From: Luke Kenneth Casson Leighton Date: Mon, 30 Apr 2018 08:05:52 +0000 (+0100) Subject: add state information section X-Git-Tag: convert-csv-opcode-to-binary~5418 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=7819c23310828a45877bc8e1f6cfbb468dbe2435;p=libreriscv.git add state information section --- diff --git a/isa_conflict_resolution/mvendor_march_warl.mdwn b/isa_conflict_resolution/mvendor_march_warl.mdwn index 156f72ff0..0d75b2c0b 100644 --- a/isa_conflict_resolution/mvendor_march_warl.mdwn +++ b/isa_conflict_resolution/mvendor_march_warl.mdwn @@ -20,19 +20,24 @@ Beyond that, the change is so simple and straightforward that there is not much to discuss aside from its feasibility and its implications. The main considerations are: +* State information. How is state to be handled? * Compliance. What impact does the change have on Compliance (and testing)? * Implementation. Is it feasible and practical? * Exception-handlling. What happens during a trap? * Backwards compatibility. Is the change zero-impact (for existing systems) * Forwards compatibility. Does the change affect (limit) future hardware? -Note that unlike with MISA, state information is **not permitted to be -destroyed** during or by a switch-over. Switch-over to a different +## State information + +Unlike with MISA (which can be used to completely switch off - i.e. power +down) certain Extensions, state information is **not permitted to be +altered or destroyed** during or by a switch-over. Switch-over to a different mvendorid-marchid tuple shall have the effect of *purely* disabling certain instruction encodings and enabling others. -Note also that during context-switching *all* state of *all* custom -extensions (and variants of the Base Standards) are saved onto the stack, +Note also that during (for example) standard OS context-switching *all* +state of *all* extensions (and variants of the Base Standards) related +to *all* mvendorid-marchid tuples will need to be saved onto the stack, given that a hart may, at any time, switch between any available mvendorid-marchid tuples.