Since this tiny application is written in assembly and make no use of any
toolchain-provided header or libraries (not even startfiles), you can use
basically any arm-gcc toolchain. By default it expects an arm-linux-gnueabihf
toolchain to be installed, but you can override this in the makefile or using a
CROSS_COMPILE= argument to make.
Output files produced are:
demo.elfsuitable for JTAG upload and debuggingdemo.binsuitable for peripheral boot (UART, Ethernet, USB) and XIPdemo.MLOsuitable for memory boot (μSD, eMMC, SPI, NAND)demo.imgsuitable for writing directly to μSD or eMMC
Boot ROM checks for the presence of a raw mmc boot header in sectors 0, 256, 512, and 768. If found, it expects the MLO to be located starting at the next sector. If none of the four locations have a valid image, ROM proceeds to check for a FAT filesystem (either whole-card or in a partition marked 'active'/bootable). The MLO should be located in a file named "MLO" in the root of the filesystem.
Note: Contrary to what the AM335x TRM used to indicate (prior to rev M), raw MMC boot also works for SD cards, not just for eMMC.
Caution: This destroys existing contents of the card.
dev=/dev/mmcblk0
dd if=demo.img of=$devCaution: This overwrites sectors 1 and 2 of the card and may overwrite any existing bootloader. It should not affect any existing partitions that start at sector 3 or higher.
dev=/dev/mmcblk0
sector=0
dd if=extra/raw-mmc-header.img of=$dev seek=$sector
dd if=demo.MLO of=$dev seek=$(( $sector + 1 ))Note: a raw MMC header in sector 0 can peacefully coexist with a partition table, provided adequate free space is available between the partition table and the first partition to accomodate the MLO data. The procedure above will not damage any existing partition table, nor should the raw mmc header get damaged by repartitioning.
Caution: This destroys existing contents of the card.
dev=/dev/mmcblk0
mountpoint=/mnt/tmp
echo "type=0c,bootable" | sfdisk $dev
mkfs.fat ${dev}p1
mount ${dev}p1 $mountpoint
cp demo.MLO $mountpoint/MLO
umount $mountpointBoot ROM tries to download a peripheral boot image using BOOTP and TFTP. See
extra/dnsmasq.conf for an example configuration for dnsmasq, which can
perform both functions at the same time.
In case of USB, the device enumerates as an RNDIS network interface, after which it proceeds the same as Ethernet.