[Libre-soc-dev] demo of 16/32/48/64-bit LE/BE backward-compatible encoding

Luke Kenneth Casson Leighton lkcl at lkcl.net
Thu Nov 26 02:05:19 GMT 2020

On 11/26/20, Jacob Lifshay <programmerjake at gmail.com> wrote:
> I added colors to the demo encoding, hopefully making it easier to follow:
> https://libre-soc.org/openpower/sv/16_bit_compressed/demo/
> I had to use CSS classes defined in the local.css file to get colors,
> since the markdown renderer filters out style attributes but keeps
> class attributes.


right.  ok.  sooo.... the 48bit encoding is the one that i spotted is
weird, and, critically, is dependent on whether pc mod 4 is 0 or 2.

also, it would be good to confirm for LE mode that:

* when pc mod 4 == 0 it is byte offs 3 that identifies the EXTNNN
* when pc mod 4 == 2 it is byte offs 1

if you can add a background colour that highlights those conditions
(for the byte with the EXTNNN in it) it would make things clearer.

that would show, as i learned by the bits of paper in the video, that
SV-P48 needs to be encoded *differently* depending on whether it
starts from byte 2 or on byte 0.


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