[Arm-netbook] Libre RISC-V SoC

[Lauri Kasanen]

On Fri, 19 Jan 2018 16:06:51 +0000
Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:

> so he asked, also, what would it take to get things ready within a
> year, to hand over the ASIC-based design to MOSIS, for them to turn it
> into an ASIC, and i said "a team of engineers would need to be paid
> for".  he asked - and please note the question very carefully - "would
> USD 250,000 be enough?" to which i replied (genuinely) yes... if done
> carefully.  software also has to be taken care of.

A libre risc-v soc would indeed be great.

> we worked out that if you put in 2 nyuzi
> cores and managed to halve the number of instructions / pixel by
> replacing critical path blocks with hardware-rendering ones, you'd end
> up at about 25% the performance of MALI400 and that i feel would be
> "good enough" for a first version.  i'd be interested to hear what
> people think, here.

25% of MALI400 is not enough for even mobile games: it is enough for
spinning windows ala Compiz, but that can also be done with much less.
So if the goal is something usable, rather than a platform to kickstart
nyuzi development on, targeting lower perf with lower power usage would
be better.

Now, I don't remember if video decode blocks would be in the RISC parts
or in nyuzi. GPUs are usually good at colorspace conversion and
scaling, so if there are no dedicated blocks for those, then the nyuzi
core should be targeted/sized at that usage. Bicubic upscaling + color
conversion to fullhd - the texture units, memory bandwidth and compute
parts need to have enough oomph.

Radeon R300 parts are capable of that. I'm not sure how that maps to %
of Mali.

- Lauri