I spent the whole day today getting a gcc / makefile based environment to work on Mac OS X wth the latest Nordic tools for the Bluetooth processors I'll be using in the GPS dongle and the main device.
I made a page here on Hackaday documenting my results. I hope I'll save someone else some time.
I also quickly tested my solar cell and DC/DC converter. It turns out that the LM2596 buck converter (with adjustable voltage and current limiting) has a minimum input voltage of 7V, and my solar cell has a nominal voltage of 6V. When I turned down the voltage on the DC/DC input, the current limiting stopped working, but the voltage limit still worked.
I tested different loads on the solar cell, and best power in the spring sun was around 123 ohm load, 6.5 V, 53 mA (345 mW).
I realized that since the solar cell won't be able to give more current than the LiPo battery can swallow, I don't need current limiting from my DC/DC converter.
I read an interesting design note about AdaFruit's solar LiPo charger. It pointed out the importance of keeping the solar cell at a good operating point (drawing too much current decreases the power output significantly), and also that the optimal voltage doesn't change much under different illumination, so trying to keep the solar cell at a constant voltage of around 6-6.5 volts is sufficient to get good efficiency. I now have a vague idea of modifying the LM2596 buck converter current limited to get input from the input voltage instead of the current, and decreasing the output voltage if the input voltage goes below 6V. But that's for another day, now my focus is on the Bluetoooth software.
I also discovered that there is a BLE profile called "Navigation and Location". It would be nice if I can make my GPS/Compass dongle compatible with that profile.