[ECOS] Is cache disabling necessary during flash programming/erase cycles?

[Gary Thomas]

Lars Povlsen wrote:
> Gary Thomas wrote:
>>
>> Lars Povlsen wrote:
>> > Hello folks,
>> > > Many of the flash_XXX() functions in
>> > .../packages/io/flash/current/src/flash.c have the caches disabled 
>> while
>> > accessing the flash.
>> >
>> > According to flash.h - and I quote -
>> >
>> > "Execution of flash code must be done inside a
>> > HAL_FLASH_CACHES_OFF/HAL_FLASH_CACHES_ON region - disabling the 
>> cache on
>> > unified cache systems is necessary to prevent burst access to the flash
>> > area being programmed. With Harvard style caches, only the data cache
>> > needs to be disabled, but the instruction cache is disabled for
>> > consistency".
>> > > In our case we have a Harvard style cache running on an ARM9. The
>> > address space covered by the flash is uncached and unbuffered (We're
>> > running ROMRAM), so my question is:
>> >
>> > Is disabling of the DCache really needed on such a system?
>>
>> Probably not, but not doing so will probably not affect the
>> performance greatly since you'll still be stuck in those loops
>> waiting for the device to do its thing.
>>
> Gary,
> 
> Problem is not so much the flash performance - its the *rest* of the 
> system while the flash is being updated (config update in this case). 
> The system becomes very sluggish during the update.
> 
> We'll probably do a CDL option to disable the disable (:-) Is a patch of 
> interest if it pans out OK?

Sure, please send it on.

Note: I think that much of this effort is already present in the
FLASHv2 branch (but I've not used it, so I can't say for sure)

> 
> PS: The flash accesses (read as well as write) are guarded by a  mutex  
> at system level.


-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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