Activating a USB modem after Big Sur restart

I have a USB modem that worked fine under Mojave. With Big Sur (11.2.3), the device is not recognized immediately after a restart (/dev/cu.usbmodem123456781 does not exist). However, if I unplug the device and then replug into the USB port, /dev/cu.usbmodem123456781 exists and can be used. I'm accessing the device programmatically in a macOS app, using Objective-C.

After a restart, System Report correctly lists the USB modem (even before unplug/replug) as follows:

USB Modem:
  Product ID: 0x1340
  Vendor ID: 0x0572 (Conexant Systems, Inc.)
  Version: 1.00
  Serial Number: 12345678
  Speed: Up to 12 Mb/s
  Manufacturer: Conexant
  Location ID: 0x14110000 / 5
  Current Available (mA): 500
  Extra Operating Current (mA): 0

What can I do so that /dev/cu.usbmodem123456781 exists after a restart?
Up vote post of Jeff_m Down vote post of Jeff_m
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Jeff_m
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  • Hi Jeff,

    If you have something ready in accordance with what I need, I can pay for it!

    Thanks.

    —
    CaduRJ
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Hi Jeff!

I need to develop an objective-C app in order to access a USB modem via cable for activation.

Could you please tell me the best way to start? Do you have something you could share?

Thanks in advance!

Posted by
CaduRJ
Up vote reply of CaduRJ Down vote reply of CaduRJ

  • Sorry for the delay. I just now saw your request. In case you are still interested, here's my sequence. I use the sharedSerialPortManager to loop through the serial ports, looking for a port description that includes the string "usbmodem". When found, I create the path as "/dev/cu." plus the full modem description (e.g., "/dev/cu.usbmodem123456781") then I open that path using ORSSerialPort serialPortWithPath:. I send the string "ATE0+VCID=1" to the moden serial port using sendData: and process the responses using the ORSSerialPortDelegate method didReceiveData:.

    —
    Jeff_m
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