Dr. Lawlor's Code, Robots, & Things

February 27, 2014

Ubuntu USB serial circuit boards vs “modem-man”

Filed under: Arduino, Hardware, Linux — Dr. Lawlor @ 9:41 pm

For CYBER-Alaska we built a custom Arduino-style circuit board (“Rovoduino”) that connects to the PC via USB.  It generally worked, but there was always a weird half-minute delay when you plugged it into a Linux PC before anything would start to work.  Tonight I was testing a new sensor on an Arduino Mega, a similar board, and noticed the plug-in-to-work delay there was only a little over one *second* (due to the bootloader).

Back to my custom board, trying a “sudo lsof | grep ttyUSB” during the half-minute delay shows the unexpected process “modem-man” spending this time sending commands like “AT+++” and trying to convince my circuit board that it is, in fact, a modem.

It’s not a modem.

You can explicitly blacklist your custom USB device from modem-man on Ubuntu in /lib/udev/rules.d/77-mm-usb-device-blacklist.rules, but it’s more reliable to just remove the darn thing entirely:

sudo apt-get remove modemmanager

Because seriously, who uses a modem?

This makes plugging and working on my USB serial board a lot snappier!

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