4.13.3.21. NXP i.MX8MN EVK Evaluation Board

Board comes with either:

• 2GiB of LPDDR4 RAM

• 2GiB of DDR4 RAM

barebox supports both variants with the same image.

4.13.3.21.1. Downloading DDR PHY Firmware

As a part of DDR intialization routine NXP i.MX8MN EVK requires and uses several binary firmware blobs that are distributed under a separate EULA and cannot be included in Barebox. In order to obtain them do the following:

wget https://www.nxp.com/lgfiles/NMG/MAD/YOCTO/firmware-imx-8.12.bin
chmod +x firmware-imx-8.12.bin
./firmware-imx-8.12.bin

Executing that file should produce a EULA acceptance dialog as well as result in the following files:

• lpddr4_pmu_train_1d_dmem.bin

• lpddr4_pmu_train_1d_imem.bin

• lpddr4_pmu_train_2d_dmem.bin

• lpddr4_pmu_train_2d_imem.bin

• ddr4_dmem_1d_201810.bin

• ddr4_imem_1d_201810.bin

• ddr4_dmem_2d_201810.bin

• ddr4_imem_2d_201810.bin

As a last step of this process those files need to be placed in “firmware/”:

for f in lpddr4_pmu_train_1d_dmem.bin  \
         lpddr4_pmu_train_1d_imem.bin  \
         lpddr4_pmu_train_2d_dmem.bin  \
         lpddr4_pmu_train_2d_imem.bin; \
do \
         cp firmware-imx-8.12/firmware/ddr/synopsys/${f} \
            firmware/${f}; \
done

for f in ddr4_dmem_1d_201810.bin  \
         ddr4_imem_1d_201810.bin  \
         ddr4_dmem_2d_201810.bin  \
         ddr4_imem_2d_201810.bin; \
do \
         cp firmware-imx-8.12/firmware/ddr/synopsys/${f} \
            firmware/${f%_201810.bin}.bin; \
done

4.13.3.22. Build barebox

make imx_v8_defconfig make

4.13.3.23. Installing barebox

When the EVK is strapped to boot from eMMC, the i.MX8M bootrom will consult the eMMC ext_csd register to determine whether to boot from the active eMMC boot partition or from the user area.

The same barebox image written to the start of the SD-Card can be written to the start of the eMMC user area. Power-fail-safe installation to the eMMC boot partition requires special handling:

• The barebox image must be written to the inactive boot partition, then afterwards, the newly written boot partition is activated (This is controlled by the barebox mmcX.boot variable).

• The barebox image includes a 32KiB preamble that allows the image to be directly writable to the start of the SD-Card or eMMC user area. Unlike older i.MX8M, the i.MX8MN BootROM expects the bootloader to not start at an offset when booting from eMMC boot partitions, thus the first 32KiB must be stripped.

The following steps are required to write the image to the QSPI NOR flash:

• Strip the 32KiB preamble, like it is done for the eMMC boot partition case (see above).

• The QSPI NOR partition barebox must be erased before the stripped image is written. The erase size depends on the stripped image size but always start at offset 0.

• Write the stripped barebox image to the QSPI NOR partition barebox at offset 0.

The barebox_update command takes care of this and need just be supplied a barebox image as argument.