[Libre-soc-dev] v3.1B prefix

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sat Dec 5 20:22:55 GMT 2020

On 12/5/20, Alexandre Oliva <oliva at gnu.org> wrote:
> On Dec  5, 2020, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>> consequently, the implications are that, even more severely limited as
>> it is, the 24 bit v3.1b prefix system is... well... our only realistic
>> "least bad" option for now.
> Sorry for being dense again, but...  does this imply that 16-bit
> compressed-mode is out too?

that's what i'm advocating, yes.  a 10bit (or 11bit if using 2 major
opcodes) still makes sense but the whole FSM switching and ABIs is
just too much.

> As in, does it still make any sense for me to get back to the
> compression estimator, which I was going to return to as soon as I was
> done with email?

yes funnily enough it does because the 16 bit ISA still needs
statistical analysis for forming SV-P32.

remember, i said, SV-P32 would be:

* 11 bit SV prefix
* -->> 16 bit instruction based on C <<--

this was always planned: it's the *stand-alone* C that is not viable.

plus, a statistical analysis of *just* the 10bit would also be useful.

and a hell of a lot simpler to do.


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