[GPS_Standard] Proportional and/or integral adjustment

[Dave Platt]

Bob Bownes wrote:
> Dave,
> 
> That would certainly help avoid the dithering problem.
> 
> I _think_, if I read you right, it would also help my drift after
> unlock problem, in which, unless I crank the Sample Size (S) down, it
> won't lock again because the DAC delta is less than the drift delta.

Yes, I think it would.  It could help reduce the risk of unlocking in
the first place (by tracking more accurately) as well as speeding up
the re-lock if an oscillator drifts rapidly or jumps frequencies.

> An alternate might be an 'Initial Lock mode' in which the value of
> correction is proportional to the freq difference, much as you say.

Yes, a two-mode-of-operation feature (with some logic for automatically
switching between modes) could be useful, as well.  It would speed the
process of establishing an initial lock at turn-on time, while
allowing long-term stable operation with different parameters.

Implementing dual-mode, without requiring lots of nasty code
changes (e.g. duplicating lots of logic, or adding if/then/else
on every parameter lookup) might be a bit tricky to do.
Perhaps this could be done by "shadowing" the various sets of
EEPROM parameters into two different banks of the microcontroller
RAM, accessing the variables from RAM rather than EEPROM, and
doing the mode-switch by just switching RAM banks?