Kontron SMARC-sAMX8 - Rev. 1.2
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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# BOOT_SEL0#
boot_sel
Boot Source
GND
GND
GND
carrier_sata (1)
Carrier SATA
GND
GND
Float
carrier_sd
Carrier SD Card
GND
Float
GND
carrier_mmc (1)
Carrier eSPI (CS0#)
GND
Float
Float
carrier_spi (1)
Carrier SPI (CS0#)
Float
GND
GND
module_device (1)
Module Device (NAND, NOR) –
vendor specific
Float
GND
Float
remote
Remote boot (GBE, serial) –
vendor specific
Float
Float
GND
module_mmc
Module eMMC Flash
Float
Float
Float
module_spi
Module SPI
(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).
