sync_up: Discussion page for tomorrow's meeting

[libreriscv.git] / simple_v_extension / vblock_format.mdwn

diff --git a/simple_v_extension/vblock_format.mdwn b/simple_v_extension/vblock_format.mdwn
index 4bb17f5cb7e7a2775cd487cdc756c04820eb0095..c851ee17227fa0011f0529a7be555de6b11a9fd2 100644 (file)
--- a/simple_v_extension/vblock_format.mdwn
+++ b/simple_v_extension/vblock_format.mdwn
@@ -1,4 +1,4 @@
-[[!tag standards]]
+[[!tag oldstandards]]
 
 # Simple-V (Parallelism Extension Proposal) Vector Block Format
 
@@ -153,9 +153,41 @@ The swizzle table format is included here for convenience:
 
 Swizzle blocks are only accessible using the "VBLOCK2" format.
 
+The swizzles activate on SUBVL and only when used in an operation where a register matches with a SwizzleCAM register entry.
+
+On a match the register element index will be redirected through the swizzle format. If however the type is set to "constants" then instead of reading the register file the relevant constant is substituted instead.
+
+Setting const type on a destination element will cause an illegal instruction.
+
+
+# REMAP Area Format<a name="remap_format"></a>
+
+REMAP is an algorithmic version of in-place vector "vgather" or "swizzle".
+
+The REMAP area is divided into two areas:
+
+* Register-to-SHAPE.  This defines which registers have which shapes.
+  Each entry is 8-bits in length.
+* SHAPE Table entries.  These are 32-bits in length and are aligned
+  to (start on) a 16 bit boundary.
+
+REMAP Table Entries:
+
+| 7:5      | 4:0    |
+| -------- | ------ |
+| shapeidx | regnum |
+
+When both shapeidx and regnum are zero, this indicates the end of the
+REMAP Register-to-SHAPE section.  The REMAP Table section size is then
+aligned to a 16-bit boundary.  32-bit SHAPE Table Entries then fill the
+remainder of the REMAP area, and are indexed in order by shapeidx.
+
+In this way, multiple registers may share the same "shape" characteristics.
+
 # SHAPE Table Format<a name="shape_format"></a>
 
-The shape table format is included here for convenience:
+The shape table format is included here for convenience. See [[simple_v_extension/remap]] for full details on how SHAPE applies,
+including pseudo-code.
 
 [[!inline raw="yes" pages="simple_v_extension/shape_table_format" ]]