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Vector TG minutes from 2020/11/6 meeting


Krste Asanovic
 

Also, reminder we'll be meeting tomorrow (Friday Nov 13) as per
calendar entry (7 hours from now),

Krste

Date: 2020/11/06
Task Group: Vector Extension
Chair: Krste Asanovic
Co-Chair: Roger Espasa
Number of Attendees: ~18
Current issues on github: https://github.com/riscv/riscv-v-spec

Issues discussed:

#592 "Heritage" - old prior art

We discussed how to add notes showing known older designs that had
same features as included in spec, and spent some time covering all
details in spec. We cannot discuss live patents in meetings, but we
can describe public domain techniques from 20+ years ago. Proposal is
to accept pull requests with details incorporated as NOTE comments for
now. Should ideally format differently than other commentary, but
this can be done later.

(#529) Whole register load/store misalignment exceptions

While we had previously agreed (#529) that whole register load/stores
could report misalignment exceptions if the base address was not
aligned with the encoded hint EEW, we had not considered cases where
the machine did not support smaller EEWs. In particular, stores are
always encoded with EEW=8.

We rejected allowing machines to report exceptions if not
VLEN-aligned, as this would complicate stack save/restore in ABIs with
smaller stack alignments.

We decided to stay with current text that allows misaligned exceptions
to be reported according to greater of the smallest supported EEW or
the encoded EEW. Profiles can mandate support for certain EEWs.