I'm writing a simple library for my AVR, and I wanted to try to use a macro function to define my baud-rate. A lot of the functions in the AVR's library use the macro F_CPU as well as the one I want to write.
Here's what I have for the macro definition and my supposed implementation:
#define BAUD_SELECT(baud) ((F_CPU)/(2*baud)-1)
myubrr = BAUD_SELECT(38400);
I have tried using #define F_CPU 8000000UL, and also in the make file as -D"F_CPU 8000000UL" but I always get the same error at the implementation line.
expected ')' before numeric constant
I'm sure it has something to do with my abuse of #define, and that the macro definition is in a header file, the implementation in the appropriate .c file, and the F_CPU definition either in the makefile or another main.c file.
EDIT I made the parenthesis change as suggested and ran the preprocessor and found the output file (atleast I think)
unsigned int myubrr = ((8000000UL 1)/(2*(baud))-1);
It places an extra 1 where F_CPU should be, I'm not experienced with the preprocessor so I'm not sure how to make it not do that, but perhaps that is the problem?
This works fine for me:
#define BAUD_SELECT(baud) ((F_CPU)/(2*(baud))-1)
unsigned int myubrr = BAUD_SELECT(38400);
when I compile with
$ cc -c -DF_CPU=8000000UL t.c
The extra parens don't really matter in this specific case, thought they're a good idea in general. So there's something else going on. Perhaps there's another definition of F_CPU in some other header file that is overriding your definition of F_CPU