a serial, full featured/generic bootloader
Features:
- usable at least for tiny2313
- requires/uses hardware USART
- uses the Watchdog
- fits into 128 bytes
- allows to read the flash and fuses
- allows to read and write the EEPROM and, of course:
- allows to flash new code (but not set fuses)
The usage of the watchdog is making this loader hopefully very useful:
If your application stops to work, the watchdog will reset and now you have the option to exchange your app via the serial interface. Standard, only bytes to send. No RTS/CTS/DTR things. If this does not happen, the app is started again.
As this loader is meant for environments where the serial interface is in use, you might add a command to your protocol that should activate the bootloader: then you get a cheap (just 128 Bytes) update path to your chip.
Of course you can still use a reset button or a reset line from your serial interface or use a power cycle: The important thing is: You don't need that.
I expect you can also use this nice on breadboards: Just two pins from a serial interface to (re-)program your chip...
Special thanks: ideas found everywhere, but especially to Ralph Doncaster for his picoboot:
https://github.com/nerdralph/picoboot/blob/master/picobootSerial.S
How to use it:
You need an application that speaks the protocol.
Currently there is only "mydude":
It implements most/all of the protocol, but lacks some timeout handling etc. so it is far from perfect: It might be useful to understand how the protocol works?
To compile mydude:
cc -Wall -o mydude mydude.c
At least it supports to upload a binary: You can generate a binary from a normal compile with
avr-objcopy -j .data -j .text -O binary blink blink.bin
with blink being the elf-File and blink.bin the result that can be uploaded:
mydude w /dev/ttyUSB0 blink.bin