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

Jacob Lifshay programmerjake at gmail.com
Thu Dec 3 23:47:45 GMT 2020

On Thu, Dec 3, 2020, 15:40 Luke Kenneth Casson Leighton <lkcl at lkcl.net>

> jacob, hi,
> i was going to write paul a message yesterday, summarising that we
> need 24 bits for SVP and so started looking at v3.1B 64 bit for the
> first time.
> the first thing that struck me was: the entirety of the EXT01 range is
> used up with 4 formats, 2 bits to identify each.  one for LD/ST, and
> so on.
> the next puzzling part was, ok so if the EXT01 area contains nothing
> (no opcodes), how the heck does it work? so i went to the Opcode Map
> in the appendix and found a prefix/suffix map.
> this apparently says that you should look at the *other* EXTNNN to
> determine the instruction.  which makes sense.
> here then there are some major opcodes marked reserved (only around 6
> or so), 60 to 70% are blank, some have "redefined" meanings (Major 132
> for example), some are entire rows.

See https://libre-soc.org/openpower/sv/svp_rewrite/svp64/ for a WIP version
of SVP64, it should explain/answer some of your questions.


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