From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 7 Oct 2019 15:03:48 +0000 (+0100)
Subject: add SHAPE CSR
X-Git-Tag: convert-csv-opcode-to-binary~3875
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=c63c527168b957ea86c809d5c9b994b6daa327d2;p=libreriscv.git

add SHAPE CSR
---

diff --git a/simple_v_extension/shape_table_format.mdwn b/simple_v_extension/shape_table_format.mdwn
new file mode 100644
index 000000000..46afddb95
--- /dev/null
+++ b/simple_v_extension/shape_table_format.mdwn
@@ -0,0 +1,37 @@
+Shape is 32-bits When SHAPE is set entirely to zeros, remapping is
+disabled: the register's elements are a linear (1D) vector.
+
+| 31..30   | 29..24 | 23..21  | 20..18  | 17..12  | 11..6   | 5..0    |
+| -------- | ------ | ------- | ------- | ------- | -------- | ------- |
+| applydim |modulo | invxyz | permute | zdimsz  | ydimsz  | xdimsz  |
+
+applydim will set to zero the dimensions less than this. applydim=0 applies all three. applydim=1 applies y and z. applydim=2 applys only z. applydim=3 is reserved.
+
+invxyz will invert the start index of each of x, y or z. If invxyz[0] is zero then x-dimensional counting begins from 0 and increments, otherwise it begins from xdimsz-1 and iterates down to zero. Likewise for y and z.
+
+modulo will cause the output to wrap and remain within the range 0 to modulo. The value zero disables modulus application. Note that modulo arithmetic is applied after all other remapping calculations.
+
+xdimsz, ydimsz and zdimsz are offset by 1, such that a value of 0 indicates
+that the array dimensionality for that dimension is 1.  A value of xdimsz=2
+would indicate that in the first dimension there are 3 elements in the
+array.  The format of the array is therefore as follows:
+
+    array[xdim+1][ydim+1][zdim+1]
+
+However whilst illustrative of the dimensionality, that does not take the
+"permute" setting into account.  "permute" may be any one of six values
+(0-5, with values of 6 and 7 being reserved, and not legal).  The table
+below shows how the permutation dimensionality order works:
+
+| permute | order | array format             |
+| ------- | ----- | ------------------------ |
+| 000     | 0,1,2 | (xdim+1)(ydim+1)(zdim+1) |
+| 001     | 0,2,1 | (xdim+1)(zdim+1)(ydim+1) |
+| 010     | 1,0,2 | (ydim+1)(xdim+1)(zdim+1) |
+| 011     | 1,2,0 | (ydim+1)(zdim+1)(xdim+1) |
+| 100     | 2,0,1 | (zdim+1)(xdim+1)(ydim+1) |
+| 101     | 2,1,0 | (zdim+1)(ydim+1)(xdim+1) |
+
+In other words, the "permute" option changes the order in which
+nested for-loops over the array would be done.
+
diff --git a/simple_v_extension/vblock_format.mdwn b/simple_v_extension/vblock_format.mdwn
index 4bb17f5cb..680d747bd 100644
--- a/simple_v_extension/vblock_format.mdwn
+++ b/simple_v_extension/vblock_format.mdwn
@@ -159,6 +159,9 @@ The shape table format is included here for convenience:
 
 [[!inline raw="yes" pages="simple_v_extension/shape_table_format" ]]
 
+See [[simple_v_extension/remap]] for full details on how SHAPE applies,
+including pseudo-code.
+
 REMAP Shape blocks are only accessible using the "VBLOCK2" format.
 
 # CSRs: