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Linux/AM5728: Changing UART3 baud rate in U-boot

David Tan21
Prodigy 120 points
Part Number: AM5728


Tool/software: Linux

How would one go about changing the UART3's baud rate from 115200 to 9600?

I believe I see a file in uboot/include/configs/dra7xx_evm.h, but are there anywhere else to change it? 

  • 0
    TI__Guru 55345 points

    Hello David,

    Please, apply this patch to change the baud rate to 9600.

    cd <Processor SDK>/board-support/u-boot-<version>/
    git apply 0001-AM57xx-Change-baud-rate-to-9600.patch

    Best regards,
    Kemal

  • 0 in reply to Kemal R. Shakir
    Prodigy 120 points

    Hey Kemal,

    Thanks for the quick response! I've applied the changes to a custom chip and the baud rate is a bit off.

    Originally the baud rate was set to 115200, and I was getting around 128000 measured with an oscilloscope. I wanted to see if a change to a lower baud rate would fix the problem, but it looks like it didn't! 

    I've checked the external crystals with an oscilloscope and the clocks are fine. We have a 20Mhz crystal for XO_OSC1 and XI_OSC1 and 22.5792Mhz for XI_OSC0 and XO_OSC0. 

    The weird part is that we have a first iteration custom chip made, and the baud rate is correct at 115200. The latest revision of the boards with the same layout and schematic doesn't work. Furthermore, I have an SD card with the same kernel and uboot, and the baud rate works well with the previous iteration, but not with the latest revision.

    My question is, what hardware or software checks can we perform further to determine the root cause of this issue? 

  • 0 in reply to David Tan21
    TI__Guru**** 393215 points

    Hi David,

    David Tan21 said:
    We have a 20Mhz crystal for XO_OSC1 and XI_OSC1 and 22.5792Mhz for XI_OSC0 and XO_OSC0. 

    You seem to have placed the crystals wrong. The 20MHz crystal should be on OSC0, which is the main oscillator, and 22.5792MHz should be on OSC1.

  • 0 in reply to Biser Gatchev-XID
    Prodigy 120 points

    Hey Biser, 

    Thanks so much for the help! It turns this was the solution! :)