From: lkcl <lkcl@web>
Date: Fri, 16 Sep 2022 15:18:35 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~399
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=7a316cb8c159ba507a6278dea2f0b29d2d4a0fe3;p=libreriscv.git

---

diff --git a/openpower/sv/rfc/ls001.mdwn b/openpower/sv/rfc/ls001.mdwn
index d4cf3eb17..16bcb1630 100644
--- a/openpower/sv/rfc/ls001.mdwn
+++ b/openpower/sv/rfc/ls001.mdwn
@@ -911,6 +911,8 @@ must be allocated to a Vectoriseable EXT000-063
 "Defined Word" (Public v3.1 Section 1.6.3 definition)
 or not at all.
 
+\newpage{}
+
 **illegal unallocated scalar EXT0nn or EXT2nn:**
 
 | width | assembler | prefix?      | suffix    | description   |
@@ -932,6 +934,25 @@ there does not exist a scalar "Defined Word" (even for EXT200-263) - the
 unallocated block - means that the instruction may **not** be allocated in
 the Simple-V space.  
 
+**illegal attempt to put Scalar EXT004 into Vector EXT2nn**
+
+
+| width | assembler | prefix?      | suffix    | description   |
+|-------|-----------|--------------|-----------|---------------|
+| 32bit | unallocated | none         | 0x10345678| scalar EXT0nn |
+| 64bit | ss.fishmv | 0x24!zero    | 0x10345678| scalar SVP64Single:EXT2nn |
+| 64bit | sv.fishmv | 0x25nnnnnn   | 0x10345678| vector SVP64:EXT2nn |
+
+This is an illegal attempt to place an EXT004 "Defined Word"
+(Public v3.1 Section 1.6.3) into the EXT2nn Vector space.
+This is not just illegal it is not even possible to achieve.
+If attempted, by dropping EXT004 into bits 32-37, the top two
+MSBs are actually *zero*, and the Vector EXT2nn space is only
+legal for Primary Opcodes in the range 248-263, where the top
+two MSBs are 0b11.  Thus this faulty attempt actually falls
+unintentionally
+into `RESERVED` "Non-Vectoriseable" Encoding space.
+
 \newpage{}
 # Use cases