2boots
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This is a proof-of-concept dual bootloader for Atmel AVR atmega chips.
It combines a serial bootloader and a mmc/sd card based one in the
same 2kb of flash memory that is normally used by the arduino serial
loader alone.

You might ask Why? Well, I have quite a few arduino "in the field".
I can simply drag a .hex file to an SD card, insert it in an SD shield,
and field-upgrade my boards without additional hardware. At the same time,
I can connect the serial port and start developping with the normal Arduino
IDE.

Features:
* Uses just 2kb of flash, so it fits into the normal boot block of most atmegas
* Serial bootloader is arduino compatible (avrdude / stk500v1)
* MMC bootloader can read directly a *.hex file from an SD/MMC card
* Supported are FAT16 formatted cards up to 2GB in size (no SDHC yet)
* All of ladyada's fixes to the original bootloader are included