A while ago, I built a reverse geocache box from a broken GPS wristwatch (Keymaze 700 trail) found in an electronics recycle bin. For that, I had to upload a custom firmware in the STM32F103 microcontroller through JTAG (with a buspirate and OpenOCD).
The GPS wristwatch "CW Kalenji 700 gps", is very similar to the "Keymaze 700 trail", it has the same microcontroller and thus can be easily reprogrammed. Rather than having to open it in order to program it by JTAG, it would be much more convenient to use the built-in firmware upgrade mechanism of the watch.
The information needed for this project were gathered by reverse engineering the watch in two different ways :
Hardware : by studying the pcb of the watch to find out the connections between the microcontroller and the various peripheral. Mainly on another watch ("W Kalenji 300 gps") which has the same pcb.
Software : By disassembling the original firmware and bootloader.
more here.............http://renaud.schleck.free.fr/montre_gps.php
The GPS wristwatch "CW Kalenji 700 gps", is very similar to the "Keymaze 700 trail", it has the same microcontroller and thus can be easily reprogrammed. Rather than having to open it in order to program it by JTAG, it would be much more convenient to use the built-in firmware upgrade mechanism of the watch.
The information needed for this project were gathered by reverse engineering the watch in two different ways :
Hardware : by studying the pcb of the watch to find out the connections between the microcontroller and the various peripheral. Mainly on another watch ("W Kalenji 300 gps") which has the same pcb.
Software : By disassembling the original firmware and bootloader.
more here.............http://renaud.schleck.free.fr/montre_gps.php