Phytec L-1017e.A3 i.MX 8M Plus, Руководство пользователя

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L-1017e.A3 i.MX 8M Plus BSP Manual
Set ${overlays} variable
The ${overlays} U-Boot environment variable contains a space-separated list of overlays that will be applied during
boot. Depending on the boot source the overlays have to either be placed in the boot partition of eMMC/SD-Card or
are loaded over tftp. Overlays set in the $KERNEL_DEVICETREE Yocto machine variable will be automatically added
to the boot partition of the final SD Card image.
The ${overlays} variable can be either set directly in the U-Boot environment. Or be a part of the external
bootenv.txt environment. The ${overlays} variable loaded from the external environment will always overwrite the
value from the environment saved directly in the flash. On default, the ${overlays} variable is not set directly in the
U-Boot environment but comes from the external bootenv.txt environment file. It is also located in the boot
partition of the sdcard image. You can read and write the file on booted target:
target$ cat /boot/bootenv.txt
overlays=imx8mp-phyboard-pollux-peb-eval-
01 .dtbo imx8mp-phyboard-pollux-peb-av- 010 .dt
bo
Changes will then take effect after the next reboot. If no bootenv.txt file is available the overlays variable can be set
directly in the U-Boot environment.
u-boot=> setenv overlays imx8mp-phyboard-pollux-peb-av- 010 .dtbo
u-boot=> printenv overlays
overlays=imx8mp-phyboard-pollux-peb-av-
010 .dtbo
u-boot=> saveenv
More information about the external environment can be found in U-boot External Environment .
We use the ${overlays} variable for overlays describing expansion boards and cameras that can not be detected
during run time. To prevent applying overlays listed in the ${overlays} variable during boot the ${no_overlays}
variable can be set to 1 in the bootloader environment.
u-boot=> setenv no_overlays 1
u-boot=> saveenv
Extension Command
The u-boot extension command makes it possible to easily apply overlays that have been detected and added to a
list by the board code callback
extension_board_scan() . In the BSP, the overlays applied in this way are used to
disable components that are not populated on the SoM. The detection is done with the EEPROM data (EEPROM SoM
Detection) found on the SoM i2c EEPROM.
The detection is so far implemented for SPI-NOR flash and ethernet PHY. It depends on the SoM variant if any device
tree overlays will be applied. To check if an overlay will be applied on the running SoM run:
u-boot=> extension scan
Found
1 extension board(s).
u-boot=> extension list
Extension
0 : phyCORE-i.MX8MP no SPI flash