Rachie Rachie - 3 months ago 14
Linux Question

Cygnal Integrated Products serial port on Linux

I have an infrared thermometer which operates on a virtual serial port over USB, which I am trying to use on Debian Linux. Unfortunately, the system does not enumerate a

/dev/ttyUSB
device.

Here is the
dmesg
for the device:

usb 5-1: new full-speed USB device number 3 using uhci_hcd
usb 5-1: New USB device found, idVendor=10c4, idProduct=834b
usb 5-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 5-1: Product: Infrared Online Sensor Adapter
usb 5-1: Manufacturer: Silicon Labs
usb 5-1: SerialNumber: CT00092755


And here is the
lsusb -v
:

Bus 005 Device 003: ID 10c4:834b Cygnal Integrated Products, Inc.
Couldn't open device, some information will be missing
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x10c4 Cygnal Integrated Products, Inc.
idProduct 0x834b
bcdDevice 1.00
iManufacturer 1
iProduct 2
iSerial 3
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 32
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 255 Vendor Specific Class
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 2
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0


How can I get this working, so I can connect to it with the serial port?

Answer

It turns out this devices uses a standard Silicon Labs CP2102 interface chip, which the device manufacturer loaded with a custom idProduct number. While the chip is 100% compatible with the cp210x.ko driver, the idProduct is not recognized by the system, and does not associate the driver with it.

At this point, there are several possible solutions:

  • Manually direct the system to use the cp210x.ko driver with this idProduct.
  • Add the idProduct to the open source driver, compile, and install it. Then try to push the changes into standard Linux repositories.
  • Replace the customized chip with generic one.
  • Rewrite the idProduct on the chip.

I chose to rewrite the idProduct. Silicon Labs has a free utility to do just this. I set the idProduct=EA60, which is the default for this chip. The device is now recognized by the standard built-in driver, and works perfectly.