[libre-riscv-dev] buffered pipeline

[Luke Kenneth Casson Leighton]

On Fri, Mar 15, 2019 at 2:04 AM Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:

> > I greatly prefer to use something other than stb or strobe for the name as
> > I find stb to be totally unintuitive and strobe to be somewhat unintuitive.
> > i'm perfectly fine switching to ready and valid; if chisel uses
> > ready/valid, it's widespread enough that I don't think anyone reading it
> > for the first time will have trouble understanding it.
>
>  yeah i like it.  hmm, ready is the inversion of busy, that's ok
> though.  will update the buffered version accordingly.

oof.  that was slightly mind-bending, luckily it was straightforward
and mundane.  i'm also a bit eye-glazed from writing an article for
linuxjournal, 6000 words in 3 and a half hours non-stop... bleh :)

i took the opportunity to split out two classes IOAckIn and IOAckOut,
the reason for keeping them being that if the class names were the
same (because the signals named ready and valid were the same), the
opportunity to discern them with prefixes "p_" for "previous stage
connection" and "n_" for "connected to next stage" would be lost.

btw, jacob, i notice that in the class "Stage", you manually postfix
the name of the StageInput.  in the manner in which you've created the
layout, nmigen automatically creates a name prefix, using underscores,
based on the name of the class instance member variable that the
signal is in.

this name filters through to the verilog output, automatically.

so in the case of the Stage instance, which has a StageOutput instance
member, when the signal named "sending" is created, it would be
*automatically* named "output_sending".

the removal of the manual creation of names would remove a lot of
cruft from the code, making it simpler and easier to read.

also, reset=0 is the default, and the width defaults to 1 as well.
thus, overall:

        self._data_valid = Signal(1, name=name + "_data_valid", reset=0)

can therefore be replaced with:

        self._data_valid = Signal()

that's it.  that's all that's needed.

l.