Partition types on eMMC and/or microSD

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1

I'm still wondering about why my BBB won't boot from a microSD card.

I currently have a (supposedly) bootable microSD image plugged into my
BBB and running fdisk I see the following:-

    root@odin:~# fdisk -l

    Disk /dev/mmcblk0: 14.7 GiB, 15720251392 bytes, 30703616 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0xac0cd885

    Device Boot Start End Sectors Size Id Type
    /dev/mmcblk0p1 * 8192 1740799 1732608 846M 83 Linux

    Disk /dev/mmcblk1: 3.6 GiB, 3867148288 bytes, 7553024 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x00000000

    Device Boot Start End Sectors Size Id Type
    /dev/mmcblk1p1 * 2048 198655 196608 96M e W95 FAT16 (LBA)
    /dev/mmcblk1p2 198656 7553023 7354368 3.5G 83 Linux

    Disk /dev/mmcblk1boot1: 2 MiB, 2097152 bytes, 4096 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk /dev/mmcblk1boot0: 2 MiB, 2097152 bytes, 4096 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    root@odin:~#

This seems wrong to me. The eMMC is /dev/mmcblk1 and (because it's an
old system) has a separate boot patition which is FAT16. As I
understand it reading the boot sequence the boot parititon *must* be
FAT12, FAT16 or FAT32.

My supposedly bootable microSD card image is a single partition (OK)
/dev/mmcblk0p1 *but* it's a Linux partition not a FAT one. Is this my
fundamental problem? I need to format the microsSD as FAT rather than
Linux?
dddd

2

See Slide 8:

https://docs.google.com/presentation/d/1ylRm_dhX8jgWLHhoXH3zLXQgETY1eYh_PXyhtD6_vPo/edit#slide=id.g2ab414fa36_0_105

Your old image is booting by the file marked "MLO", where as the image
is using the circled "Raw Mode"..

Raw Mode allows use to use single partition, and "anything" u-boot
directly supports:

currently: ext2/ext3/ext4/btrfs

Regards,

3

Thanks (again!) Robert. I'll need to read more closely through the
ROM boot sequence logic.

Is it possible that as my eMMC is booting via the old FAT + 'MLO' this
happens 'before' the normal choice between eMMC and microSD in raw
mode?

I've taken a more careful read through the boot sequence to see
and it certainly *looks* as if an SD card in raw mode should be
used in preference to eMMC. So maybe I do have a hardware fault.

4

Thanks (again!) Robert. I'll need to read more closely through the
ROM boot sequence logic.

Is it possible that as my eMMC is booting via the old FAT + 'MLO' this
happens 'before' the normal choice between eMMC and microSD in raw
mode?

I've taken a more careful read through the boot sequence to see
and it certainly *looks* as if an SD card in raw mode should be
used in preference to eMMC. So maybe I do have a hardware fault.

For the BBB, the bootrom looks at the eMMC BEFORE the microSD.

Unless you properly hold down the "boot" button*, before you plug in
any power to the board, then the microSD will be first..

* the sysboot pins are sampled early, even stray voltage from a few
seconds prior can cause randomness on the "boot" pin.. So let it
discharge a few seconds..

Regards