From: lkcl <lkcl@web>
Date: Sun, 26 Mar 2023 11:36:24 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls001_v3~58
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4794155abcf2b79b98afff684ed856c020f2a60d;p=libreriscv.git

---

diff --git a/openpower/sv/rfc/ls008.mdwn b/openpower/sv/rfc/ls008.mdwn
index 9ce790e97..b0c93da8b 100644
--- a/openpower/sv/rfc/ls008.mdwn
+++ b/openpower/sv/rfc/ls008.mdwn
@@ -81,6 +81,7 @@ TODO
 
 Add the following entries to:
 
+* Section 1.3.2 Notation
 * the Appendices of Book I
 * Instructions of Book I as a new Section
 * SVL-Form of Book I Section 1.6.1.6 and 1.6.2
@@ -89,6 +90,20 @@ Add the following entries to:
 
 \newpage{}
 
+# Notation, Section 1.3.2
+
+When register operands (RA, RT, BF) are prefixed by a single underscore
+(_RT, _RA, _BF) the variable contains the contents of the instruction field
+not the contents of the Register File referenced *by* that field. Example:
+`_RT` contains the contents of bits 5 thru 10. The relationship
+`RT = GPR(_RT)` is thus always true. Uses include making alternative
+decisions within an instruction based on whether the operand field
+is zero or non-zero.
+
+----------------
+
+\newpage{}
+
 # svstep: Vertical-First Stepping and status reporting
 
 SVL-Form
@@ -162,10 +177,10 @@ Pseudo-code:
     SVSTATE[7:13] <- VL
     if _RT != 0 then
        GPR(_RT) <- [0]*57 || VL
-    if ((¬vs) & ¬(ms)) = 0 then
-        # set requested Vertical-First mode, clear persist
-        SVSTATE[63] <- vf
-        SVSTATE[62] <- 0b0
+    # MAXVL is a static "state-reset" opportunity so VF is only set then.
+    if ms = 1 then
+         SVSTATE[63] <- vf   # set Vertical-First mode
+         SVSTATE[62] <- 0b0  # clear persist bit
 ```
 
 Special Registers Altered:
@@ -413,11 +428,12 @@ Add the following to Book I, 1.6.2
         Field used in Simple-V to specify whether VL (vl in the SVSTATE SPR) is to be set
         Formats: SVL
     SVi (16:22)
-         Simple-V immediate field for setting VL or MVL (vl, maxvl in the SVSTATE SPR)
+         Simple-V immediate field used by setvl for setting VL or MVL
+         (vl, maxvl in the SVSTATE SPR)
+         and used as a "Mode of Operation" selector in svstep
          Formats: SVL
 ```
 
-
 # Appendices
 
     Appendix E Power ISA sorted by opcode
@@ -428,4 +444,5 @@ Add the following to Book I, 1.6.2
 | Form | Book | Page | Version | mnemonic | Description |
 |------|------|------|---------|----------|-------------|
 | SVL  | I    | #    | 3.0B    | svstep   | Vertical-First Stepping and status reporting |
+| SVL  | I    | #    | 3.0B    | setvl    | Cray-like establishment of Looping (Vector) context |