Eureaka! I've got it! I have found the ideal frequency counter solution for my particular situation.
I have a TI DSP unit, the C5535 eZdsp development kit. It has a nice glow-in-the-dark LED display (able to show 2 lines of text, approximately 96x16 pixels I think) and is programmable in C. It has stereo in and stereo out.
Now, if only we could make a frequency counter that outputs some sort of audio signal, and if I could get the eZdsp to read that audio signal and convert it back to a digital display, I'd have a nice little stand-alone, glow-in-the-dark frequency counter that's programmable in C and can support all the features I need like IF offset or a memory function and drift indicator.
So, how to make a frequency counter that outputs decodable audio? My synapses were crackling as I considered crazy schemes like a binary frequency counter that fed its binary output into a parallel-to-serial chip, that then would be clocked by a signal from the eZdsp and would in turn generate a series of audio tones indicating the state of each bit, audio tones that would then need to be decoded in software... complicated, but not impossible.
Then I suddenly remembered seeing a recent PA2OHH page that described a soundcard-based frequency counter:
This uses a pre-scaler to divide the RF frequency to create an AF signal, which is then measured in software and multiplied by the previous division factor to reconstruct the original RF frequency. Brilliant!
The PA2OHH idea provides the last piece of the puzzle. If the idea works on a PC, it must work on the DSP unit as well. And, since the DSP has stereo microphone inputs, I can use one audio channel for the frequency counter, and one audio channel for signal processing of the receiver audio! Woo-hoo! A frequency counter and DSP in one small box.
Can't wait to start.