From: lkcl Date: Mon, 30 Nov 2020 16:32:46 +0000 (+0000) Subject: (no commit message) X-Git-Tag: convert-csv-opcode-to-binary~1599 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=11ad3ec18b1026e81cfda522fa5ac38d5b423879;p=libreriscv.git --- diff --git a/openpower/sv/16_bit_compressed.mdwn b/openpower/sv/16_bit_compressed.mdwn index ffee17c93..b4422ac7e 100644 --- a/openpower/sv/16_bit_compressed.mdwn +++ b/openpower/sv/16_bit_compressed.mdwn @@ -102,13 +102,14 @@ VLE was a means to reduce executable size through three interleaved methods: * (1) invention of 16 bit encodings (of exactly 16 bit in length) * (2) invention of 16+16 bit encodings (a 16 bit instruction format but with - an *additional* 16 bit immediate "tacked on" to the end) + an *additional* 16 bit immediate "tacked on" to the end, actually + making a 32-bit instruction format) * (3) seamless and transparent embedding and intermingling of the above in amongst arbitrary v2.06/7 BE 32 bit instruction sequences, with no additional state, including when the PC was not aligned on a 4-byte boundary. -Whilst (1) and (3) make perfect sense, (2) makes no sense at all given that 16 bit immediates is the norm for v2.06/7 and v3.0B standard instructions. (2) in effect **is** a 32 bit instruction. (2) **is not** a 16 bit instuction. Why "reinvent" an encoding that is 32 bit, when there already exists a 32 bit encoding that does the exact same job? +Whilst (1) and (3) make perfect sense, (2) makes no sense at all given that, inspection of "ori" and others, I-Form 16 bit immediates is the "norm" for v2.06/7 and v3.0B standard instructions. (2) in effect **is** a 32 bit instruction. (2) **is not** a 16 bit instuction. Why "reinvent" an encoding that is 32 bit, when there already exists a 32 bit encoding that does the exact same job? Consequently, we do **not** envisage a scenario where (2) would ever be implemented, nor in the future would this Compressed Encoding be extended beyond 16 bit. Compressed is Compressed and is **by definition** limited to precisely - and only - 16 bit.