Freescale i.MX is traditionally very well supported under barebox. Depending on the SoC, there are different Boot Modes supported. Older SoCs up to i.MX31 support only the external Boot Mode. Newer SoCs can be configured for internal or external Boot Mode with the internal boot mode being the more popular mode. The i.MX23 and i.MX28, also known as i.MXs, are special. These SoCs have a completely different boot mechanism.
The Internal Boot Mode is supported on:
With the Internal Boot Mode, the images contain a header which describes where the binary shall be loaded and started. These headers also contain a so-called DCD table which consists of register/value pairs. These are executed by the Boot ROM and are used to configure the SDRAM. In barebox, the i.MX images are generated with the scripts/imx/imx-image tool. Normally it’s not necessary to call this tool manually, it is executed automatically at the end of the build process.
The images generated by the build process can be directly written to an SD card:
# with Multi Image support:
cat images/barebox-freescale-imx51-babbage.img > /dev/sdd
# otherwise:
cat barebox-flash-image > /dev/sdd
The above will overwrite the MBR (and consequently the partition table) on the destination SD card. To preserve the MBR while writing the rest of the image to the card, use:
dd if=images/barebox-freescale-imx51-babbage.img of=/dev/sdd bs=512 skip=1 seek=1
The images can also always be started second stage:
bootm /mnt/tftp/barebox-freescale-imx51-babbage.img
Most boards can be explicitly configured for USB Boot Mode or fall back to USB Boot when no other medium can be found. The barebox repository contains a USB upload tool. As it depends on the libusb development headers, it is not built by default. Enable it explicitly in make menuconfig and install the libusb development package. On Debian, this can be done with apt-get install libusb-dev. After compilation, the tool can be used with only the image name as argument:
scripts/imx/imx-usb-loader images/barebox-freescale-imx51-babbage.img
The External Boot Mode is supported by the older i.MX SoCs:
(It may be supported on newer SoCs as well, but it is not widely used there.)
The External Boot Mode supports booting only from NOR and NAND flash. On NOR flash, the binary is started directly on its physical address in memory. Booting from NAND flash is more complicated. The NAND flash controller copies the first 2kb of the image to the NAND Controller’s internal SRAM. This initial binary portion then has to:
It is possible to write the image directly to NAND. However, since NAND flash can have bad blocks which must be skipped during writing the image and also by the initial loader, it is recommended to use the barebox_update - update barebox to persistent media command for writing to NAND flash.
Not supported all boards have a description here. Many newer boards also do not have individual defconfig files, they are covered by imx_v7_defconfig or imx_defconfig instead.