From f0a3ec4fb382c096138f4ca3e9cc68c8285fab88 Mon Sep 17 00:00:00 2001 From: lkcl Date: Sun, 4 Jul 2021 18:40:44 +0100 Subject: [PATCH] --- openpower/sv/register_type_tags.mdwn | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/openpower/sv/register_type_tags.mdwn b/openpower/sv/register_type_tags.mdwn index 7c77cdee2..4b7587a32 100644 --- a/openpower/sv/register_type_tags.mdwn +++ b/openpower/sv/register_type_tags.mdwn @@ -8,6 +8,13 @@ A concept present in processors such as Texas Instruments DSPs and in the Mill A This for allows instructions originally designed to only be IEEE754 FP64 fir example to become IEEE754 FP128 or even complex mumbers. With SVP64 supporting [[sv/remap]] it is not conceptually that much of a leap to support complex numbers, given that the hardware to do so is already in place. +It is however extremely important to keep the tag context down to a bare minimum size, because, like SVSTATE, it has to be added to the interrupt context alongside SRR0 and SRR1. + +Interestingly due to the size of complex numbers (and FP128) there is not much point having large tags. It is quite likely therefore that a 64 bit SPR of 2 bits per register, covering 128 registers, would be sufficient. Groups of 4 registers would be tagged: + +* SVTAG[0:1] marks all of FPR[0..3] and GPR[0..3] + + Links: * -- 2.30.2