>>   echo "This is in flash" > /boot/foo
>>   cat /boot/foo
> Yes, but it is from a userspace
>
> What I would like to achieve is writing to flash from "outside".
> For example JTAG is an example.
> Via JTAG you can write to flash( using  for example DMA - direct
> memory  access).
> But to be able to do so, I must know the flash location.

You indicated that the flash was the device the OS is located on, so it is
a block structured device.  While block structured devices can, and
sometimes are, implemented in memory, it probably wouldn't make sense for
the OS.  More likely it is SPI flash.

I believe you also indicated (although I couldn't find the reference) that
the flash was an SD card.

Both of these are indications that the flash is not in the address space.=20
An SD card is an SPI device.  It does not have an address range that you
can write simply by providing data to the appropriate addresses.  Even if
it is just a flash chip it is more likely to be SPI than parallel since it
is not only cheaper but requires less real estate.

Even parallel flash typically requires a protocol not quite like RAM,
especially for writing.  Flash, unlike RAM, is considerably slower writing
than reading.  Furthermore, unless the flash is very small, it most likely
requires writing blocks, rather than bytes, at a time.

SPI requires a communications protocol not unlike a hard disk.  If it
shows up in the address space at all it is only two or three locations,
not the thousands you are looking for,

Since you have no RAM other than the SDRAM, that almost certainly starts
at zero and extends for as much as you have, unless, of course, you have
memory on the processor (as in a PIC).

--McD


--=20
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