4.13.3.16. NXP i.MX8MM EVK Evaluation Board

Board comes with:

  • 2GiB of LPDDR4 RAM

  • 16GiB eMMC

Not including booting via serial, the device can boot from either SD or eMMC.

4.13.3.16.1. Downloading DDR PHY Firmware

As a part of DDR intialization routine NXP i.MX8MM 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-8.0.bin
chmod +x firmware-imx-8.0.bin
./firmware-imx-8.0.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

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-8.0/firmware/ddr/synopsys/${f} \
            firmware/${f}; \
done

4.13.3.17. DDR Configuration Code

The following two files:

  • arch/arm/boards/nxp-imx8mq-evk/ddr_init.c

  • arch/arm/boards/nxp-imx8mq-evk/ddrphy_train.c

were obtained by running i.MX 8M DDR Tool that can be found here:

https://community.nxp.com/docs/DOC-340179

Only minimal amount of necessary changes were made to those files. All of the “impedance matching” code is located in “ddr.h”.

4.13.3.18. Build barebox

make imx_v8_defconfig make

4.13.3.19. Start barebox

The resulting image file is images/barebox-nxp-imx8mm-evk.img. Configure the board for serial download mode as printed on the PCB. You can start barebox with the imx-usb-loader tool that comes with barebox like this:

./scripts/imx/imx-usb-loader images/barebox-nxp-imx8mm-evk.img

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

  • The 32KiB preamble MMC preamble must be stripped.

  • 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.