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

lkcl luke.leighton at gmail.com
Thu Sep 2 20:48:02 BST 2021

On September 2, 2021 7:37:29 PM UTC, Hendrik Boom <hendrik at topoi.pooq.com> wrote:

(thanks for rhe insightful questions, hendrik, do please remember to trim context)

>> this is not Data-Dependent FFIRST, it is LDST FFIRST, and the
>behaviour is subtly different.
>So the subtle difference here arises because with Data-Dependent the
>are already available, such as in registers or available when pevious 
>calculations complete, but LDST has to fetch from storage, which could 
>incur arbitrary delays and page faults?

that is actually part of it, i hadn't thought of it that way, that DD-FF is on arithmetic data but LDST-FF is on the action of *memory accessing*.

* an individual LDST-FF element load could fail (throw exception)
* an individual DD-FF element test cannot "fail" (throw exception)

therefore, with no exception being possible, DD-FF can be explicit and strictly defined.  more to the point, arbitrary truncation is meaningless on DD-FF.


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