dmcq (dmcq.delete@this.fano.co.uk) on March 30, 2021 3:28 pm wrote:
> Jon Masters (jcm.delete@this.jonmasters.org) on March 30, 2021 11:41 am wrote:
> > https://www.arm.com/why-arm/architecture/cpu
> >
>
> I wonder if they'll continue producing ARMv8 Cortex cores without some of the new facilities for smartphones.
> SVE2 is great for instance - but using it would make software incompatible with current phones - so
> I can see there being a bit of resistance if there is any appreciable extra silicon used.
>
> I see they're dropping system level support for 32 bit code, and about time
> too I think, but that would mean pain if one wanted an ARMv9 Raspberry Pi :-)

Your logic about the compability goes totally backwards.
ARMv9 is backwards compatible with ARMv8. New ARMv9 cores run all ARMv8 software.

Zero reason to use old ARMv8 for compatibility, on the other hand, with even a slow and narrow SVE2 implmentaion, ALL future SVE2 code will work. Exactly because of compatility reason we will want to move to SVE2-supporting CPUs ASAP.

And 128-bit SVE2 implementation will not be much bigger than NEON implementation. Area is not a reason to leave it out.