I have started to play with and arduino UNO quite recently (without any prior experience with micro-controllers). I would like to use emacs instead of the IDE, and I'd also like to know what the IDE does under the hood, in order to be able to write my own makefile. The tutorials I've found are either outdated, or are presented as a series of steps without any explanation. I'd appreciate it if someone could explain to me how the whole compliation/linking/upload process works using gcc-avr and avr-dude, and how it is used by the IDE.
If you want an exact duplication of what the IDE does but want it driven from the command line, that's what Ino is for. The full Arduino build process involves copying a lot of files from a lot of places, and is generally not trivial to duplicate.
If you're ready to let go of .ino files and the Arduino libraries, you get a much simpler toolset. avr-gcc compiles, avrdude uploads, and you're done. Here's one of my makefiles from a simple project:
CXXFLAGS=-Wall -Wextra -mmcu=atmega1284p -Os
↹@rm -f $(BINARY) $(BINARY).hex $(OBJECTS)
↹@avrdude -c usbasp -p m1284p -U flash:w:$<:i
↹@avr-objcopy -j .text -j .data -O ihex $< $@
.PHONY: all clean upload
If copying-and-pasting, be sure to replace all "↹" with tab characters.
I have created a repository with my buildsystem on Github.
Here is a high-level overview of Arduino's compilation process, for folks like me who found this post while hunting for one:
The compilation process
The arduino code is actually just plain old c without all the header part (the includes and all). when you press the 'compile' button, the IDE saves the current file as arduino.c in the 'lib/build' directory then it calls a makefile contained in the 'lib' directory.
This makefile copies arduino.c as prog.c into 'lib/tmp' adding 'wiringlite.inc' as the beginning of it. this operation makes the arduino/wiring code into a proper c file (called prog.c).
After this, it copies all the files in the 'core' directory into 'lib/tmp'. these files are the implementation of the various arduino/wiring commands adding to these files adds commands to the language
The core files are supported by pascal stang's procyon avr-lib that is contained in the 'lib/avrlib' directory
At this point the code contained in lib/tmp is ready to be compiled with the c compiler contained in 'tools'. If the make operation is succesfull then you'll have prog.hex ready to be downloaded into the processor.