CM-FX6: U-Boot: Building Images

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CM-FX6 firmware consists of two components: Secondary Program Loader (SPL) and U-Boot. Both components are based on U-Boot source code. SPL is the bootstrap utility invoked by the CPU internal boot ROM code of the i.MX6 SoC. SPL performs minimal hardware initialization and loads U-Boot from the same boot device. U-Boot initializes hardware modules necessary for system boot and loads the operating system.

Building Firmware images for CM-FX6


There are several options for cross-compilation toolchain setup. You can either compile your cross-compiler or use an already built cross-compiler. The cross-compiler should support the ARM embedded-application binary interface (EABI)

  • Pre-built toolchain (recommended):
  • Tools for creating cross-compilers:
    • Crosstool-ng: Builds a cross-compiler from source. Non-distribution specific.
    • Crossdev: Gentoo's cross-compiler builder. Needs Gentoo.

Getting U-Boot sources

There are two ways to get U-Boot sources that can be used as a baseline for CM-FX6 SPL and U-Boot. You can create a copy of "Das U-Boot" source tree or download a snapshot and extract it. We assume that you have created /home/development/cm-fx6/u-boot directory for CM-FX6 u-boot development.

Snapshot download

  • Download v2015.07 snapshot with your web browser.
  • Extract the downloaded archive u-boot-33711bd.tar.gz
cd /home/development/cm-fx6/u-boot
tar xvf /path/to/downloaded/u-boot-33711bd.tar.gz
mv u-boot u-boot-cm-fx6
This will create /home/development/cm-fx6/u-boot/u-boot-cm-fx6 directory containing U-Boot source code tree.
  • Apply the CM-FX6 patch
cd /home/development/cm-fx6/u-boot/u-boot-cm-fx6
patch -p1 < /path/to/cm-fx6-u-boot-package/u-boot/u-boot-v2015.07-cm-fx6-3.patch

Git clone

  • Install git version control system.
  • Create a clone of U-Boot tree
cd /home/development/cm-fx6/u-boot
git clone git:// u-boot-cm-fx6
cd /home/development/cm-fx6/u-boot/u-boot-cm-fx6
  • Create a branch for CM-FX6 development. The CM-FX6 patches are generated vs. v2015.07 tag (33711bdd4a4dce942fb5ae85a68899a8357bdd94 commit) in the U-Boot tree. It is recommended to use exactly the same baseline to avoid merge conflicts.
git checkout -b cm-fx6-dev v2015.07
  • Apply the CM-FX6 patch
git apply /path/to/cm-fx6-u-boot-package/u-boot/u-boot-v2015.07-cm-fx6-3.patch

Building the firmware images

  • First, compile both SPL and U-Boot. The following commands create the spl/u-boot-spl.bin and u-boot.img binaries (along with other image types):
export ARCH=arm
export CROSS_COMPILE=arm-none-linux-eabi-
make mrproper
make cm_fx6_config && make
  • Invoke mkimage on the SPL binary to attach the IVT header required by the i.MX6 boot ROM code to the SPL binary. This generates a new image file spl.img.
./tools/mkimage -n arch/arm/imx-common/spl_sd.cfg.cfgtmp -T imximage -e 0x00908000 -d spl/u-boot-spl.bin spl.img
  • Create the combined image by creating a 0xFF initialized 512KB cm-fx6-firmware file, and writing the spl.img and u-boot.img data to the appropriate offsets within the firmware file.
dd if=/dev/zero count=500 bs=1K | tr '\000' '\377' > cm-fx6-firmware
dd if=spl.img of=cm-fx6-firmware bs=1K seek=1 conv=notrunc && dd if=u-boot.img of=cm-fx6-firmware bs=1K seek=64 conv=notrunc
  • You can now install the cm-fx6-firmware file into an SD card or CM-FX6 SPI flash.

See also