[En-Nut-Discussion] olimex-sam7-ex256 mmc problem

[duane ellis]

Ole Reinhardt wrote:
>> I also wounder is there any way to check if the read partition part is ok?
>> I think that my problem lies there some whare. I will investigate that more
>> later in the week.
>>     
>
> I've also just seen sd cards formated without any partition at all!
> There was used the whole card without any partition table. This kind of
> formating won't be supported by NutOS. Could you try to run a fdisk on
> this card (perhaps using linux).
>
>   
I've been lurking on this thread for a while.

(a) I have quite a bit of knowledge with sd/mmc - though - not with spi 
mode.

(b) it is *common* to have sd/mmc cards both with and with-out partition 
tables.
    (older smaller cards tend to not have them - nothing is consistent!)

    Note that all SD/MMC cards are actually commodity items. Nobody makes
    the entire thing end to end - they buy up controller chips - and the 
cheapest
    flash chip - and have the cheapest factory assemble them. THEN - apply
    some brand name sticker. They all do this.

(c) SD/MMC cards commonly are implemented with NAND flash, NAND flash
    is error prone. You may know - hard drives are never 10G, due to bad 
spots.
    Same thing applies to SD/MMC cards.

(d) Many older SD/MMC cards have a rd/wr sector 0.

(e) Many - newer SD/MMC cards have a read-only sd/mmc cards.

(f) I do not know much about how > 2gig cards work.
    My knowledge is limited to <= 2gig cards.

(g) If you have not read the Microsoft FAT document - you should.
    It explains many "got-ya" problems many people have gotten *WRONG*.

    http://www.microsoft.com/whdc/system/platform/firmware/fatgen.mspx

    You can also google for: "*Microsoft* Extensible Firmware Initiative 
*FAT 32* *File System Specification"
*--

You might want to read these posts from my previous life.
(I worked for an ebook maker - our ebook readers had sd/mmc slots)

Note that these emails describe using an SD/MMC controller - in SD/MMC 
mode, not SPI mode.
That said - you may find some useful things.

    http://www.spinics.net/lists/arm/msg11428.html

    http://www.spinics.net/lists/arm/msg10774.html

    http://www.spinics.net/lists/arm/msg10775.html

--

In the 1st email (11428 link above) - step #4 describes how to test if 
you have an SD or MMC card by sending different commands to the card.

The same auto-detect technique works in SPI mode.

-Duane.