MLBEDSW-7871: Document new error types in API

- Documents Legality requirements of CMD1 payloads

- Fixes a miss in the command stream checks.

Signed-off-by: William Isaksson <william.isaksson@arm.com>
Change-Id: I9b33dedfa66650fa3100f61fd158a385818b4d52
diff --git a/ethosu/vela/register_command_stream_generator.py b/ethosu/vela/register_command_stream_generator.py
index 42ae99d..9d9a1e6 100644
--- a/ethosu/vela/register_command_stream_generator.py
+++ b/ethosu/vela/register_command_stream_generator.py
@@ -531,6 +531,7 @@
             emit.cmd1_with_offset(length, weights[core].length)
         elif core < arch.ncores:
             check_alignment(weights[0].address, 16)
+            check_length(weights[0].length, 16)
             emit.cmd1_with_address(addr, weights[0].address)
             emit.cmd1_with_offset(length, 0)