[sdiy] oscillator auto calibration

[Daniel Kruszyna]

I'm trying to auto calibrate an efm vco4e using an avr microcontroller.
The avr controls 2 pitch control voltages: 1 with 0V..10V range and
another with -1V..1V range. The dac is 12bit. The squarewave output
clocks a timer in the avr so I can measure the number of cycles per
time period.

I want to set the desired frequency with the 0V..10V control voltage
and use the -1V..1V voltage to correct any error.

The frequency error is (f_measured - f_setpoint). However, to use a
standard control loop, I need to calculate
(log2(f_measured) - log2(f_setpoint)). Does this sound correct?
Is there another method that avoids calculating log2? (I'm using
fixed point.) Are there any other auto calibration projects out
there to reference?

-- Daniel