From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 5 Apr 2023 09:57:38 +0000 (+0100)
Subject: programmers note about RC1 with DD-FF-LDST
X-Git-Tag: opf_rfc_ls012_v1~122
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=52ede886a947132e4f4218f1fb6dc143c31cc44a;p=libreriscv.git

programmers note about RC1 with DD-FF-LDST
---

diff --git a/openpower/sv/ldst.mdwn b/openpower/sv/ldst.mdwn
index 1623f513f..614dc6ed0 100644
--- a/openpower/sv/ldst.mdwn
+++ b/openpower/sv/ldst.mdwn
@@ -477,6 +477,10 @@ nodes.  If VLi=1 it will load the NULL pointer into the Vector of results.
 If however VLi=0 it will *exclude* the NULL pointer by truncating VL to
 one Element earlier.
 
+*Programmer's Note: by also setting the RC1 qualifier as well as setting
+VLi=1 it is possible to establish a Predicate Mask such that the first
+zero in the predicate will be the NULL pointer*
+
 ```
    RT=1 # vec - deliberately overlaps by one with RA
    RA=0 # vec - first one is valid, contains ptr