From: Luke Kenneth Casson Leighton Date: Thu, 26 Apr 2018 08:59:06 +0000 (+0100) Subject: start filling in X-Git-Tag: convert-csv-opcode-to-binary~5490 X-Git-Url: https://git.libre-soc.org/?p=libreriscv.git;a=commitdiff_plain;h=8b6f3f00d664754f87cf540dc5756d91c16e1423 start filling in --- diff --git a/isa_conflict_resolution.mdwn b/isa_conflict_resolution.mdwn index 9389c116b..d2cc4d13d 100644 --- a/isa_conflict_resolution.mdwn +++ b/isa_conflict_resolution.mdwn @@ -290,7 +290,7 @@ pressing issues to deal with that make resolving encoding conflicts trivial by comparison). Also pointed out was that in certain cases pipeline stalls could be introduced -during the switching phase, if needed. +during the switching phase, if needed. **This is the only one of the proposals that meet the full requirements** @@ -298,6 +298,28 @@ during the switching phase, if needed. TBD - [[ioctl]] for full details, summary kept here +This proposal basically mirrors the concept of POSIX ioctls, providing +(arbitrarily) 8 functions (opcodes) whose meaning may be over-ridden +in an object-orientated fashion by calling an "open handle" (and close) +function (instruction) that switches (redirects) the 8 functions over to +different opcodes. + +The proposal is functionally near-identical to that of the mvendor/march-id +except extended down to individual opcodes. As such it could hypothetically +be proposed as an independent Standard Extension in its own right that extends +the Custom Opcode space *or* fits into the brownfield spaces within the +existing ISA opcode space. + +One of the reasons for seeking an extension of the Custom opcode space is +that the Custom opcode space is severely limited: only 2 opcodes are free +within the 32-bit space, and only four total remain in the 48 and 64-bit +space. + +Despite the proposal (which is still undergoing clarification) +being worthwhile in its own right, and standing on its own merits and +thus definitely worthwhile pursuing, it is non-trivial and much more +invasive than the mvendor/march-id WARL concept. + # Discussion and analysis TBD