avr_boot
========

SD card bootloader for atmega processors

As easy as it can get! I spent days with this. Hopefully you wont!

- for any ATMega with 4096kb Bootloader
- uses Petit FatFs R0.03 for FAT12, FAT16, FAT32
- looks for FIRMWARE.BIN and flashes it nearly instantly
- without any interference to your application
- no CRC Check and no version bytes in EEPROM (see KISS)

### Boards Manager installation

avr_boot is integrated in Arduino IDE version 1.6.4 or greater!!! [See here for instructions.](https://github.com/zevero/avr_boot/tree/gh-pages)

### Manual installation

This is with avr-gcc and avrdude under linux with an Atmega1284p and AVRISP mkII! Adaption to your case (WinAvr, another Atmega, another flash-tool) will not be complicated...

- adapt Makefile
  - MCU_TARGET: Your atmegaXXX
  - BOOT_ADR: in bytes not words!
  - F_CPU: CPU Frequency (not critical. A higher value will work as well)
  - SD_CS_PORT: Data Register of the SD CS pin(see the datasheet for your microcontroller)
  - SD_CS_DDR: Data Direction Register of the SD CS pin
  - SD_CS_BIT: Bit of the SD CS pin
  - USE_LED: For debugging 0...deactivate or 1...active
  - USE_UART: For debugging 0...deactivate or divider (UBRR) for baudate see http://wormfood.net/avrbaudcalc.php
- update spi_pins.h with the SPI pins of your microcontroller if not already defined
- if using USE_LED adapt LED-pins in asmfunc.S
- if you want to add FAT12 adapt pff/src/pffconfh.h (default ist FAT16 + FAT32)
- if you want to support lower case filenames adapt pff/src/pffconfh.h (default is uppercase)
- if you prefer another filename instead of FIRMWARE.BIN adapt main.c 
- make (you may need to do "sudo apt-get install avr-libc gcc-avr")
- set fuses: avrdude -c avrispmkII -p m1284p -U hfuse:w:0xda:m
  - find high fuse in http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega1284p
- flash: avrdude -c avrispmkII -p m1284p -Uflash:w:./avr_boot.hex:i -Ulock:w:0x3F:m 

### Put your sketch on SD card 

- in Arduino IDE go to File > Preferences and check "Show verbose output during compiliation"
- compile sketch and find the location of your /tmp/buildxxx/sketch.cpp.hex
- make bin file: avr-objcopy -I ihex -O binary sketch.cpp.hex FIRMWARE.BIN
- copy the file into the root of an SD (FAT16/FAT32)
- put it into the SD slot of your ATmega
- reset it
- it might already have happend!

### Bootloader sizes
Compiled under linux for atmega328p / atmega1284p
 - 3674 / 3724 bytes
 - 3984 / 4034 bytes debugging with USE_LED
 - 3992 / 4052 bytes debugging with USE_UART

### Tested successfully on
 - ATmega168
 - ATmega328P
 - ATmega32u4
 - ATmega1284P
 - ATmega2560 (see issue #2)

### Serial support - Help wanted
it should not be impossible to fit a normal serial bootloader (with automatic baudrate detection?) into the remaining bytes ... help is appreciated!

### KISS
If you wish you *can* add CRC Check or versioning with EEPROM *but* I prefere to keep things simple. avr_boot will reflash your FIRMWARE.BIN as long as it is present.
Is this a problem? No! It happens nearly instantly and only differing bytes are flashed really.
You may consider putting your logic into your application and perform a CRC Check after the fact to inform the user and delete or rename FIRMWARE.BIN

### Thanks to
- https://github.com/per1234 - Boards Manager Installation and help with differenct MCUs
- http://elm-chan.org/fsw/ff/00index_p.html
- Wilfried Klaas for the MCSDepthLogger https://github.com/willie68/OpenSeaMapLogger
- https://github.com/mharizanov/avr_boot
- https://github.com/osbock/avr_boot
- and others???

### Alternatives

- https://spaces.atmel.com/gf/project/sdbootloader/
- https://github.com/thseiler/embedded/tree/master/avr/2boots
- http://www.mikrocontroller.net/articles/MMC/SD_Bootloader_f%C3%BCr_AT_Mega

... call me stupid, but I passed several days debugging those - without success ...