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

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Fri Aug 28 20:12:14 BST 2020


Cole Poirier <colepoirier at gmail.com> changed:

           What    |Removed                     |Added
                 CC|                            |colepoirier at gmail.com

--- Comment #7 from Cole Poirier <colepoirier at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #4)
> https://git.libre-soc.org/?p=libresoc-isa-manual.git;a=blob;f=powerpc-add/
> src/SVPrefix.tex;hb=HEAD
> it occurred to me that if we were to do SVPrefix by examining the fields.txt
> and the Forms, we would literally be at it forever.
> the technique developed by the microwatt team, to create micro-ops, has
> *already*
> done that analysis, and we hold that information in CSV files.
> therefore if we instead do the analysis of which prefix is needed based on
> the *CSV* files we save a vast amount of time.
> it may also be possible to partially (or completely) automate the process
> of determining the prefixes.

(In reply to Luke Kenneth Casson Leighton from comment #6)
> (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
> Pointer"

Ooh very cool/exciting, I can't wait to see how this develops into final form.

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