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when using flash based serial bootloader provided as an example project, how to trigger to enter the serial bootloder mode using only UART Tx and Rx pins?

Ji-won Lee
Genius 3630 points

Hi TI experts,

As I understand, to enter ROM based serial bootloader under a valid image is running, a backdoor pin and the related level must be monitored and handled.

But, in my case, our BLE module will have only UART Tx and Rx pins with an external host MCU.

The reference application example for flash based bootloader also is using the PIN_BL_ENTER as a backdoor pin with a level as a trigger.
If I just can use UART Tx & Rx pins, how to trigger to enter the flash based serial bootloader?

If no problem to modify the reference code to check the pin, can I assign the UART Tx pin to general IO pin with input direction mode and then monitor the pin's level being driven with low signal by the external host MCU ?

Of course, after triggered and entered the mode, I will assign the UART Tx pin to output direction mode.

Up to here, my question is with respect to flash based bootloader.

from here, I would like to ask the same concept on ROM based bootloader.

As "the backdoor pin configuration matches one of the UART0 or SSI0 pins" mentioned, again, could the UART Tx pin be switched to a general IO pin with temporarily input direction mode as the backdoor pin for ROM based bootloader too? or UART Rx pin only could be available for it?

If possible, ROM based bootloader is better than flash based bootloder to make user application area to have more area of flash memory.

Thanks in advance,
Ji Won

  • 0
    TI__Mastermind 33460 points

    Ji Won,

    It seems that most of your questions actually pertain to the ROM based bootloader (CCFG changes, BL backdoor pins, etc) so let's cover that first.

    Q: As I understand, to enter ROM based serial bootloader under a valid image is running, a backdoor pin and the related level must be monitored and handled.

    A: Yes in general there are two ways to enter the ROM bootloader, either by modifying the IMAGE_VALID_CONF in the CCFG to be non zero or by enabling the BL back door and setting its pin via the CCFG in the BL_CONFIG field.

    Q: As "the backdoor pin configuration matches one of the UART0 or SSI0 pins" mentioned, again, could the UART Tx pin be switched to a general IO pin with temporarily input direction mode as the backdoor pin for ROM based bootloader too? or UART Rx pin only could be available for it?

    A: I think what you are asking here is whether or not you can have a two wire interface (UART TX, RX)  between your external MCU and the ROM bootloader. Yes, this is in fact possible. You would do so in the following way:

    1. Configure the CCFG to enable the BL_BACKDOOR, set the backdoor pin to match one of the two pins on your external MCU
    2. During the reset sequence on your external MCU be sure to initialize these pins such that you do not accidentenally put the CC26xx in BL mode
    3. Perform UART traffic as normal
    4. When you need to enter BL mode. Close the UART interface on your external MCU and use these PINs as GPIOs to perform the backdoor sequence to put the CC26xx in ROM bootloader mode
    5. Close the GPIO pins and initialze them back as UART and start sending commands to Boot load the CC26xx.

    Since you have identified the ROM based bootloader as your preference, lets' cover this topic first and see if it works for you before discussing the flash bootloader.

  • 0 in reply to Sean2
    Genius 3630 points

    Hi Sean,


    Thanks for your understanding of what I want exactly.

    I will try this first.

    Thanks a lot again,

    Ji Won