8.2. Understanding bootloaders in Processor SDK J721E (RTOS/Linux)¶
8.2.1. Introduction¶
There are two bootloaders in Processor SDK J721E (RTOS/Linux). They are:
RTOS Bootloader
Linux Bootloader
This developer note describes about these two bootloaders.
8.2.2. RTOS Bootloader¶
RTOS Bootloader is referred to as SBL (Secondary bootloader).
This is included in Processor SDK RTOS at
pdk_<device>_<version>/packages/ti/boot
This is used when all cores on the SoC run SysBIOS
In this case one would see below boot files in a SD card
tiboot3.bin - this is the SBL which the ROM bootloader will boot on MCU R5F Core0
tiboot3.bin will boot tifs.bin - this is the DMSC firmware binary
tiboot3.bin will boot a file called “app” - this file contains binaries of all other CPUs like Main R5F’s, A72, C6x, C7x
“app” is created by running an offline tool which covert elf .out files to .rprc format and then combines these to something called “multi-core image”
See also
See this page for more info on this .rprc file and offline boot tools https://software-dl.ti.com/processor-sdk-rtos/esd/docs/latest/rtos/index_Foundational_Components.html#boot
8.2.3. Linux Bootloader¶
Linux bootloader uses SPL and uboot to boot various CPUs.
This is included in Processor SDK Linux at below path
board-support/u-boot-<version and git tag>
This is used when Linux runs on A72. Most SDK demos like deep learning demos use Linux on A72 hence this bootloader is used in many out of box demos.
In this case one would see below files in the SD card
tiboot3.bin - this is the SPL (not SBL) which the ROM bootloader will boot on MCU R5F Core0
tiboot3.bin will boot tifs.bin - this is the DMSC firmware binary
tiboot3.bin will boot tispl.bin on A72 - this is the 1st stage bootloader on A72 before uboot
tispl.bin on A72 will boot uboot.img on A72 - this is uboot which will boot Linux
uboot.img will boot non A72 (such as C6x, C7x, R5F) binaries located at below path in rootfs partition of the SD card
/lib/firmware/j7-main-<cpu>-fw
uboot.img will read a file uEnv.txt which will tell which .dtbo files to apply in addition to below dtb file present in rootfs partition
/boot/k3-<j721e|j7200>-proc-board-tps65917.dtb
uboot.img will boot Linux kernel stored in rootfs partition below
/boot/Image
Linux will use information in the loaded .dtb/dtbo files to configure itself during boot
Note
Steps 4-8 is standard Linux boot flow typical of any SoC.
Steps 1-3 are specific to J7 SoC.
See also
Refer to PSDK LINUX documentation for more information on uboot https://software-dl.ti.com/jacinto7/esd/processor-sdk-linux-jacinto7/latest/exports/docs/linux/Foundational_Components_U-Boot.html#u-boot-user-s-guide