From: Luke Kenneth Casson Leighton Date: Wed, 10 Oct 2018 05:21:10 +0000 (+0100) Subject: add recommendation on unused elements X-Git-Tag: convert-csv-opcode-to-binary~4966 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=f1c9644fe02732fbdcd73e49ba29c98774c45ec9;p=libreriscv.git add recommendation on unused elements --- diff --git a/simple_v_extension/specification.mdwn b/simple_v_extension/specification.mdwn index e27a446c6..5e0c1b311 100644 --- a/simple_v_extension/specification.mdwn +++ b/simple_v_extension/specification.mdwn @@ -804,4 +804,13 @@ No specific hints are yet defined in Simple-V # Under consideration -placeholder +for element-grouping, if there is unused space within a register +(3 16-bit elements in a 64-bit register for example), recommend: + +* For the unused elements in an integer register, the used element + closest to the MSB is sign-extended on write and the unused elements + are ignored on read. +* The unused elements in a floating-point register are treated as-if + they are set to all ones on write and are ignored on read, matching the + existing standard for storing smaller FP values in larger registers. +