Re: Flashboard questions...

I know this -- Now.  I wasn't sure how the board interfaces worked for sure.

But my point still stands...  There is no reason we can't come up with a new 
image -- Program it to some kind of memory -- mod a Rom board to have a 
socket of some type -- and program the memory outside the board -- then 
use it in the 720.  Hey it may not be read/writable -- but its better than waiting 
for this mystical flashboard to appear.

You guys seem willing to just sit back and wait rather than actually 
attempting other solutions...

I just trying to get the creative juices flowing here...

On 8 Nov 2006 at 20:18, June Tate-Gans wrote:

The WRT54G is addressing the card in a serial manner through some
other native interface on the boards (in their case, they're using the
GPIO pins on the CPU -- something we don't have direct access to
through the ROM board).

The trick here is that the ROMs act as main system memory -- they are
directly addressable by the CPU as a memory space (which,
incidentally, is why Linux can't boot after a shutdown or reboot --
memory address 0x00000000 is literally the beginning of the ROM), and
we do not have the niceties of GPIO pins to prepare and use the SD
card before the CPU turns on/while it's running.

To integrate SD/MMC cards into the Jornada's architecture would
require all kinds of weird workarounds because SD/MMC memory is
accessed serially instead of directly like traditional RAM. The SD/MMC
design requires you to send several things all in serial:

  1. Send the SD/MMC card address
  2. Send the address offset in the SD/MMC
  3. Send/recieve your data

Note that before you can even approach this, you have to have
/assigned/ the address to the SD/MMC card before you can really talk
to it. Keep in mind that this is the only /feasable/ way you can talk
to an SD/MMC card -- there is no other cost effective method (native
SD mode costs mucho $$$ and still isn't a solution that is viable
since it's also not directly addressable). CF cards, on the other
hand, have similar issues as they are literally designed to emulate
the ATA interface provided by PCMCIA in a smaller package -- which is
why you can stick a CF into a PCMCIA card reader and read it just like
a typical ATA disk.

Traditional addressable memory is addressed in a much simpler fashion:

  - Write the address to the address portion of the memory bus
  - Read/write your data

Note that both of these operations typically happen in the same CPU
cycle, whereas the SD/MMC method would require several cycles to
complete. Because of this fundamental difference, you would likely end
up with timing issues as well. Keep in mind, I'm not saying it's
impossible, but it would be considerably more complex than using a set
of flash chips built onto a new board, and would be much less stable.

On 11/8/06, Chris Davis <[email protected]> wrote:
> Ok, but you are missing my point, then..  There are different modes of connecting memory cards to devices than ide.  Just look at the Linksys wrt54g SD card mod.  That router DOES NOT have anything resembling a IDE/ATA interface.
>
> While Compact flash is based on a IDE type interface, SD cards are not.
>
> -------------
> Subject: RE: [jornada] Flashboard questions...
>    From: "Tim Underwood" <[email protected]>
>    Date: Wed, 8 Nov 2006 12:24:48 -0600
>      To: <[email protected]>
>
> To use a SD/CF/etc card requires an ATA interface.
>
> Simply not available on the ROM board or flash board.  That's a whole
> different animal.  The ROM/mem board is just that - memory.  The OS does
> some magic to make the ROM magically appear in RAM (kinda similar to a
> RAM disk - but it isn't).
>
> To read/write mem cards is completely different, and a completely
> different circuit and interface methodology.  You can't just unsolder
> the ROM, and solder on a connector to put in an SD/CF/whatever card.
>
>
>
>
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>


-- 
June Tate-Gans    | Don't try to outweird me, three-eyes. I get stranger things
www.theonelab.com | than you free with my breakfast cereal. -- Zaphod Beeblebrox