Question: Is the PIC firmware flashing possible at runtime? I.e. using the USB connector? Or would it require un-soddering the PIC and hooking it to a programmer? The reason to ask is i would ideally like to be able to change the serial# to include information about the boards position in the cluster.
Currently the PIC is programmed by pressing the PICKit3 pins against the ICSP pads on the board - no need to unplug as it needs power on. After I add bootloader code that supports both I2C and USB it will also be re-programmable for most code sections via the USB, using either a special utility or perhaps the cgminer driver (probably by placing a firmware file in the right directory).
If programming via the PICKit3 you would need to disconnect the fan briefly as well since the fan tachometer output shares an ICSP line. If using a 2 pin fan with no tach feedback then this doesn't apply.
Another way to ID position would be to connect I2C one- by-one noting each serial# as they register. Since I2C is a bus and not daisy chain there is no built in way to determine position and address.