** This is a fork of radioclkd2 from http://www.jonatkins.com/page/software/radioclkd2
** originally written by Jon Atkins.

** Forked by Christian Vogel <vogelchr@vogel.cx> to add support for Linux
** GPIO pins in interrupt mode.

radioclkd2 - an interface between simple radio clock recievers and ntpd
-----------------------------------------------------------------------

This program will decode the time from simple MSF, DCF77 and WWVB recievers
and pass the time to ntpd via the SHM driver (28). These clocks just pass
the raw second pulses to the DCD, CTS, DSR or RNG serial line.


Hardware:

You need a MSF (UK), DCF77 (Germany/Europe) or WWVB (North America) receiver
which directly drives a serial line. The Swiss HGB uses a format (almost)
identical to DCF77 so should also work.

Want to build your own reciever? See Jonathan Buzzard's page
  http://www.buzzard.org.uk/jonathan/radioclock.html

TimeTools claim their clock outputs raw MSF, but I have not tested this.
  http://www.timetools.co.uk/


Installation:

To install:
  tar zxvf radioclkd2-X.YY.tar.gz
  cd radioclkd2-X.YY
  ./configure
  make
  make install

By default, radioclkd2 is installed to /usr/local/sbin/


Usage:

You need ntpd. Download source from http://www.ntp.org/

You need to enable SHM support in ntpd. This isn't enabled by default.
  ./configure --enable-SHM
now install ntpd
  make
  make install


To use this as a drop-in replacement for Jonathan Buzzard's radioclkd
use
 for 1 clock:  radioclkd2 ttyXX 
 for 2 clocks: radioclkd2 ttyXX ttyXX:cts

For more details, run radioclkd2 without parameters.


Bugs and Limitations:

radioclkd2 can operate in one of three modes:
* poll
 - should work on any Posix system
 - supports all 4 serial lines
 - least accurate - perhaps +-2ms at best
* iwait
 - Linux only - uses the TIOCMIWAIT ioctl
 - only supports DCD, CTS and DSR - RNG only triggers an interrupt one way
 - good accuracy - under +-1ms is possible, perhaps as good as +-0.2ms
* timepps
 - FreeBSD (and Linux with ppskit? - not tested)
 - only supports DCD - only 1 clock per serial port
 - good accuracy - at least as good as iwait
* gpio
 - Supports GPIO pins on Linux (e.g. on the Raspberry Pi)

History:

0.01
 Serial interface code done
 Decode of MSF complete

0.02
 Decode of DCF77 complete
 SHM code written
 timepps code written to support FreeBSD
 Added code to average the time offset from the last 60 seconds

0.03
 Decode of WWVB written but not tested
 Command line processing written
 Fixed DCF77 day-of-week check (it goes from 1 to 7, not 0 to 6)
 Changed the average code to filter out bad samples

0.04
 README written
 Removed hard-coded clock offsets - now a run-time option
 FIRST PUBLIC RELEASE

0.05
 Added missing #include <time.h> to decode_*.c
 Changed time offset limit on median filter to 100ms
 Added leap-second reporting for DCF77 and WWVB - not available in MSF

0.06
 Changed to use autoconf

0.07
 Fixed WWVB support. Existing MSF users will need to alter their startup
 scripts to include "-t msf".