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:

  1. RTOS Bootloader

  2. 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 FreeRTOS

  • In this case one would see below boot files in a SD card

    1. tiboot3.bin - this is the SBL which the ROM bootloader will boot on MCU R5F Core0

    2. tiboot3.bin will boot tifs.bin - this is the DMSC firmware binary

    3. tiboot3.bin will boot a file called “app” - this file contains binaries of all other CPUs like A72, Main R5F, C6x, C7x

    4. “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 LINK

The table below provides more information about the features and differences between the SBL bootloader and the MCUSW “CAN Boot App”:

Feature area

SBL Description

MCUSW “CAN Boot App”

Key Diffs / Comments

Initial Bootloader

YES

NO

MCUSW CAN Boot app is a “tertiary” bootloader

SoC’s Supported

AM65xx/J7200/J721E/J721S2/J784S4

J7200/J721E/J721S2/J784S4

Device types supported

GP, HS

GP, HS

NOTE: most, but not all, features are supported for each device type. Check specific feature support listed in each release.

Runs on MCU R5F

YES

YES

NOTE: the SBL is used to boot the MCUSW CAN Boot App

Can support startup with MCU domain only

YES

YES

Boot media supported

UART, MMCSD, OSPI

MMCSD, OSPI

UART boot supported with SBL only

Supports booting HLOS + RTOS images

YES

YES

SBL uses “combined appimage” build to put all RTOS & HLOS images into a single .appimage, whereas a specific format of combined images is used with the CAN boot app.

Boots another app to MCU R5F

YES

Boot app doesn’t support booting an app to the MCU R5F (since it is the app already running on that processor)

Early CAN response demo

NO

YES

Image Layout

single appimage

3-5 different appimages

SBL: all images for the remote cores to be booted must all be combined in to a single .appimage file that is either placed on the SD card (for MMCSD boot) or is flashed to a single flash addr location (for xSPI / OSPI boot). This includes all HLOS & RTOS images that must be booted.

MCUSW “CAN Boot App”: images for remote cores to be booted are split up into 3-5 different appimage files for either SD card booting or flashed into 3-5 different flash addresses for xSPI / OSPI booting (see details in the MCUSW CAN Boot App documentation).

Doc links

LINK

LINK

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/ti-u-boot-<version and git tag>

  • This is used when Linux runs on the A72. Most SDK demos like deep learning demos use Linux on the the A72 hence this bootloader is used in many out of box demos.

  • In this case one would see below files in the SD card

  1. tiboot3.bin - this is the SPL (not SBL) which the ROM bootloader will boot on MCU R5F Core0

  2. tiboot3.bin will boot tifs.bin - this is the DMSC firmware binary

  3. tiboot3.bin will boot tispl.bin on A72 - this is the 1st stage bootloader on A72 before uboot

  4. tispl.bin on A72 will boot uboot.img on A72 - this is uboot which will boot Linux

  5. 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-<cpu>-fw

  6. 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-proc-board-tps65917.dtb

  7. uboot.img will boot Linux kernel stored in rootfs partition below

    /boot/Image

  8. 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

8.2.4. Bootloaders Supported in Vision Apps

Vision Apps supports both Linux and QNX running on the A72. (For more information, see LINK).

Along with the support for each of these HLOS’s, Vision Apps provides a set of scripts which allow developers to quickly build and run with different bootloaders. A summary of these bootloader support for each of these builds can be seen in the table below:

HLOS

U-boot SPL

SBL MCUSW “CAN Boot App”

DM

Linux

YES (Default)

NO

Default DM with U-boot SPL is from PDK, but vision apps binary can be built using vision apps build flags

QNX

YES

YES (Default)

Default DM with U-boot SPL is from PDK, but vision apps binary can be built using vision apps build flags. For SBL MCUSW “CAN Boot App”, the boot app serves as the DM.

8.2.5. Bootloader Memory Map

Details about various bootloader components’ memory maps are provided below. This may be needed in the case that a custom bootloader needs to be created.

Component

Memory Map Location Link

R5 SPL

LINK

SYSFW

MCU1_0 Application Development with SYSFW

DMSC ROM

Please reference the Initialization Chapter of the Boot Memory Maps section of the TRM