Buildin emmc_all script

Referring https://github.com/nxp-imx/mfgtools/blob/master/uuu/emmc_burn_all.lst

bmap

A "block map" (bmap) of the image file, which essentially records which blocks of the file contain actual data and which are empty or contain only zeros.

https://github.com/yoctoproject/bmaptool

bmap-file is created by yocto, which speeds up the flashing process.

Bootloader extraction

Some commands can extract the bootloader from the wic image. This is done by using the "tag" at the end of the bootloader. If you’re building using yocto, there is the uuu_bootloader_tag.bbclass that does this: https://github.com/nxp-upstream/meta-freescale/blob/master/classes/uuu_bootloader_tag.bbclass

without the tag, uuu can’t automatically extract the bootloader and you have to explicitly supply it when calling uuu.

General workflow:

load u-boot (="_flash.bin") into the RAM (using SDP/SDPU/SDPV protocol) and execute it.
in the last block of the file, you see the "FB" lines. This is the Fastboot protocol. It originates from the Android project, but is just a generic protocol to communicate with the bootloader: https://docs.u-boot.org/en/latest/android/fastboot-protocol.html

Here, you can see two commands being used:

`ucmd`

which just calls u-boot commands like setenv and mmc: https://docs.u-boot.org/en/latest/usage/cmd/env.html (setenv `is an alias of `env set) https://docs.u-boot.org/en/latest/usage/cmd/mmc.html

`flash`

which writes data to the emmc:

_flash.bin is the bootloader image (earlier, we wrote it only to RAM, now, we write it to mmc,) _image is the actual image

EMMC bootloader partition

One more thing to note: the EMMC (or SD-card, which is similar) has "hardware partitions": https://www.pengutronix.de/en/blog/2020-10-15-anpassen-einer-emmc.html https://www.embeddedartists.com/wp-content/uploads/2020/04/Working_with_eMMC.pdf When booting from emmc, the i.mx looks at the bootpartition switch and boots from one of the two boot partitions.

when using the FB command to flash the bootloader into one of the eMMC’s boot partition, this command is used: FB: flash -scanterm -scanlimited 0x800000 bootloader _flash.bin

The string bootloader (or bootloader0) is hard-coded in NXP’s own u-boot branch, and tells their u-boot into which hardware-partition the data should be written to. https://github.com/nxp-imx/uboot-imx/blob/lf_v2025.04/include/fb_fsl.h #define FASTBOOT_PARTITION_BOOTLOADER "bootloader" this is used by NXP’s (formerly Freescale → FSL) fastboot implementation: drivers/fastboot/fb_fsl/fb_fsl_dev.c drivers/fastboot/fb_fsl/fb_fsl_boot.c drivers/fastboot/fb_fsl/fb_fsl_partitions.c

This always writes the bootloader to boot partition 1. So if you’re using mainline u-boot, take care because you might have to modify the uuu scripts.

In the end, there is then the call of the mmc partconf subcommand. https://docs.u-boot.org/en/latest/usage/cmd/mmc.html The boot_partition value is set to 1, which refers to Boot partition1 enabled for boot. (for older u-boot versions, partconf might be replaced by hwpartition instead)

For mainline u-boot, grep for these strings: EMMC_HWPART_BOOT, EMMC_BOOT_PART_, CONFIG_FASTBOOT_MMC_BOOT

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