(no commit message)

diff --git a/openpower/sv/branches.mdwn b/openpower/sv/branches.mdwn
index 1fcafc83f798acbdc837351a7010f2ac8bca8649..a467de30d8691a0bd05a88449e2e462107d233c9 100644 (file)
--- a/openpower/sv/branches.mdwn
+++ b/openpower/sv/branches.mdwn
@@ -99,9 +99,9 @@ SVP64 RM `MODE` (includes `ELWIDTH` and `ELWIDTH_SRC` bits) for Branch Condition
 | 4 | 5 | 6 | 7 | 19 | 20 |  21 | 22   23 |  description        |
 | - | - | - | - | -- | -- | --- |---------|-------------------- |
 |ALL|LRu| / | / | 0  | 0  | /   |  SNZ sz | normal mode         |
-|ALL|LRu| / | / | 0  | 1  | VLI |  SNZ sz | VLSET mode          |
+|ALL|LRu| / |VSb| 0  | 1  | VLI |  SNZ sz | VLSET mode          |
 |ALL|LRu|BRc| / | 1  | 0  | /   |  SNZ sz | svstep mode         |
-|ALL|LRu|BRc| / | 1  | 1  | VLI |  SNZ sz | svstep+VLSET mode   |
+|ALL|LRu|BRc|VSb| 1  | 1  | VLI |  SNZ sz | svstep+VLSET mode   |
 
 Fields:
 
@@ -113,7 +113,8 @@ Fields:
 * **VLI** Identical to Data-dependent Fail-First mode.
   In VLSET mode, VL is set equal (truncated) to the first point
   where, assuming Conditions are tested sequentially, the  branch succeeds
-  *or fails*.  If VLI (Vector Length Inclusive) is clear,
+  *or fails* depending if VSb is set.
+  If VLI (Vector Length Inclusive) is clear,
   VL is truncated to *exclude* the current element, otherwise it is
   included. SVSTATE.MVL is not changed: only VL.
 * **LRu**: Link Register Update. When set, Link Register will
@@ -121,6 +122,9 @@ Fields:
   destruction of LR during loops.
 * **BRc** Branch variant of Rc. Instructs svstep testing to overwrite
   the CR Field about to be tested
+* **VSb** is most relevant for Vertical-First VLSET Mode. After testing,
+  if VSb is set, VL is truncated if the branch succeeds.  If VSb is clear,
+  VL is truncated if the branch did **not** take place.
 
 svstep mode will run an increment of SVSTATE srcstep and dststep
 (which is still useful in Horizontal First Mode).  Unlike `svstep.`
@@ -136,8 +140,13 @@ and `svstep` mode it is actually useful to use Branch Conditional even
 to perform no actual branch operation, i.e to point to the instruction
 after the branch.
 
-`VLSET` mode with Vertical-First is particularly unusual. TODO
-investigate svstep index checks.
+`VLSET` mode with Vertical-First is particularly unusual. Vertical-First
+is used for explicit looping, where the looping is to terminate if
+the end of the Vector, VL, is reached. If however that loop is terminated
+early because VL is truncated, VLSET with Vertical-First becomes
+meaningless.  Therefore, the option to decide whether truncation should
+occur if the branch succeeds *or* if the branch condition fails allows
+for flexibility required.
 
 In particular, svstep mode is still useful for Horizontal-First Mode
 particularly in combination with REMAP. All "loop end" conditions