SPI/Cache :: Line-Wrap mode vs. Line-base-first mode. Which one to choose?

Document created by analog-archivist Employee on Feb 23, 2016
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SPI/Cache :: Line-Wrap mode vs. Line-base-first mode. Which one to choose?

 

Wrap mode
Wrap mode is a specific feature supported by most flash devices in market. It
enables the host processor to ask for the critical word first in a cache line.
If enabled, the core is delivered with the critical word it asked for, as soon
as possible (for instance, branching address). When using this mode, the Cache
Controller, SPI Controller and the Flash device, all three blocks must be
pre-programmed to support the same.
Line-Wrap mode vs. Line-base-first mode
In Line-base-first mode, the line is always fetched starting at offset 0 (line
base) while in line-wrap mode, the critical word is returned first; the rest of
the line is fetched with wrap-around addressing. In Line-wrap mode, merging is
not possible (not linear). Usually, line-base-first will be faster due to
merging.
How to decide
Decision is application dependent. User has to experiment with his software,
before deciding up on the mode. Some applications require that critical
instruction be executed very fast, so in such cases Wrap mode maybe used. For
typical cases where one wants better linear throughput, Line base first mode
maybe a better choice.

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