RB5 UART for external FC not working.

  • Hi, We have been trying to connect the two external UARTS to read/write mavlink and micrortps to an external FC.

    J12 - /dev/ttyHS1
    J19 - /dev/ttyHS2

    On the RB5 EVT the software works with the embedded flight controller. However on the RB5 flight deck it does not. To further test we found that using an FTDI adapter, we see no transmission communication from the RB5. We also found that it is unable to read data on the RX pin either.

    Another test we did was to run the following software:

    import serial
    uart = serial.Serial(uart_dev, 57600, xonxoff=False, rtscts=False, dsrdtr=False)
    while True:
        for b in bytearray("message\n","UTF-8"):
        line = uart.read_all()
        if(len(line) > 0):

    We connected an oscilloscope and tried measuring the TX signal in reference to ground. We observed no changes in the signal.

    I noticed the documentation has been removed from the main RB5 guide documents. Is this a known issue/ is there a way to resolve it (perhaps using a different driver). It would be really nice to be able to use those UARTS.

    Thank you for the help.

  • Dev Team

    Hi @mrawding ,

    You are correct, there's something wrong, and I'm investigating this now.

    The UART is active after bootup but then something fishy is happening.

    When used with PX4 (ran on bootup) there's no issue.

    I'll post here when there's an update to fix.

  • Hi @modaltb any updates on this issue yet ?

  • Dev Team

    @mrawding yes, we have a fix that will be in the next SDK download, but I'll send an email to the one on this account now and share a link.

    The issue was tricky to figure out, but when PX4 is not running on the DSP, sensor power rails were being disabled that powered off the UARTs!

  • Hi @modaltb. Could you please share the updated SDK or System Image that contains this fix?

  • @modaltb hello, when will the next SDK release be available? Would love to the UARTs working for external FC. Thank you.