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I'm testing some software on NetBSD 8.1 x86_64. The software opens a USB modem and issues AT commands. The software tested OK on Debian, Fedora, OS X, and OpenBSD. The software is having trouble on NetBSD.

NetBSD's dmesg shows:

umodem0 at uhub1 port 1 configuration 2 interface 0
umodem0: U.S.Robotics (0xbaf) USB Modem (0x303), rev 2.00/2.00, addr 2, iclass 2/2
umodem0: data interface 1, has CM over data, has break
umodem0: status change notification available
ucom0 at umodem0

If I am parsing the NetBSD man pages properly (which may not be the case), I should be able to access the modem via /dev/ucom0. Also see UMODEM(4) man page.

The test user is part of the dialer group. The software was not able to open /dev/ucom0, /dev/umodem0, ucom0 or umodem0. All open's result in No such file or directory. Additionally, there are no /dev/ttyACMn or /dev/cuaUn devices.

How do I access the modem on NetBSD?

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How do I access the modem on NetBSD?

According to the NetBSD folks at Trouble accessing USB modems on NetBSD 8.1 x86_64:

  • The USR modem was assigned /dev/dtyU0. After a reboot I was able to access the modem through the device.

  • The Conexant modem with a CX93001 chip is a software modem. It uses a proprietary protocol from the chip to the driver. NetBSD does not have a driver for it, so it was assigned a ugen0. It can be accessed from /dev/ugen0.00, but it is not a tty device.

So to wrap this up for the BSDs, here are the devices to use to access a USB modem when things work as expected:

  • DragonFly - /dev/cuaU0
  • FreeBSD - /dev/cuaU0
  • NetBSD - /dev/dtyU0
  • OpenBSD - /dev/cuaU0
  • OS X - /dev/cu.usbmodem0000001

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