Hi
I have a few CH340/341 USB RS485 adapters - they all look identical
and use the ch341 driver with ID 1a86:7523 but I've found one that
reports a different iProduct and bcdDevice from the others. They all
work fine in Windows but one has problems transmitting in Linux.
I have tried this on a few different machines/kernels.
5.13.0-30-generic #33~20.04.1-Ubuntu SMP Mon Feb 7 14:25:10 UTC 2022 x86_64
5.10.92-v7+ #1514 SMP Mon Jan 17 17:36:39 GMT 2022 armv7l
5.10.93.2-microsoft-standard-WSL2 #2 SMP Sat Mar 5 13:40:04 PST 2022 x86_64
miniterm and dmesg offer some clues - the problem device shows
different CTS/DSR states
I have not been able to work around this with stty or in miniterm
problem device
miniterm
--- RTS: active DTR: active BREAK: inactive
--- CTS: inactive DSR: inactive RI: inactive CD: inactive
--- software flow control: inactive
--- hardware flow control: inactive
In Windows the Termite com program shows CTS/DSR/RI/CD active
If I run socat in Windows sharing the serial port, and socat Linux
using a pty the Linux serial application works perfectly but fails
using the ch341 driver directly
dmesg
[702953.276954] usb 3-4: new full-speed USB device number 2 using xhci_hcd
[702953.426006] usb 3-4: New USB device found, idVendor=1a86,
idProduct=7523, bcdDevice= 2.63
[702953.426014] usb 3-4: New USB device strings: Mfr=0, Product=2,
SerialNumber=0
[702953.426017] usb 3-4: Product: USB2.0-Serial
[702953.426919] ch341 3-4:1.0: ch341-uart converter detected
[702953.427336] usb 3-4: ch341-uart converter now attached to ttyUSB1
working device
miniterm
--- RTS: active DTR: active BREAK: inactive
--- CTS: active DSR: active RI: active CD: active
--- software flow control: inactive
--- hardware flow control: inactive
dmesg
[ 699.616711] usb 1-1.4: new full-speed USB device number 7 using ehci-pci
[ 699.726105] usb 1-1.4: New USB device found, idVendor=1a86,
idProduct=7523, bcdDevice= 2.54
[ 699.726113] usb 1-1.4: New USB device strings: Mfr=0, Product=2,
SerialNumber=0
[ 699.726117] usb 1-1.4: Product: USB2.0-Ser!
[ 699.726517] ch341 1-1.4:1.0: ch341-uart converter detected
[ 699.727292] ch341-uart ttyUSB0: break control not supported, using
simulated break
[ 699.727411] usb 1-1.4: ch341-uart converter now attached to ttyUSB0
lsusb - same vendor id
Bus 001 Device 007: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
Bus 003 Device 002: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
lsusb -v
The only difference is in bcdDevice, iProduct and MaxPower
problem device
Bus 003 Device 002: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 255 Vendor Specific Class
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 8
idVendor 0x1a86 QinHeng Electronics
idProduct 0x7523 HL-340 USB-Serial adapter
bcdDevice 2.63
iManufacturer 0
iProduct 2 USB2.0-Serial
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0027
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 98mA
working device
Bus 001 Device 007: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 255 Vendor Specific Class
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 8
idVendor 0x1a86 QinHeng Electronics
idProduct 0x7523 HL-340 USB-Serial adapter
bcdDevice 2.54
iManufacturer 0
iProduct 2 USB2.0-Ser!
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0027
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 96mA
