From: lkcl <lkcl@web>
Date: Mon, 11 Oct 2021 18:19:06 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~3647
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=2a2d77a7cc06c8f44c8b81aff683d0e9c42807e4;p=libreriscv.git

---

diff --git a/3d_gpu/architecture/dynamic_simd/shape.mdwn b/3d_gpu/architecture/dynamic_simd/shape.mdwn
index d9c83df73..94b4cbc7e 100644
--- a/3d_gpu/architecture/dynamic_simd/shape.mdwn
+++ b/3d_gpu/architecture/dynamic_simd/shape.mdwn
@@ -5,6 +5,8 @@ Links:
 * [layout experiment](https://git.libre-soc.org/?p=ieee754fpu.git;a=blob;f=src/ieee754/part/layout_experiment.py;h=2a31a57dbcb4cb075ec14b4799e521fca6aa509b;hb=0407d90ccaf7e0e42f40918c3fa5dc1d89cf0155)
 * <https://bugs.libre-soc.org/show_bug.cgi?id=713>
 
+# Requirements Analysis
+
 A logical extension of the nmigen `ast.Shape` concept, `SimdShape`
 provides sufficient context to both define overrides for individual lengths
 on a per-mask basis as well as sufficient information to "upcast"
@@ -199,5 +201,19 @@ Thus not one method of setting widths is required but *two*:
 * at the element level
 * at the width of the entire SIMD signal
 
+With this background and context in mind the requirements can be determined
+
 # Requirements
 
+SimdShape needs:
+
+* to derive from nmigen ast.Shape in order to provide the overall
+  width and whether it is signed or unsigned.  However the
+  overall width is not necessarily hard-set but may be calculated
+* to support a range of sub-signal divisions (element widths)
+  and for there to be an option to either set each element width
+  explicitly or to allow each width to be computed from the
+  overall width and the number of partitions.
+* to provide rudimentary arithmetic operator capability
+  that automatically computes a new SimdShape, adjusting width
+  and element widths accordingly.