POCSAG/DAPNET Support

[travisgoodspeed]

Use this issue to track development of a POCSAG receiver, intended for use on Dapnet at 439.9875 MHz.

Progress:

• Correct modulation, SYNC.
• Receiving frames.
• Decoding frames to recover meaningful text.
• Standalone applet.
• Power budget calculations.
• Preamble polling to sleep between transmissions.
• Checksum bit support.
• Long Packet Support (Long Packet Support #107)
• Error correction works.
• Documentation checked for accuracy in source code and wiki.

[travisgoodspeed]

Successfully decoding packets with some code that is far too ugly to commit! Next free weekend should see proper support in the main branch.

[travisgoodspeed]

The power situation is pretty dire: We spend 16mA while actively listening, exhausting the coin cell in only six hours! As a temporary solution, I'm exiting the pager app when no packets have been seen for three minutes. Later, we can match the transmitter's timeslot to sleep between packets, hopefully extending usage to more than a day.

[travisgoodspeed]

This module is still a work in progress, but documentation is up on the wiki.
https://github.com/travisgoodspeed/goodwatch/wiki/POCSAG

As far as power management goes, it looks like we can definitely reduce consumption from 16mA to slightly more than 1mA by keeping the radio in IDLE except when periodically sampling for the 480ms preamble. This will also fix the LCD fade out problem on CC430F6137-based watches, and depending on the settling time, we might be able to get even better lifetimes by shutting the radio off entirely between preamble-samplings.

[travisgoodspeed]

Average draw is down the 4mA by polling for the preamble, and that might be made a bit list. We're up to 24 hours of battery life.