Monday, November 23, 2015

Using ser2net for serial access.

Is your table a mess of wires? Do you have multiple devices connected via serial and can't remember which is /dev/ttyUSBX is connected to what board? Unless you are a embedded developer, you are unlikely to deal with serial much anymore - In that case you can just jump to the next post in your news feed.

Introducting ser2net

Usually people start with minicom for serial access. There are better tools - picocom, screen, etc. But to easily map multiple serial ports, use ser2net. Ser2net makes serial ports available over telnet.

Persistent usb device names and ser2net

To remember which usb-serial adapter is connected to what, we use the /dev/serial tree created by udev, in /etc/ser2net.conf:
# arndale
7004:telnet:0:'/dev/serial/by-path/pci-0000:00:1d.0-usb-0:1.8.1:1.0-port0':115200 8DATABITS NONE 1STOPBIT
# cubox
7005:telnet:0:/dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller_D-if00-port0:115200 8DATABITS NONE 1STOPBIT
# sonic-screwdriver
7006:telnet:0:/dev/serial/by-id/usb-FTDI_FT230X_96Boards_Console_DAZ0KA02-if00-port0:115200 8DATABITS NONE 1STOPBIT
The by-path syntax is needed, if you have many identical usb-to-serial adapters. In that case a Patch from BTS is needed to support quoting in serial path. Ser2net doesn't seems very actively maintained upstream - a sure sign that project is stagnant is a homepage still at sourceforge.net... This patch among other interesting features can be also be found in various ser2net forks in github.

Setting easy to remember names

Finally, unless you want to memorize the port numbers, set TCP port to name mappings in /etc/services:
# Local services
arndale            7004/tcp
cubox              7005/tcp
sonic-screwdriver  7006/tcp
Now finally:
telnet localhost sonic-screwdriver
^Mandatory picture of serial port connection in action
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