programming arduino in pure c

Question

I'm trying to flash pure c-code to arduino Mega2560 board from linux using avr-gcc & avrdude. Compilation is done , now trying to flash using avr-dude, getting error as "avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00"

I used below command to produce hex file

avr-gcc -mmcu=atmega2560 -DF_CPU=16000000UL led.c -o led.elf

In file included from led.c:3:0: /usr/lib/avr/include/util/delay.h:95:3: warning: #warning "Compiler optimizations disabled; functions from won't work as designed" [-Wcpp] # warning "Compiler optimizations disabled; functions from won't work as designed"

And then

avr-objcopy -j .text -O ihex led.elf led.hex

finally for flashing

avrdude -F -V -c arduino -p ATMEGA2560 -P /dev/ttyACM3 -b 115200 -U flash:w:led.hex

FYI: port is correct & RX pin is blinking i.e connection is perfect between computer & board

Answer 1

In file included from led.c:3:0: /usr/lib/avr/include/util/delay.h:95:3: warning: #warning "Compiler optimizations disabled; functions from won't work as designed"

You should start by fixing this. Simply add -Os to the compiler command line. This means “optimize for size”, and is the standard optimization option used with Arduinos.

avr-objcopy -j .text -O ihex led.elf led.hex

If your copy of avrdude was compiled with libelf (like the one supplied with Ubuntu is), you don't need this: you can hand your elf file directly to avrdude.

avrdude -F -V -c arduino -p ATMEGA2560 -P /dev/ttyACM3 -b 115200 -U flash:w:led.hex

-F tells avrdude to not verify the device signature. -V tells it to not verify the upload. I wouldn't use any of these options unless I had a very good reason to do so. -c arduino is wrong: it selects the upload protocol used by optiboot (used, e.g., in the Uno). The Mega 2560 uses a different bootloader based on the “wiring” protocol. I would also add the -D option (disable auto erase) because I saw the Arduino IDE using it, and because without this option I get the error:

avrdude: erasing chip
avrdude: stk500v2_command(): command failed

In the end, the upload command ends up being something like:

avrdude -p atmega2560 -c wiring -P /dev/ttyACM3 -b 115200 -D -U led.elf