3.1.1.9. UART¶
This section documents how to use the UART to load files to boot the board into U-Boot. After that the user is expected to know how they want to continue loading files.
3.1.1.9.1. Booting U-Boot from the console UART¶
In some cases we support loading SPL and U-Boot over the console UART. You will need to use the spl/u-boot-spl.bin and u-boot.img files to boot. As per the TRM, the file is to be loaded via the X-MODEM protocol at 115200 baud 8 stop bits no parity (same as using it for console). SPL in turn expects to be sent u-boot.img at the same rate but via Y-MODEM. An example session from the host PC, assuming console is on ttyUSB0 and already configured would be and the lrzsz package is installed
$ sx -kb /path/to/u-boot-spl.bin < /dev/ttyUSB0 > /dev/ttyUSB0
$ sx -kb --ymodem /path/to/u-boot.img < /dev/ttyUSB0 > /dev/ttyUSB0
In K3 based platforms, ROM supports booting from MCU_UART0 via X-Modem protocol. The entire UART-based boot process up to U-Boot (proper) prompt goes through different stages and uses different UART peripherals as follows:
WHO |
Loading WHAT |
HW Module |
Protocol |
|---|---|---|---|
Boot ROM |
tiboot3.bin |
MCU_UART0 |
X-Modem |
R5 SPL |
sysfw.itb |
MCU_UART0 |
Y-Modem |
R5 SPL |
tispl.bin |
MAIN_UART0 |
Y-Modem |
A53/A72 SPL |
u-boot.img |
MAIN_UART0 |
Y-Modem |
UART_BOOT_MAIN_UART and UART_BOOT_MCU_UART should be set to serial ports such as /dev/ttyUSBx.
$ sb --xmodem $OUT_R5/tiboot3.bin > $UART_BOOT_MCU_UART < $UART_BOOT_MCU_UART
$ sb --ymodem $SYSFW_ITB > $UART_BOOT_MCU_UART < $UART_BOOT_MCU_UART
$ sb --ymodem $OUT_AXX/tispl.bin > $UART_BOOT_MAIN_UART < $UART_BOOT_MAIN_UART
$ sb --ymodem $OUT_AXX/u-boot.img > $UART_BOOT_MAIN_UART < $UART_BOOT_MAIN_UART