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diff --git a/openpower/sv.mdwn b/openpower/sv.mdwn
index a669890a3c01f3a6e39ac30309869090f760c840..b596be280402662a502ddd7bb622d0bf876d40b5 100644 (file)
--- a/openpower/sv.mdwn
+++ b/openpower/sv.mdwn
@@ -221,10 +221,11 @@ submit RFCs once the External ISA WG RFC Process is in place and,
 in a wholly unsatisfactory manner have to *hope and trust* that
 OPF ISA WG Members are reading this and take it into consideration.
 
+**Scalar Summary**
+
 As above sections, it is emphasised strongly that Simple-V in no
 way critically depends on the 100 or so *Scalar* instructions also
-being developed by Libre-SOC. Therefore the Opcode summary below is
-again divided into two: SVP64, then Scalar instructions.
+being developed by Libre-SOC.
 
 **None of these Draft opcodes are intended for private custom
 secret proprietary usage. They are all intended for entirely
@@ -237,10 +238,18 @@ same level as add, popcnt and fld**
   requires multiple VA-Form operations (in greater numbers
   than EXT04 has spare)
 * space in EXT019 next to addpcis and crops is recommended
-  (or any 5-6 bit Minor XO areas)
+  (or any other 5-6 bit Minor XO areas)
 * many X-Form opcodes currently in EXT022 have no preference
   for a location at all, and may be moved to EXT059, EXT019,
   EXT031 or other much more suitable location.
+* even if ratified and even if the majority (X-Form)
+  is moved to other locations the large immediate sizes of 
+  the remaining bitmanip instructions means
+  it would be highly likely they would need two
+  major opcodes.  Fortunately EXT005 and EXT009 are
+  available.
+
+**Additional observations**
 
 Note that there is no Sandbox allocation in the published ISA Spec for
 v3.1 EXT01 usage, and because SVP64 is already 64-bit Prefixed,
@@ -249,6 +258,14 @@ would become a whopping 96-bit long instruction. Avoiding this
 situation is a high priority which in turn by necessity puts pressure
 on the 32-bit Major Opcode space.
 
+SVP64 itself is already under pressure, being only 24 bits.  If it is
+not permitted to take up 25% of EXT001 then it would have to be proposed
+in its own Major Opcode, which on first consideration would be beneficial
+for SVP64. However when combined with the bitmanip scalar instructions
+requiring two Major opcodes this would come to a grand total of 3 precious
+Major opcodes. On balance, then, sacrificing 25% of EXT001 is the "least
+difficult" choice.
+
 Note also that EXT022, the Official Architectural Sandbox area
 is under severe design pressure as it is insufficient to hold
 the full extent of the instruction additions required to create