Linux USB Driver message to Jrk 21v3

I’m am trying to control two linear actuators with two Jrk 21v3 boards. I have a problem with one, that doesn’t happen on the other and I’ve run out of ideas for what is wrong.

I am connecting both over USB, if I connect them using my Windows machine, the Jrk Configuration Utility has no issues finding both devices. However, the final project is done on a Linux machine. Both of them are enumerated as /dev/ttyACM0 through /dev/ttyACM3 correctly, but my code only is able to communicate with one of them.

I also tried the JrkCmd utility to see if it was my code. For one, ./JrkCmd -l lists the device number, but for the other I get an error message:
“Error: Error getting serial number string from device (pid=83, vid=1ffb).
I/O error.”

I noticed that on the one that doesn’t work correctly, the green LED blinks rapidly as soon as it is connected, and then starts to blink slowly, while on the other board it is solid the whole time. The User Guide says that:
"When you connect the jrk to USB, the green LED will start blinking slowly. The blinking continues until the jrk receives a particular message from the computer indicating that the jrk’s USB drivers are installed correctly"
Is there a way I can force this “message” from my computer, or some other solution and/or workaround?

The Windows utility doesn’t show any other errors from the usual “awaiting command” and "no power"
I’ve also successfully sent and received commands to the boards via the Pololu Serial Transmitter program in Windows, so it seems to be an issue with the host machine.

uname -a on Ubuntu 14.04 linux shows:
Linux Orion 3.13.0-24-generic #47-Ubuntu SMP Fri May 2 23:30:00 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

Any information on why one would work but not the other would be appreciated. Let me know if I can provide any more information that would help.


I am sorry you are having trouble with one of your jrk 21v3 motor controllers. If you haven’t already, could you try the following? Please try disconnecting everything from both of the jrks. Then plug the working one into USB and confirm that the green LED is on solid and “JrkCmd -l” shows it. Then replace the working one with the other one and see what results you get. The goal of this is to see if the jrks behave differently even when they are in the exact same setup, using the same USB port and cable. If you are using an external USB hub, could you also try connecting the jrks directly to the Linux machine instead?

For the jrk that isn’t working, could you plug it in and then post the output from “dmesg” that corresponds to it? There should be messages about Linux detecting a new USB device and activating the cdcacm driver.

Since the jrk is doing a slow green blink while the computer shows virtual serial ports for it, it seems that the jrk and the computer have gotten out of sync and they disagree about what state the jrk is in.

I am not sure why you are seeing fast blinking of the green LED at startup.