From: lkcl <lkcl@web>
Date: Fri, 2 Sep 2022 22:47:13 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~722
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ef90a7ad113d1a68626e3ec2124b4b709becd61b;p=libreriscv.git

---

diff --git a/openpower/sv/remap.mdwn b/openpower/sv/remap.mdwn
index 26f5b945f..e6aea5fc5 100644
--- a/openpower/sv/remap.mdwn
+++ b/openpower/sv/remap.mdwn
@@ -636,7 +636,18 @@ the SVSTATE SPRs manually.
 # svshape2 (offset) <a name="svshape2"> </a>
 
 `svshape2` is an additional convenience instruction that prioritises
-setting `SVSHAPE.offset`. It has similar cap
+setting `SVSHAPE.offset`. It has identical capabilities to `svindex` and
+in terms of both options (skip, etc.) and ability to activate REMAP
+(rmm, mask mode) but unlike `svindex` it does not set GPR REMAP,
+only a 1D or 2D `svshape`, and
+unlike `svshape` it can set an arbirrary `SVSHAPE.offset` immediate.
+
+One of the limitations of Simple-V is that Vector elements start on the boundary
+of the Scalar regfile, which is fine when element-width overrides are not
+needed. If the starting point of a Vector with smaller elwidths must begin
+in the middle of a register, normally there would be no way to do so except
+through LD/ST.  `SVSHAPE.offset` caters for this scenario and `svshape2`is
+makes it easier.
 
     svshape2 offs,inv,yx,rmm,SVd,sk,mm