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AM4376: am437x: How to enable UART0 (debug serial) in u-boot-spl?

Takeshi Dodo
Prodigy 30 points

Part Number: AM4376

  • I'd like U-Boot SPL to output the following log messages to the serial console during startup. 
    • U-Boot SPL 2014.07-00001-g7612224-dirty (Feb 24 2026 - 19:35:39)
  • However, nothing is printed on UART0. 
    • SDK version: 11.02.05.02
    • using defconfig: am43xx_evm_defconfig
  • Even when I used the SDK's board-support/prebuilt-images/am437x/evm/MLO-am437x-evm, no log was output.
  • So I guess that UART0 is not enabled.
  • By the way, I'm sending U-Boot SPL to the board using Tera Term's XMODEM.
  • How should I customize the defconfig, device tree, or other settings so that the boot log is output on UART0?
  • 0
    TI__Expert 5960 points

    Hi Takeshi,

    Are you getting the initial "CCCC" from uart boot?

    Takeshi Dodo said:
    • By the way, I'm sending U-Boot SPL to the board using Tera Term's XMODEM.

    Are you sending u-boot.img with Y-modem after loading SPL with X-modem?

    The SPL will be expecting u-boot.img to be sent, and will not print the banner to not interrupt the oncoming Y-modem file transfer handshake.

    Please check if you are getting prints after loading u-boot.img.

    If not, can you decompile and share the device tree?

    Regards,
    Vinu

  • 0 in reply to Vinuchandran A V
    Prodigy 30 points

    Thanks for replying.

    Are you getting the initial "CCCC" from uart boot?
    > No.

    Are you sending u-boot.img with Y-modem after loading SPL with X-modem?
    > No. Y-modem is not working.

    If not, can you decompile and share the device tree?
    > I've attached the results of the commands below.

    　$ dtc -I dtb ti-processor-sdk-linux-am437x-evm-11.02.05.02/board-support/u-boot-build/arch/arm/dts/am437x-gp-evm.dtb > tmp.txt

    tmp.txt

  • 0 in reply to Takeshi Dodo
    Prodigy 30 points

    Hi, Vinu san.

    By doing the following two steps, only <debug_uart> is now output.

    ①Write u-boot-spl.bin instead of MLO.

    ②Add the following to am43xx_evm_defconfig.

    CONFIG_DEBUG_UART_BASE=0x44e09000
    CONFIG_DEBUG_UART_CLOCK=48000000
    CONFIG_DEBUG_UART=y
    CONFIG_DEBUG_UART_OMAP=y
    CONFIG_DEBUG_UART_SHIFT=2
    CONFIG_DEBUG_UART_ANNOUNCE=y

    CONFIG_SPL_BANNER_PRINT=y

    Regards,
    Takeshi.

  • 0 in reply to Takeshi Dodo
    TI__Expert 5960 points

    Hi Takeshi san,

    Glad to hear you are getting the required prints now.

    Do you need anymore support on this thread?

    Regards,
    Vinu

  • 0 in reply to Vinuchandran A V
    Prodigy 30 points

    Hi, Vinu san.

    Do you need anymore support on this thread?

    > Yes. Now, <debug_uart> is only output. But I want to know how to output the following log:

    • U-Boot SPL 2014.07-00001-g7612224-dirty (Feb 24 2026 - 19:35:39)


    Regards,
    Vinu

  • 0 in reply to Takeshi Dodo
    TI__Expert 5960 points

    Hi Takeshi san,

    I don't have a Windows machine handy now to try this out on Teraterm, I'll try to run this and get back to you next week.

    Meanwhile, by any chance, can you try the bootloaders without uart, may be with SD card, to ensure proper working?

    Regards,
    Vinu

  • 0 in reply to Vinuchandran A V
    TI__Expert 5960 points

    Hi Takeshi san,

    Apologies for the delayed response. 

    Takeshi Dodo said:
    Are you getting the initial "CCCC" from uart boot?

    I could get the CCCC and was able to send the bootloaders via uart and boot the board, with the prebuilt bootloaders.

    Can you make sure you are using the following SYSBOOT config?


    SYSBOOT[4:0] = 11001b

    Please let me know if you are getting CCC over uart terminal.

    Regards,
    Vinu

     

  • 0 in reply to Vinuchandran A V
    TI__Expert 5960 points

    Hi Takeshi san,

    I'm sharing the bootlogs from my side.

    I could see the U-boot SPL banner. 

    Note that I've used a Linux host machine with minicom serial terminal.

    Fullscreen bootlogs 2.txt Download 
    CCC                                                                                                                                          
U-Boot SPL 2025.01-00718-ga44465cad8a3 (Nov 14 2025 - 10:48:56 +0000)                                                                        
Trying to boot from UART                                                                                                                     
CCLoaded 828572 bytes                                                                                                                        
                                                                                                                                             
                                                                                                                                             
U-Boot 2025.01-00718-ga44465cad8a3 (Nov 14 2025 - 10:48:56 +0000)                                                                            
                                                                                                                                             
CPU  : AM437X-GP rev 1.2                                                                                                                     
Model: TI AM437x GP EVM                                                                                                                      
DRAM:  2 GiB                                                                                                                                 
Core:  37 devices, 18 uclasses, devicetree: separate                                                                                         
PMIC:  TPS65218                                                                                                                              
NAND:  512 MiB                                                                                                                               
MMC:   OMAP SD/MMC: 0                                                                                                                        
Loading Environment from FAT... MMC: no card present                                                                                         
** Bad device specification mmc 0 **                                                                                                         
Net:   eth2: ethernet@4a100000                                                                                                               
Hit any key to stop autoboot:  0                                                                                                             
=>

    Regards,
    Vinu