I have an imx6 embedded board which is connected through FTDI/USB to a linux host. The embedded board runs a Yocto linux. I send commands to the embedded board through a serial interface (ie. write to the USB device /dev/ttyUSB0). The Linux on the embedded board runs in its RAM, with NFS file system.

I have been observing the following behaviour. After a few commands over the serial communication, I get the following error on the target:

<..>USB modem converter now disconnected from USB0
qcserial: 2-1.1:1.0 device disconnected
usb 2-1.1: config 1 has an invalid interface number: 8 but max is 3
usb 2-1.1:config 1 has no interface number 1

Also, the error on the host is:

[ 5015.112569] usb usb1-port2: disabled by hub (EMI?), re-enabling...
[ 5015.112578] usb 1-2: USB disconnect, device number 2
[ 5015.112955] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[ 5015.112975] ftdi_sio 1-2:1.0: device disconnected
[ 5015.383005] usb 1-2: new high-speed USB device number 6 using xhci_hcd
[ 5015.531596] usb 1-2: New USB device found, idVendor=0403, idProduct=6011
[ 5015.531599] usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 5015.531601] usb 1-2: Product: Quad RS232-HS
[ 5015.531603] usb 1-2: Manufacturer: FTDI
[ 5015.532206] ftdi_sio 1-2:1.0: FTDI USB Serial Device converter detected
[ 5015.532247] usb 1-2: Detected FT4232H
[ 5015.532381] usb 1-2: FTDI USB Serial Device converter now attached to ttyUSB4

Now the undesired effect is also that ttyUSB0 is now ttyUSB4, which causes my program to crash.

Could someone give me some suggestions to fix this issue please?


1 Answer 1


Troubleshooting process is rather simple: you must find the device causing it. Try another cable, try another USB port in the linux host, try another intermediate device (USB hub) if there's any. Finally, try another embedded board. As soon as you find the cause, focus on fixing/replacing the faulty component.


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