Modification of the stock Arduino STK500v2 bootloader specifically for APM2 boards
There are several modifications
1. Correct sketch start if the board was rebooted due to watchdog timer
2. Fast sketch start if the USB cable is not sensed as being connected to the APM2 board
3. Flash the correct (ie, visible) LEDs in a more informative pattern in the bootloader
4. Removal of the !!! CLI feature of the stk500v2 bootloader
LED patterns to look for:
USB Connected, no traffic:
six slow blue flashes (while waiting for a serial character that does not come)
then.. sketch starts
USB Connected, some traffic:
any slow blue flashing is ceased and a short timer starts waiting for valid boot loader protocol
then.. sketch starts
USB Connected, valid boot loader traffic:
STK500 protocol packets (eg flashing a new sketch) cause rapid flashing of the blue LED for each packet
USB Not Connected
quick double blue flash
then.. quick single yellow flash
The sketch will have its own LED flashing pattern.
BUGS
If a USB cable is connected to power up the board, the boot loader starts the sketch instantly. This is because the USB cable detection takes a short time to stabilize, by then, the bootloader has moved on. This is not much of an issue as USB connection for the purposes of flashing the firmware causes another reset when the USB port is opened, thus the bootloader starts again anyway.
