spectrum analyser frequency control

The picture shows the control part of the spectrum analyser.
I try to make it a bit more sophisticated than the control I found in several designs.
Most designs use a potentiometer to set the center frequency, the sweep speed and the amplitude of the sweep signal. The better onces include a frequency counter.

The concept:
The Sawtooth generator is started by the PIC micorcontroller. If one cycle has finished it notifies the PIC. This way the PIC can calculate the sweep frequency accurately.
During the sweep the PIC counts the LO/256 frequency it receives from the tuner. Now the PIC is able to calculate the center frequency. This frequency is compared with the intended center frequency. Depending on this comparison an up or a down signal is send to the integrator. The integrator provides a DC offset voltage that sets the center frequency. The signal from the sawtooth generator is added to the offset voltage. Usually the VCO in the tuner is not linear. To compensate this non linearity a linearizer is added.

I am not sure the concept will work. It may be too slow. The regulation may be too crude.Experimentation is needed to find out.