From: lkcl <lkcl@web>
Date: Mon, 21 Dec 2020 05:09:27 +0000 (+0000)
Subject: (no commit message)
X-Git-Tag: convert-csv-opcode-to-binary~1094
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=d217cf41151f6d3f2dbed1e5d93974db01aab9fb;p=libreriscv.git

---

diff --git a/openpower/sv/svp_rewrite/svp64.mdwn b/openpower/sv/svp_rewrite/svp64.mdwn
index 924231da7..5e5edd900 100644
--- a/openpower/sv/svp_rewrite/svp64.mdwn
+++ b/openpower/sv/svp_rewrite/svp64.mdwn
@@ -32,6 +32,17 @@ v3.0/1B instructions covered by the prefix are "unaltered". This is termed `scal
 Note that this is completely different from when VL=0.  VL=0 turns all operations under its influence into `nops` (regardless of the prefix)
  whereas when VL=1 and the SV prefix is all zeros, the operation simply acts as if SV had not been applied at all to the instruction  (an "identity operation").
 
+# XER, SO and other global flags
+
+Vector systems are expected to be high performance.  This is achieved
+through parallelism, which requires that elements in the vector be
+independent.  XER SO and other global "accumulation" flags (CR.OV) cause
+Read-Write Hazards on single-bit global resources, having a significant
+detrimental adverse effect.
+
+Consequently in SV, XER.SO and CR.OV behaviour is disregarded.  XER is
+simply neither read nor written.  
+
 # Register Naming
 
 SV Registers are simply the INT, FP and CR register files extended