[libre-riscv-dev] MultiCompUnit- ALU interaction. was: daily kan-ban update 30may2020

[Luke Kenneth Casson Leighton <lkcl@lkcl.net>]

On Saturday, May 30, 2020, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
wrote:

>
> > * more on ALU to MultiCompUnit.
> >
> > i *do not* know what i am doing, here.  the time dependent signalling is
> critical and could take several days to weeks to get right.
>
> a simple bug where XER so and ca were swapped as inputs masked efforts
> to get the interaction working.  no point trying to debug against a
> target with multiple unknowns, any one of which causes the entire test
> to fail.
>
> progress should be better, now.


we are reeeaally damn lucky.

i managed to get at least something running.  it failed only because one
operation required one operand (exts).  this leaves the CU waiting for RB
which never gets activated.

we are going to have to make a couple of modifications:

1. a "read mask".  this will tell the CompUnit that some operands are not
required.

2. a "write mask" which actually already exists (Data.ok) for output
results to also be optional.

l.



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