16:32:11 2020 -0300
> 
>     Make the test ALU conform to the valid/ready protocol
>     
>     Adjust the test case accordingly.
> 
> It was definitively not a one-line change. But it was fun.

oh good! :)

> Select any other operation than MUL, ADD, or SHR, and it will do a
> combinatorial subtraction, with zero-delay and no registering.
> 
> The interesting thing about zero-delay is that, due to the absence of an
> internal register, it will not release the input data until the result is
> transferred out.

oh wait... that's a *combinatorial* ALU?  iinteresting.  i wonder
what that could be used for.

hmmm i tried putting OP_NOP in there, and both compunit1 and parallel
locked up.  this tends to indicate a combinatorial loop.  any clues?


> Basically, the handshake signals of the input and output ports are directly
> connected between them, only the data is modified between the ports.
> 
> Nice change, working with RTL again. Will go back to the parallel unit
> tests, now.

:)

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