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 tiboot3.bin, tispl.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

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