05 Oct 2013: 2nd revision, ADC (for Microphone) confirmed operational
Status update at the PCB page). The firmware for the Flying Squirrel is making good experimental progress. An interesting learning curve with the ADC has shown that it's necessary to carry out a hard reset of the STM32F ADC subsystem: it's insufficient to just power it off and on again, it's necessary to power off, reset, then configure and finally switch on. Once this was discovered (through random internet searches) reading the ADC was very straightforward, and also successful.
The next part was making it easy to read the ADC values, for debugging purposes. This was achieved by turning the STM32F USB gadget into a CDC ACM (USB Serial) interface. Copying one of the libopencm3 examples turned out to be very straightforward. Next up will be adding a Timer around the ADC as well as using DMA. Enough code exists: it just needs to be successfully plugged together.
The actual circuit around the LM13700 however is a different matter. The layout from March bears absolutely no relation to the example schematics in the datasheet! Fortunately, there are three LM13700 ICs now available to experiment with, as a means to create a working amplifier circuit.
Software-wise the microphone is turning out to be straightforward as expected, and the progress being made will help accelerate the development of the tougher task - the camera. The camera will require not just DMA but possibly some very tight post-processing and more. The fact that it's now possible to interact with the STM32F as a USB-Serial device will make debugging that much easier.
Update 17:00hrs - a video showing the progress made.