MTD with non-power-of-2 page size

[Simon Aittamaa]

On 12 August 2015 at 13:21, Dave Kitchen <dave.kitchen at insync.tv> wrote:
>
> I have just started to work with barebox on an Atmel at91sam9g45 processor.
> The board has an Atmel AT45DB161 dataflash configured as 528-byte page size.
> I find that eg saveenv command does not run as the page erase fails with
> EINVAL. On tracing this is fired from the page size and offset correction
> code [mtd/core,c mtd_erase_align()] which uses bit masking to align the size
> and offset. Unfortunately bit-masking does not work with non-power-of-2
> pages. Has anyone else addressed this problem?
>

Yes, it's a bit of an annoying problem...

The easy solution (if you can spare the space) is to increase the
partition size, e.g. 128*528 should work (which is what I'm currently
using) and any multiple thereof. I'm fairly certain that 64*528 (and
any multiple thereof) should also work, but it was a while since I
messed around with that so you'll have to test it yourself.

You can also reprogram the device to present pages that are
power-of-two, but you should be aware that you lose some space
(pages*16) and the process is not reversible (you've been warned!),
see the datasheet for more information.

Best,
Simon Aittamaa

> The 'trivial' exercise of replacing the bit masks by modulo [%] operator
> does not succeed as the compiler I am using (gcc!) does not support
> long-long divmod.
>
> Regards
> Dave Kitchen
> InSync technology Ltd
>
>
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