Bootloader Boot Source Support; Bootloader Boot Counter; Table 15: Environment Variables For "Boot_Sel - Kontron SMARC-sAMX8 User Manual

7.10. Bootloader Boot Source Support

The SMARC v2.0 Specification defines three boot select signals BOOT_SEL[0:2]# that allows the user to select from
eight possible boot devices. On the SMARC_sAMX8X, U-Boot detects the BOOT_SEL signals from the carrier and sets
the environment variable "boot_sel" as shown below.

Table 15: Environment Variables for "boot_sel"

BOOT_SEL2# BOOT_SEL1#
GND GND
GND GND
GND Float
GND Float
Float GND
Float GND
Float Float
Float Float
(1) The SMARC sAMX8 does not support these modes
Bootloader environment scripts can use the boot_sel environment variable to select the source where the dedicated OS
image can be loaded. As an example, the bootloader environment of the SMARC_sAMX8 implements some small
scripts that will load a linux system from the boot source as defined by the BOOT_SEL pins.
bootsel_boot=echo BOOT_SEL ${boot_sel} selected && run ${boot_sel}_boot
module_spi_boot=run module_mmc_boot
module_mmc_boot=setenv mmcdev 0; run mmcboot
carrier_sd_boot=setenv mmcdev 1; run mmcboot
remote_boot=run netboot
Running the "run bootsel_boot" script will load a linux system from MMC if BOOT_SEL pins define the module MMC
Flash or the Module SPI as boot source. Depending on application, the script variables in environment can be adapted.
The bootloader is always booted from the boot source defined by fuse settings, which is
normally the QSPI flash device. The BOOT_SEL pins only define boot source for the OS.

7.11. Bootloader Boot Counter

U-Boot on the SMARC_sAMX8 module will read the current boot counter value and increment it on every boot cycle.
Current boot counter is shown as part of the information shown by the "kboardinfo" command (see description of
kboardinfo).
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BOOT_SEL0# boot_sel
GND carrier_sata (1)
Float carrier_sd
GND carrier_mmc (1)
Float carrier_spi (1)
GND module_device (1)
Float remote
GND module_mmc
Float module_spi
Kontron SMARC-sAMX8 - Rev. 1.2
Boot Source
Carrier SATA
Carrier SD Card
Carrier eSPI (CS0#)
Carrier SPI (CS0#)
Module Device (NAND, NOR) –
vendor specific
Remote boot (GBE, serial) –
vendor specific
Module eMMC Flash
Module SPI
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