techblog

Line disciplines have been in Unix since a long time.  While they are not device drivers, they interact with tty devices in a very peculiar manner:  They attach to a tty device and can then look at, or manipulate, the data as it flows through the tty device.  Line disciplines are thus the natural choice when serial data is used in the kernel, e.g. to exchange TCP/IP packets over a serial link using the SLIP protocol or decoding date and time information and provide a timedelta sensor.

A while ago, Maurice Janssen (maurice@z74.net) sent me a modification of the nmea(4) line discipline to support the Meinberg Standard Time String format. With only a few changes, nmea(4) was turned into the msts(4) line discipline to support Meinberg's serial data format that can be emitted by all their radio clocks. I modified the code a bit, added a manual page, and added the bits needed to attach msts(4) to a tty to the ldattach(8) command. The result is that OpenBSD now has support for virtually any Meinberg radio-clock ever built.

I am currently writing a control and monitoring software system that makes use of GPIO pins. Since I was at the CCC congress in Berlin I did only have my laptop and no real GPIO hardware... With only a laptop it's a bit hard to write GPIO software, since laptops usually don't have any GPIO pins. So what I needed to test my new software was either a real device (out of reach) or... writing a simulator.

Marc Balmer , The OpenBSD Project Copyright (C) 2006 Marc Balmer Every computer is equipped with at least a clock chip or a general purpose device to provide a timer function. While these timers are certainly precise enough for measuring relatively short periods of time, they are not well suited for keeping the correct time and date over a longer period, since almost every chip drifts by a few seconds per day. Even so called real-time clocks only approximately meet the real time. Time signal stations can be a solution to this problem as they emit very precise time information using specifically modulated radio frequencies. Time signal stations are available in many countries; while the coding schemes vary from time signal station to time signal station, the decoding principles are similar.