[Libre-soc-dev] [RFC] REMAP, SHAPE, complex (full) FFT

[Luke Kenneth Casson Leighton]

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crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

On Sat, Jul 10, 2021 at 11:46 PM Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:

> 1) the current svremap, create a new "setvl-with-remap-butterfly-for-FFT"
>     instruction, to be merged with the functionality of setvl.

still TODO.  should be easy now that the SVSHAPEs are independent from
SVREMAP.

> 2) a new SPR, called SVREMAP, whose format and purpose would be to set
>     what is currently established in REMAP "propagation"
>     https://libre-soc.org/openpower/sv/propagation/

done, very simple, stores its immediates into the SVREMAP SPR:
https://libre-soc.org/openpower/isa/simplev/

the principle here is:

* there are 5 registers - 3 input ([F]RA, [F]RB, [F]RC) 2 output
(RT/FRT, EA/FRS)
* there are 4 SVSHAPEs (0-3)
* REMAP is a dead-simple table "FRA uses SVSHAPEn, FRB uses SVSHAPEm ..."

that's now implemented and the unit tests for FFT and Matrix-Mul updated.

the next important step will be to check that temporary (scalar)
registers can be
used in a full complex FFT, with the "REMAPped" vector registers not needing
too many "remap" instructions.

l.