From: lkcl <lkcl@web>
Date: Wed, 14 Sep 2022 18:25:19 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~443
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=5c450a7a4b6e49fa7715ffcbe6396b033c60734f;p=libreriscv.git

---

diff --git a/openpower/sv/rfc/ls001.mdwn b/openpower/sv/rfc/ls001.mdwn
index 8bc64c28f..296c8382d 100644
--- a/openpower/sv/rfc/ls001.mdwn
+++ b/openpower/sv/rfc/ls001.mdwn
@@ -181,11 +181,17 @@ the same space):
   (fits within svshape's XO encoding)
 * **svindex** - convenience instruction for setting up "Indexed" REMAP.
 
-# SVP64 and SVP64-Single 24-bit Prefixes
+# SVP64 24-bit Prefixes
+
+The SVP64 24-bit Prefix (RM) provides several options,
+all fitting within the 24-bit space (and no other).
+These Modes do not interact with SVSTATE per se.  SVSTATE
+primarily controls the looping (quantity, order), RM
+influences the *elements* (the Suffix).  There is however
+some close interaction when it comes to predication.
+REMAP is separately
+outlined in another section.
 
-The SVP64 24-bit Prefix provides several options,
-all fitting within the 24-bit space (and no other). REMAP is separately
-outlined below.
 The primary options all of which are aimed at reducing instruction
 count and reducing assembler complexity are:
 
@@ -197,7 +203,12 @@ count and reducing assembler complexity are:
   between all formats.
 * predication.  this is an absolutely essential feature for a 3D GPU VPU ISA.
   CR Fields are available as Predicate Masks hence the reason for their
-  extension to 128.
+  extension to 128. Twin-Predication is also provided: this may best
+  be envisaged as back-to-back VGATHER-VSCATTER but is not restricted
+  to LD/ST, its use saves on instruction count.  Enabling one or other
+  of the predicates provides all of the other types of operations
+  found in Vector ISAs (VEXTRACT, VINSERT etc) again with no need
+  to actually provide explicit such instructions.
 * Saturation. **all** LD/ST and Arithmetic and Logical operations may
   be saturated (without adding explicit scalar saturated opcodes)
 * Reduction and Prefix-Sum (Fibonnacci Series) Modes