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PRU Cape on BeagleBone Black

Chris Pendleton
Intellectual 410 points

Hello. I am having a problem running the PRU Cape Demo application on the BBB. I followed the instructions at: http://processors.wiki.ti.com/index.php/PRU_Cape_Getting_Started_Guide.


The problem is that I see nothing on the debug serial port via the FTDI cable when the PRU cape is attached to the BBB. It appears to work without the PRU cape attached - I do see the expected console output from the debug serial port when I remove the cape. I have seen the same result with 2 BBBs - one Rev B and one Rev C.

I also have a BeagleBone White (BBW). The PRU Cape and demo application work as expected with this device. A major difference here is that the FTDI chip is built into the BBW.

I notice that the PRU Cape LED power up sequence on the working BBW configuration is very different than the non-working BBB one. The BBB-PRU Cape combo only lights up D5,D6,D7 when power is applied.

Any help is appreciated.


Regards,

Chris

  • 0
    TI__Guru**** 393215 points

    Hi Chris,

    The wiki seems to be incorrect. BBB does not have an FTDI chip onboard. Instead you will need to connect a serial level translator to the pin header J1. BBB schematics can be found at: http://elinux.org/Beagleboard:BeagleBoneBlack#Hardware_Files

  • 0 in reply to Biser Gatchev-XID
    Intellectual 410 points

    Hi Biser. Thanks for the reply.


    I do not think the wiki is incorrect. It says required: "FTDI cable for BeagleBone Black serial debug port (not required for original BeagleBone)" and "3. Plug the FTDI cable into your host PC and connect to the BeagleBone Black." I know about this FTDI cable and it is connected to J1. It works fine when running Linux or Starterware apps. It just doesn't produce any output when the PRU Cape is attached. I do not think there is any problem with the FTDI cable, or the serial debug function. I suspect it is a hardware/power/boot problem, based on the lack of LED activity when power is applied.

    The PRU Cape hardware does work when paired with the BBW. This coupled with the fact that I saw the same behavior on 2 separate BBB units leaves me scratching my head. I must be missing something. I know this product is very new, but TI must have tested this with BBBs...

    Regards,

    Chris

  • 0 in reply to Chris Pendleton
    TI__Genius 15920 points

    Hi Chris,

    Yes, the PRU Cape has been extensively tested with the BBB.  

    Are you using the BBB specific MLO when preparing your SD card?  Note that the BBB and BBW use different MLOs.  The BBB MLO can be found in the pru_cape/bin/MLO/beaglebone_black directory of the PRU Software Support Package.  

    Regards,

    Melissa

  • 0 in reply to melissaw
    Intellectual 410 points

    Hi Melissa.


    Thank you very much for your response.


    Yes, I am using the BBB-specific MLO. I am currently running the demo programs on the BBB without the cape and looking at the output signals with a scope. I am able to see the expected square wave for the LED blink demo. When I attach the cape I see the problems described earlier.

    I would like to blame the cape unit, but it works perfectly with the BBW. So I am still scratching my head...

    Thanks,
    Chris

  • 0 in reply to Chris Pendleton
    TI__Genius 15920 points
    Hi Chris,

    Using CCS, are you able to connect to the ARM and read the control_status register (0x44E10040)? I suspect that the boot order is somehow being changed on the BBB. We expect control_status[5:0] to be either "11100" or "11000."

    Regards,
    Melissa