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memory booting via MMC/SD in raw mode

burchmere
Intellectual 930 points

Regarding booting in "raw mode", the TRM specifically states that it looks in sector 0 of the MMC/SC card for a valid Configuration Header.  In this case, is the only required CH TOC entry "CHMMCSD", or are other TOC entries required?  And must the "section address" value of the TOC entry be on a sector boundary or could it actually be immediately following the CH (and still within sector 0)?

 

  • TI__Mastermind 41665 points

    In general I would suggest just avoiding the raw mode all together, because this means you have to have a SD card that does not have a proper file system on it, you would be reading directly out of the SD card as if it were directly connected NAND or NOR flash.

    My understanding of if you were to attempt this would be that the configuration header would also need to have a MLO or a CHSETTINGS item so that the raw mode would be entered by the ROM boot loader. I imagine you could just access the addresses following the CH in sector 0, however unfortunately I have never seen this mode used so I could not say for sure if some other sector limitation is in play.

    I am curious what kind of geometry you require on the SD card for your application, why would you want to use a non standard SD card boot setup?

  • in reply to Bernie Thompson TI
    Intellectual 930 points

    It's unlikely I would go with raw mode booting but wanted to understand how it works.  The reason I'm asking is that we're looking to use embedded MMC flash (eMMC) as the only flash memory on the device.  Normally this type of flash would be partitioned and formatted for use entirely as a filesystem(s).  However, we have requirements for non-volatile storage outside of any filesystem - storage that would have typically been handled by a sector or two of NAND or NOR flash.  So I'm looking at perhaps a non-standard partitioning of the eMMC to achieve this, but it's completely internal to our system - not for an external SD card.  (And since we'll have this "non-filesystem" space, I wanted to understand whether the OMAP could boot from it or not.)

     

  • in reply to burchmere
    TI__Mastermind 41665 points

    You should be able to partition the card such that there was blank unused space beyond where your proper file system partitions are, you would just have to ensure that the empty partition was not first so that your primary bootable partition still works like normal. Of course I have not tried this myself, but I suspect you could make smaller partitions and have leftover space on the card and still boot.