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Original question:

[FAQ] AM64x/AM62x SoC redundant/recovery boot support in ROM booting R5 bootloader

AM6442: How does backup boot mode work, testing with AM64x EVM

Dominik Fischer
Intellectual 480 points

Tool/software:

Hi TI-Experts,

I have problems understanding how backup boot mode works/how I can trigger falling into this backup boot mode. Originally in our application we intend to boot in xSPI mode and fallback to SD-Boot if necessary. If read the corresponding parts in chip documentation and saw the following bootmode pin mapping table:

According to this the correct settings would be the following: 00 1 101 100 1110 011

This will primarily boot in xSPI mode and as fallback SD-Boot will be configured.

I tested on AM64x-EVM board. I did the setup for SD-Card and OSPI Flash from here: https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/latest/exports/docs/api_guide_am64x/EVM_SETUP_PAGE.html
If setting the corresponding types as primary boot modes everything works as expected. I get the expected outputs on UART.

Then I wanted to test backup boot mode:
- I deleted the whole flash (so that there is no valid tiimage/SBL anymore in OSPI)
- I selected the BOOTMODE Pin config as stated above (00 1 101 100 1110 011)
- I would then expect to get the same output as a normal boot on SD, but I did not get anything?

Am I testing wrong? How can I trigger a fallback to backup boot mode? Can this be triggered directly by SBL also?
Kind regards
Dominik
  • 0
    Intellectual 480 points

    I am now able to successfully fall back to SBL Null on SD-Card with this DIP switch setting:

    The backup boot mode works as expected if there is no image on Flash.

    Now I just need to find out if I can fallback from SBL OSPI also or if it is only allowed directly from RBL before SBL even started:

  • 0 in reply to Dominik Fischer
    TI__Genius 12980 points

    Hi Dominik,

    Glad to know it worked. What was the issue before? The previously shared boot mode looks same as the picture.

    Dominik Fischer said:
    Now I just need to find out if I can fallback from SBL OSPI also or if it is only allowed directly from RBL before SBL even started

    Yes, the primary and backup boot media option is read by ROM bootloader from the boot mode pin settings.

    This cannot be supported from SBL. For SBL, the user can pre-decide and flash the binaries into the required boot media. There are separate SBL examples to support each of them.

    Regards,
    Aparna

  • 0 in reply to Aparna Patra
    Intellectual 480 points

    Hi Aparna,

    Yes they are the same, however I had a problem with Micro-USB cable, but it seems to work as expected on AM64x-EVM now.

    Alright good to know, then we need to cope differently with the situation. We planned to use a modified version of SBL OSPI and if there are any problems in loading a valid application image we wanted to fall back to backup boot mode. But as far as I understand now this will not be possible, is this correct?

    It will only be possible if the SBL OSPI itself would delete the flash at offset 0x0 (delete itself), then after next powercycle we will enter backup boot mode

  • +1 in reply to Dominik Fischer
    TI__Genius 12980 points

    Yes, your understanding is correct.

    You can refer the SBL code and make modifications according to your requirements.

    Regards,
    Aparna

  • 0 in reply to Aparna Patra
    Intellectual 480 points

    Thanks for your help this issue can be closed for now