[Libre-soc-dev] LD/ST Elwidth Overrides

lkcl luke.leighton at gmail.com
Wed Sep 1 15:52:05 BST 2021

discussion today about elwidth overrides, applying to LD/ST, on IRC:


i realised, there is a triangle of elwidth match and mismatches, because there are *THREE* widths involved.  let's take LDs:

* operation width ld=64 lw=32 lh=16 lb=8
* src elwidth override applies to memory, dflt/32/16/8
* dest elwidth override applies to the register
   receiving the data being read.

when the src elwidth is greater *or equal* to the operation width, everything is logical and fine.

when the src elwidth is LESS than the operation width, this is effectively asking for overlapping memory READ operations, and is not fine.

for STs which would involve overlapping memory WRITE operations it's definitely not fine.

question: what should the behaviour be?


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