[ECOS] cyg_flash_program_mask

[Andrew Dyer]

On Tue, Feb 15, 2011 at 10:07, Tom Schouten <tom@zwizwa.be> wrote:
> Hi folks,
>
> It seems that many Flash devices expose separate "program" and "erase"
> operations.  It also seems fairly common to represent an erased bit as
> "1" and a programmed bit as "0".  In this view "program" can only
> perform a 1->0 transition and "erase" resets bits back to 1.  So a
> Flash chip's "program" operation is logically an "and-mask" operation.
>
> Since the erase operation is one that ages the chip, it makes sense in
> some applications to use multiple overlaying "and-mask" operations to
> incrementally write to data units that are smaller than the smallest
> erase unit.
>
> Is there any interest to add support for this behaviour to the eCos
> API?
>
> If I understand correctly, the cyg_flash_program() operation erases
> before program such that the resulting bit pattern in the Flash always
> represents the input bit pattern exactly, instead of being the result
> of an "and-mask" operation.
>
> A single extra API function could be enough:
>
> int cyg_flash_program_mask(cyg_flashaddr_t flash_base,
>                           void *ram_base, size_t len,
>                           cyg_flashaddr_t *err_address);
>

You have to be very careful doing this.  At least some NAND flash
parts have restrictions on how many 'partial page program' cycles you
can do.  For the part I am using, the restriction is 4 for normal
memory pages, and 8 for the one time programmable area.

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