Bad USB behavior with FTDI device

Plugging in an FTDI-based serial to USB converter device, Rocky 9.2 and 9.3 exhibit the same behaviors, making it impossible to run minitab or other serial terminal using the converter.

Once data starts flowing from the external device… both the system log and dmesg report /dev/ttyUSB0 being created, being destroyed, then /dev/ttyUSB1 being created and destroyed. Then back to /dev/ttyUSB0 etc. Executing /dev/ttyUSB* over and over you can see the system bouncing back and forth between the two devices. First only ttyUSB0 exists. Then only ttyUSB1 exists. Then back again. The cycle takes about 3-4 seconds.

If you stop sending serial data to the computer, then the ttyUSB0/ttyUSB1 bouncing stops. If you resume sending serial data, it starts up again.

This instruction sheet from ftdichip.com suggests executing:

sudo rmmod ftdi_sio
sudo rmmod usbserial

The first command reports no errors, but the second command reports “ERROR: Module usbserial is builtin”. The net effect of both commands is no change.

Even after ‘rmmod ftdi_sio’, the system log continues to report messages from ftdi_sio, so it appears that the command has no effect.

The same device works fine with Ubuntu 18.04.

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A section of the syslog is:
S111 kernel: usb 1-2: new full-speed USB device number 70 using xhci_hcd
S111 kernel: usb 1-2: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
S111 kernel: usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
S111 kernel: usb 1-2: Product: FT232R USB UART
S111 kernel: usb 1-2: Manufacturer: FTDI
S111 kernel: usb 1-2: SerialNumber: B0010TRK
S111 kernel: ftdi_sio 1-2:1.0: FTDI USB Serial Device converter detected
S111 kernel: usb 1-2: Detected FT232R
S111 kernel: usb 1-2: FTDI USB Serial Device converter now attached to ttyUSB0
S111 kernel: usb 1-8: USB disconnect, device number 69
S111 kernel: ftdi_sio ttyUSB1: FTDI USB Serial Device converter now disconnected from ttyUSB1
S111 kernel: ftdi_sio 1-8:1.0: device disconnected
S111 upowerd[1544]: treating change event as add on /sys/devices/pci0000:00/0000:00:02.1/0000:03:00.0/0000:04:0c.0/0000:0e:00.0/usb1/1-2
S111 kernel: usb 1-8: new full-speed USB device number 71 using xhci_hcd
S111 kernel: usb 1-8: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
S111 kernel: usb 1-8: New USB device strings: Mfr=1, Product=2, SerialNumber=3
S111 kernel: usb 1-8: Product: FT232R USB UART
S111 kernel: usb 1-8: Manufacturer: FTDI
S111 kernel: usb 1-8: SerialNumber: B0010TRK
S111 kernel: ftdi_sio 1-8:1.0: FTDI USB Serial Device converter detected
S111 kernel: usb 1-8: Detected FT232R
S111 kernel: usb 1-8: FTDI USB Serial Device converter now attached to ttyUSB1
S111 kernel: usb 1-2: USB disconnect, device number 70
S111 kernel: ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
S111 kernel: ftdi_sio 1-2:1.0: device disconnected
S111 upowerd[1544]: treating change event as add on /sys/devices/pci0000:00/0000:00:02.1/0000:03:00.0/0000:04:0c.0/0000:0e:00.0/usb1/1-8
S111 kernel: usb 1-2: new full-speed USB device number 72 using xhci_hcd
S111 kernel: usb 1-2: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
S111 kernel: usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
S111 kernel: usb 1-2: Product: FT232R USB UART
S111 kernel: usb 1-2: Manufacturer: FTDI
S111 kernel: usb 1-2: SerialNumber: B0010TRK
S111 kernel: usb 1-2: FTDI USB Serial Device converter now attached to ttyUSB0
S111 kernel: usb 1-8: USB disconnect, device number 71
S111 kernel: ftdi_sio ttyUSB1: FTDI USB Serial Device converter now disconnected from ttyUSB1
S111 kernel: ftdi_sio 1-8:1.0: device disconnectedS111 upowerd[1544]: treating change event as add on /sys/devices/pci0000:00/0000:00:02.1/0000:03:00.0/0000:04:0c.0/0000:0e:00.0/usb1/1-2
S111 kernel: usb 1-8: new full-speed USB device number 73 using xhci_hcd
S111 kernel: usb 1-8: New USB device found, idVendor=0403, idProduct=6001, bcdDevice= 6.00
S111 kernel: usb 1-8: New USB device strings: Mfr=1, Product=2, SerialNumber=3
S111 kernel: usb 1-8: Product: FT232R USB UART
S111 kernel: usb 1-8: Manufacturer: FTDI
S111 kernel: usb 1-8: SerialNumber: B0010TRK
S111 kernel: ftdi_sio 1-8:1.0: FTDI USB Serial Device converter detected
S111 kernel: usb 1-8: Detected FT232R
S111 kernel: usb 1-8: FTDI USB Serial Device converter now attached to ttyUSB1
S111 kernel: usb 1-2: USB disconnect, device number 72
S111 kernel: ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
S111 kernel: ftdi_sio 1-2:1.0: device disconnected
S111 upowerd[1544]: treating change event as add on /sys/devices/pci0000:00/0000:00:02.1/0000:03:00.0/0000:04:0c.0/0000:0e:00.0/usb1/1-8
S111 kernel: usb 1-2: new full-speed USB device number 74 using xhci_hcd
S111 kernel: usb 1-8: USB disconnect, device number 73
S111 kernel: ftdi_sio ttyUSB1: FTDI USB Serial Device converter now disconnected from ttyUSB1
S111 kernel: ftdi_sio 1-8:1.0: device disconnected

You could try with a newer kernel provided by elrepo: start [ELRepo Wiki]

There is kernel-lt and kernel-ml which are 6.x kernels.

I also tried the suggestion of
https://forums.linuxmint.com/viewtopic.php?t=362743

to execute the commands
modprobe ftdi_sio
echo 0403 6001 >/sys/bus/usb-serial/drivers/ftdi_sio/new_id

That accomplished nothing. New device found/disconnect cyclical behavior continues unabated.

Another suggestion is to remove brltty. That was not installed but I also removed blrapi and all its apis. No change.

For what it is worth, the device number cycles from 9, 10, 11, 12,… to 127 over and over again.

Also: disabling upower had no effect except to remove the upower messages from the system log.