[Libre-soc-dev] "sandbox" SPRs for SV

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sun Jan 31 14:57:27 GMT 2021

paul, hi,

ahh i just read the v3.1B p12 bit about sandbox SPRs:

   The designated SPR sandbox consists of non-privileged SPRs 704-719
and privileged SPRs 720-735.

that's 16 in each batch.  to which my reaction is, "err whoops" :)
for the "full" features of SV, introduced over time, we may need
around 32 to 48 SPRs (replication of quite a lot of state for
supervisor, hypervisor).

context propagation alone i expected to implement QTY 8 32-bit SPRs,
with room for long-term future implementations to expand that to 16:

these contexts basically allow hardware compression of 64-bit
OpenPOWER ISA *including* (potentially, if it's done carefully) v3.1B
prefixes, by separating out the prefix from the suffix and applying
the prefix when the LSB of an internal shift register hits a "1".

can i ask: is there an alternative reserved area that can be made available?


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

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