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how does booting from uart0 exactly work

ronny suy
Prodigy 120 points

Hi

I wan't to know how booting from uart0 exacly works. I have a BBB and when I press the S2 button then I see 'C' chars printed on my terminal.

Does this mean its waiting for an x-modem file or is this a time out from the watchdog? Because in the datasheet is mentioned that the rom code polls the host 10times in 3 seconds. Does this mean I have to upload an x-modem file in this 3 second period ? I'm confused by this , because you have to be very fast in typing to do this ...;-)

Hoping someone can help me on this,

Kind regards

Ronny

  • 0
    TI__Mastermind 25235 points

    Hi Ronny,

    The "C" characters are printed when the board is waiting for the u-boot-spl.bin file to be sent via UART.

    The time before the board tries the next boot source is indeed 3 seconds. Currently I don't have a BeagleBone Black with me, but the correct procedure to send the u-boot-spl.bin file via UART should be:

    1. The board is switched off.
    2. Send the file via X-Modem.
    3. Start the board and initiate UART booting.
    4. After the transfer is complete, the board will be waiting for u-boot.img file. Send it.
    5. The board will boot in U-Boot.

    P.S. If you want to remove the 3 seconds limitation before the ROM code switches to another boot source just remove all other boot sources (like SD card). In this case, the board will try again and again to boot from UART and you can initiate the transfer within a longer period after the board has been switched on.

    Please note that there is another timing constraint:

    Once the transfer has started, if the host does not send any packet for 3s, UART boot will time out

    This means that once you initiate the file transfer, you have 3 seconds to send the first packet (to type the path to the file). What you can do is just copy->paste the path instead of typing it.

    Best regards,
    Miroslav

  • 0 in reply to Miroslav Kiradzhiyski XID
    Prodigy 230 points
    Miroslav,

    After SPL has been downloaded via X-Modem, there is a pretty long delay before the Y-Modem transfer starts and another pretty long delay after the Y-Modem transfer (of u-boot.img) completes, before u-boot starts and you get a u-boot prompt. By pretty long I mean on the order of a minute.

    Do you know what causes this delay and what one can do to eliminate it?

    Best Regards,
    Paul