From: Luke Kenneth Casson Leighton Date: Thu, 20 Feb 2020 11:47:21 +0000 (+0000) Subject: add para about example namespaces that already exist X-Git-Tag: convert-csv-opcode-to-binary~3336 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=74eb5f7c6f9cdfa215373a01930d84e5e1eefd66;p=libreriscv.git add para about example namespaces that already exist --- diff --git a/isa_conflict_resolution/isamux_isans.mdwn b/isa_conflict_resolution/isamux_isans.mdwn index 5bd4a122a..d0f85e509 100644 --- a/isa_conflict_resolution/isamux_isans.mdwn +++ b/isa_conflict_resolution/isamux_isans.mdwn @@ -17,6 +17,16 @@ be relevant for a fixed number of instructions at a time. Caveat: allowing such a countdown to cross branch-points is unwise (illegal instruction?) +An example of a pre-existing "namespace" switch that has been in +prevalent use for several decades (SPARC and other architectures): +dynamic runtime selectability of littel-endian / big-endian "meaning" +of instructions by way of a "mode switch" instruction (of some kind). + +That "switch" is in effect a 33rd (hidden) bit that is part of the opcode, +going directly into the mux / decode phase of instruction decode, and +thus qualifies categorically as a "namespace". This proposal both formalises +and generalises that concept. + # Hypothetical Format Note that this is a hypothetical format, yet TBD, where particular attention