[Libre-soc-isa] [Bug 213] SimpleV Standard writeup needed

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Fri Aug 28 15:25:08 BST 2020


--- Comment #6 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #5)
> the chosen prefixes should mesh well with the 64-bit instructions that were
> added in v3.1 of the spec.

unfortunately that is very unlikely.  we need *eight* major opcodes in order to
fit POWER-Compressed, SVP32, SVP48, SVP64 and VBLOCK.

before the v3.1 spec additions there were only 8 spare major opcodes.

the 6 bits of POWER major opcodes only leaves 10 bits for SVP32 and SVP48. this
is not enough: we need 11.

or, we allow opcode 1 but sacrifice POWER-Compressed which puts it under even
more pressure than it already is.

i have a much more effective scheme than v3.1 prefixing, called a "Data

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