I was trying to determine if it is possible to remotely flash firmware on an ATmega2560 microcontroller using a micro SD card. I came across this repository of an ATmega2560 bootloader that flashes the microcontroller’s flash memory when a particular address on the EEPROM (Address: 0x1FF) is set to the value ‘0xF0’.
When the microcontroller is reset, if the EEPROM value(at address ‘0x1FF’) is set to ‘0xF0’, the bootloader looks for a file ‘firmware.bin’ on the SD card and flashes the microcontroller with the new firmware.
I had to make minor modifications to make use of this bootloader. I changed the Chip Select pin number of the micro SD Card (there are tutorials that explain how SD cards are interfaced to microcontrollers) in the macro definition to match that of the Adafruit Music Maker shield (the micro SD holder’s chip select pin is connected to Digital Pin 4 of the Arduino. This corresponds to pin 5, PORTG on the ATmega2560. Source: Arduino Mega 2560 schematic).
In the file asmfunc.S, I changed the CS pin to pin 5 on PORTG:
I also had to change the pin number of the LED used to indicate the progress of flashing the microcontroller by the bootloader.
After recompiling the bootloader’s source files, I flashed the new bootloader using AVR ISP MK II. I also had to make sure that the BOOTRST fuse was set in the ATmega2560’s fuse settings.
I compiled an LED blinking sketch and converted it into a binary file by executing the following command:
Note: The Arduino IDE compiles and stores its hex files in a temporary directory. In order to save the hex file upon compilation, edit the IDE preferences after closing the IDE. The preferences text file can be located at File–>Preferences
A line build.path has to be added to the preferences file. I included the path where the output of the compiled Arduino sketch would be located. I used Atmel Studio to convert the Arduino sketch’s hex file to a binary file (the avr-objcopy command shown in the above code snippet). I copied the binary file onto a micro SD card and inserted into the music maker shield’s micro SD card holder.
I made use of this sketch to set the value ‘0xF0’ at the address ‘0x1FF’. Upon reset, the bootloader flashed the microcontroller with the binary file located on the SD card.
Things to investigate:
1) When I was looking for a bootloader that would flash a microcontroller from an SD card, I read about problems encountered by others. I found out that people had problems using certain types of micro SD cards. I did have a hard time getting the bootloader working but it was due to the fact that I did not set the BOOTRST fuse.
Do let me know if you have used this bootloader or something similar in the past.