Can I Program my Photon over UART with a Bus Pirate attached to a Raspberry Pi?
You can flash firmware using the YMODEM protocol by entering setup mode and pressing ‘f’. Alternatively, if you have 0.4.2 or later, this mode can be triggered automatically by setting the USB line rate to 28800 baud. This is still an experimental feature and consequently hasn’t been documented.
Another alternative is to use DFU mode. Again,with 0.4.2 it’s possible to trigger DFU mode automatically as part of the make program-dfu goal.