Re: [ECOS] Supporting Paged Flash in eCos/RedBoot

["Gary D. Thomas" <gary dot thomas at mind dot be>]

On Mon, 2003-02-17 at 10:36, Ian Campbell wrote:
> Hi,
> 
> I am porting eCos (RedBoot in particular) to a target board which uses
> pages flash. That is, the flash appears as a 16k window at 0xD0000 which
> you can point to different offsets in the physical flash device[0]. 
> 
> My aim is to properly support the full flash on this target (and
> probably several more in the future), especially RedBoot fis and flash
> config support, and I would like to do it in a way which the eCos
> maintainers would be happy accepting a patch back into eCos -- since it
> is likely to touch a fair amount of code in the flash driver and redboot
> etc and I don't really want to maintain a huge out of tree patch if I
> can avoid it.
> 
> Currently all flash access is done by directly reading and writing
> though pointers into the flash region and by using memcpy etc. My
> current thinking is to define a set of macros in the HAL,
> HAL_FLASH_{READ,WRITE}{8,16,32} and HAL_FLASH{COPY_FROM,COPY_TO} which
> would take an offset into the flash device (rather than a literal
> address which is what is currently used). For backward compatibility
> these macros could default back to directly accessing flash using direct
> pointer dereferences and memcpy on those platforms which have linear
> flash (that is, most of them). Once these macros were in place I would
> need to modify places which use flash to use them instead of directly
> accessing flash, this would include the flash drivers and the users
> (i.e. redboot).
> 
> Other options might be to create a full blown 'flash' device layer, or
> even better porting the Linux MTD to eCos. I haven't looked into this,
> so I'm not entirely sure this is possible  -- although JFFS2 has been
> ported so maybe it is.
> 
> So, what do the maintainers think of this plan -- what sort of solution
> would be most acceptable to you?
> 
> Cheers,
> Ian.
> 
> [0] The boards are like this to support ROM-DOS, it's a royal pain. But
> I'm stuck with it on several of our products since there was no room
> left to make Linear vs. Paged flash an option.

Yes, I've already thought about this and have a plan (but no time to
implement it)

FLASH 'writing' is already done via a function.  All we really need
is a function to read data.

I'd much prefer if your FLASH driver provided a virtual address
range (not virtual in the sense of MMU, just a range 0..N).  Then
make the read/write/erase functions work on this virtual offset.
They already work like this for everything except reading FLASH
data.

The only other thing would be to identify the [very small] handful
of places within RedBoot (or eCos) that access the FLASH directly.

Adding this support would also make it possible for RedBoot to
use NAND flash without too much trouble.

-- 
.--------------------------------------------------------.
|       Mind: Embedded Linux and eCos Development        |
|--------------------------------------------------------|
| Gary Thomas              email:  gary.thomas@mind.be   |
| Mind ( http://mind.be )  tel:    +1 (970) 229-1963     |
| gpg: http://www.chez-thomas.org/gary/gpg_key.asc       |
'--------------------------------------------------------'


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