Re: [ECOS] Running code from on-chip flash

[Robin Randhawa <robin.randhawa@gmail.com>]

Hi.

On 30 Sep 2009, at 09:25, Mandeep Sandhu wrote:

> On Wed, Sep 30, 2009 at 1:20 PM, Bob Brusa <bob.brusa@gmail.com>  
> wrote:
>> Am 27.09.2009, 05:27 Uhr, schrieb Mandeep Sandhu
>> <mandeepsandhu.chd@gmail.com>:
>>
>>> Hi all,
>>>
>>> I'm going to be using a real hardware for the first time (with  
>>> ECOS).
>>> The h/w is the Atmel AT91SAM7X512 SoC.
>>>
>>> In order to save RAM, i'll be running the code from the on-chip  
>>> flash
>>> itself (512KB).
>>>
>>> Now is it true that if my code resides on the flash, I will not be
>>> able to write to it? I.e is the whole flash area is marked as
>>> readonly?
>>>
>>> Thanks,
>>> -mandeep
>>>
>> Yes, its true. You will not be able to run tricks like self- 
>> modifying code
>> that resides in flash. You would have to move such a routine to RAM  
>> and
>> execute it there.
>
> Ok, I'm confused now!
>
> Andrew mentioned that I _could_ write to a different area of the flash
> (i.e different from the one from where the code is running).
>
> To give an example, say I have to do a firmware upgrade. Now I
> download the image from, say an ethernet interface, and keep writing
> chunks of it (since the whole firmware image won't fit in my RAM of
> 128KB) to a "well-known" safe area on the flash.

IMHO, this is subject to the Flash part's abilities. I have worked  
with NOR Flash parts in the past where it was possible to run code  
from one sector while erasing/programming another sector. I suppose  
that the AT91SAM7X512's manuals and/or the Flash part manufacturer's  
manuals should shed light on this.

Bear in mind that the Flash chips might need a sector's worth of data  
to be buffered in RAM before writing to the sector in one go.

Cheers,
Robin

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