note about naming

diff --git a/openpower/sv/svp_rewrite/svp64.mdwn b/openpower/sv/svp_rewrite/svp64.mdwn
index b3048cce6b8f3a40beea52c1329e81b771e5ffeb..60f834077cd704038c50eb4c5f6d36100082e8d0 100644 (file)
--- a/openpower/sv/svp_rewrite/svp64.mdwn
+++ b/openpower/sv/svp_rewrite/svp64.mdwn
@@ -402,6 +402,12 @@ of the OpenPOWER v3.0B / v3.1B register naming, and in hardware this
 would be reflected by a linear increase in the size of the underlying
 SRAM used for the regfiles.
 
+Note: when the EXTRA fields are all zero, SV is deliberately designed
+so that the register fields are identical to as if SV was not in effect
+i.e. under these circumstances (EXTRA=0) the register field names RA,
+RB etc. are interpreted as v3.0B / v3.1B scalar registers.  This is termed
+`scalar identity behaviour`
+
 # Operation
 
 ## CR fields as inputs/outputs of vector operations