Communicating with a FTDI device

[Jeffrey Walton]

Hi Everyone,

I purchased a OBDLink SX
(https://www.amazon.com/gp/product/B005ZWM0R4). The device uses a FTDI
chip. I'm having trouble communicating with it. Commands like ATZ\r
hang. I've tried using raw terminals (cfmakeraw) and existing
terminals (tcgetattr).

Here's what I see in the logs:

[ 1965.676799] traps: process-mbox-re[4668] general protection fault
ip:7fb027b65870 sp:7ffcb7640940 error:0 in
libc-2.31.so[7fb027aed000+178000]
[19699.167543] usb 1-14.1.3: new full-speed USB device number 14 using xhci_hcd
[19699.289442] usb 1-14.1.3: New USB device found, idVendor=0403,
idProduct=6015, bcdDevice=10.00
[19699.289448] usb 1-14.1.3: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[19699.289451] usb 1-14.1.3: Product: OBDLink SX
[19699.289455] usb 1-14.1.3: Manufacturer: ScanTool.net LLC
[19699.289457] usb 1-14.1.3: SerialNumber: 113011099400
[19699.300623] ftdi_sio 1-14.1.3:1.0: FTDI USB Serial Device converter detected
[19699.300686] usb 1-14.1.3: Detected FT-X
[19699.301830] usb 1-14.1.3: FTDI USB Serial Device converter now
attached to ttyUSB0

I'm beginning to wonder if I have a driver issue. I found a document
https://www.ftdichip.com/Support/Documents/AppNotes/AN_220_FTDI_Drivers_Installation_Guide_for_Linux.pdf.
The document is confusing me. It says the FTDI chip needs VCP driver
support to get a device assigned like /dev/ttyUSB0. But then it says
to unload the VCP related drivers (ftdi_sio and usbserial).

Here is what lsmod is telling me:

$ lsmod | grep -i -E 'usbserial|ftdi|d2'
ftdi_sio               61440  0
usbserial              53248  2 ftdi_sio,ch341

I'm currently using Ubuntu's 5.4.0-80 kernel. But I would also like to
use Fedora's 5.13.5-200 kernel.

My question is, what should we be doing to communicate with a FTDI
converter? What driver do we need nowadays?

Thanks in advance.