[Bug 1001606] Enable the cache on Kinetis in RAM startup mode

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--- Comment #35 from Jonathan Larmour <jifl@ecoscentric.com> 2012-11-03 06:42:59 GMT ---
Finally I reply....

First of all, to follow up a specific question you asked:

(In reply to comment #25)
> (In reply (addendum) to comment #23)
> 
> > Bus arbitration tweak for copy-back DDRAM 121008
> > 
> 
> Another consideration: It is possible to swap PC and PS priorities permanently
> for RAM startup. Then cache control macros will be shorter and there's no risk
> of preemption.. The drawback, if any, is that crossbar arbitration priorities
> for DDRAM will be different than the reset default. If implemented, this
> inversion could be fixed or configurable with CDL.
> Comments?

I don't have a very good feel for what the effects of this would be.
Specifically, can you imagine a situation when someone really would want the PC
priority to be higher than the PS one? I can't see it making a big difference
either way in the end, so I'm thinking a permanent change would be ok (although
if so, why wasn't it the reset default?).

As for the main patches.... I'm glad that the split cache scheme has made such
a great improvement in measured performance, as per our private email exchange.
It shows it was worth the effort!

One thing that strikes me as odd is the addition of CYG_HAL_STARTUP_DEF_ROM to
define CYG_HAL_STARTUP_ROM for RAM startup types. This seems potentially risky.
What problem was it intended to solve?

Other than that, I've reviewed everything already written in this issue, and
been through the current patches, and I don't see any reason not to commit the
patches. There might be a few essentially cosmetic things (spelling, typos,
etc.) that I could change, but minor touch-ups like that can be done after the
commit rather than going round the loop again.

Great work!

Jifl

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