EC25 ttyUSB number

Technical Subjects
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1

i have two devices with EC25 that use the same fireware, but the number of /dev/ttyUSB* is different.

one is /dev/ttyUSB3  /dev/ttyUSB4  /dev/ttyUSB5  /dev/ttyUSB6  /dev/ttyUSB7
[   12.355293] usb 1-1.1: new high-speed USB device number 4 using xhci-mtk
[   12.473847] option 1-1.1:1.0: GSM modem (1-port) converter detected
[   12.480473] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB3
[   12.487975] option 1-1.1:1.1: GSM modem (1-port) converter detected
[   12.494573] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB4
[   12.502156] option 1-1.1:1.2: GSM modem (1-port) converter detected
[   12.508691] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB5
[   12.516317] option 1-1.1:1.3: GSM modem (1-port) converter detected
[   12.522893] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB6
[   12.530465] option 1-1.1:1.4: GSM modem (1-port) converter detected
[   12.537087] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB7

and the another is /dev/ttyUSB3  /dev/ttyUSB4  /dev/ttyUSB5  /dev/ttyUSB6
[   22.398487] usb 1-1.1: USB disconnect, device number 4
[   22.404209] option1 ttyUSB3: GSM modem (1-port) converter now disconnected from ttyUSB3
[   22.412398] option 1-1.1:1.0: device disconnected
[   22.417741] option1 ttyUSB4: GSM modem (1-port) converter now disconnected from ttyUSB4
[   22.426094] option 1-1.1:1.1: device disconnected
[   22.431574] option1 ttyUSB5: GSM modem (1-port) converter now disconnected from ttyUSB5
[   22.439824] option 1-1.1:1.2: device disconnected
[   22.445053] option1 ttyUSB6: GSM modem (1-port) converter now disconnected from ttyUSB6
[   22.453353] option 1-1.1:1.3: device disconnected
[   22.458710] option1 ttyUSB7: GSM modem (1-port) converter now disconnected from ttyUSB7
[   22.467105] option 1-1.1:1.4: device disconnected
[   24.130187] usb 1-1.1: new high-speed USB device number 5 using xhci-mtk
[   24.262202] rndis_host 1-1.1:1.0 usb1: register 'rndis_host' at usb-1a1c0000.usb-1.1, RNDIS device, 9a:bf:48:45:54:77
[   24.274829] option 1-1.1:1.2: GSM modem (1-port) converter detected
[   24.281529] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB3
[   24.289123] option 1-1.1:1.3: GSM modem (1-port) converter detected
[   24.295799] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB4
[   24.303536] option 1-1.1:1.4: GSM modem (1-port) converter detected
[   24.310428] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB5
[   24.318100] option 1-1.1:1.5: GSM modem (1-port) converter detected
[   24.324840] usb 1-1.1: GSM modem (1-port) converter now attached to ttyUSB6

i want to know why there is such a different and how to ensure that the number of /dev/ttyUSB* is fixed

2

Generally speaking, start from ttyUSB0, unless there are other ttyUSBs on this device. It is difficult to fix in the kernel driver. I would recommend to use the udev.

SUBSYSTEMS==“usb”, ENV{.LOCAL_ifNum}=“$attr{bInterfaceNumber}”

SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0121", ENV{.LOCAL_ifNum}=="02", SYMLINK+="EC21.AT", MODE="0660"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0121", ENV{.LOCAL_ifNum}=="03", SYMLINK+="EC21.MODEM", MODE="0660"

SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0125", ENV{.LOCAL_ifNum}=="01", SYMLINK+="EC25.NMEA", MODE="0660"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0125", ENV{.LOCAL_ifNum}=="02", SYMLINK+="EC25.AT", MODE="0660"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB[0-9]*", ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0125", ENV{.LOCAL_ifNum}=="03", SYMLINK+="EC25.MODEM", MODE="0660"

The /dev/EC25.AT would automatically link to the AT port. And so the /dev/EC25,AT could be used to send the AT.