Version v0.03i

This is the final version in the 0.03 series.
Implements 10,000 seconds ring buffer (that's 2h 46m 40s), tested and working.
All known bugs have been fixed.
32-bit counter code was removed and entirely replaced with 64-bit code.
Yellow LED status now corresponds to GPS fix: blinking means no fix, off means fix.
Three separate GPSDOs have been built on separate breadboards and operated simultaneously,
with practically identical performance (better than +/- 1ppb stability over 100s),
validating the general hardware and software design.

GPSDO - v0.03g

Implements 16-bit PWM code to generate the Vctl to control the OCXO frequency, making the 12-bit I2C DAC redundant. Now purges the ring buffers in case of satellite signal / fix loss. Implements a command parser.
Work-in-progress: a 64-bit counter should allow for much longer measurement periods and simpler ring buffer management.

Version 0.02i

Improved code, better documentation. A BOM is available. Fully functional firmware, good for 1ppb (over 100s) accurate 10MHz square wave output. Operating status is reported through USB serial (115200 baud), Bluetooth serial (115200 baud) and OLED display. NMEA stream from GPS module is optionally available through USB serial or Bluetooth serial.

GPSDO v0.02c

Intermediate release before v0.02 final.

Initial release - GPSDO v0.01

This is the initial release of the GPSDO firmware. The code is very rough, but there are enough comments to make it understandable. And it works: the OCXO has its frequency stabilized at 10MHz +/- 0.01Hz and functions without locking up for > 24 hours.