[Libre-soc-dev] compressed instructions state requirements

[Jacob Lifshay]

On Wed, Nov 25, 2020, 17:52 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
wrote:

> On 11/26/20, Jacob Lifshay <programmerjake at gmail.com> wrote:
> > On Wed, Nov 25, 2020, 15:32 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
> > wrote:
> >
> >> give it 30-40 minutes to complete upload and processing...
> >> https://youtu.be/LdAIOew63Bs
> >
> >
> > Watched it, it looks like a correct description of Standard Mode :)
>
> the realisation hit me that actually, what you do is, simply use PC[1]
> as the lookup of where to find EXTNNN, but from the right, not the
> left:
>
>     ext_idx_lookup_byte = 3-PC[1]*2
>

:) it works for all 16-bit parts in a instruction, not just the one with
the primary opcode.

>
> 48bit is the only spectacular weirdness and luckily we're in charge of
> defining that.
>

48bit isn't that weird, just think of it as a 32-bit instruction followed
by a 16-bit instruction. you lay out the bytes in exactly the same way.

Jacob