@ sign in C variable declaration

Question

I found this header file for PIC microcontrollers by the name of pic1250.h and I\'m unable to get the hang of some syntax used in it.

The source for the file is:

Answer 1

In addition to what has already been said, please note that the non-standard @ operator is a superfluous feature. You can achieve exactly the same behavior with standard C:

#define RTCC (*(volatile uint8_t*)0x0001u)

Since the variables in this case are hardware registers, you don't need to worry about allocation, they are already present in the hardware. If you want to allocate a variable at a custom address, there should be a linker file of some kind to fix that (since the @ operator only solves specific allocation for variables, not for code).

The main reason why many embedded compilers come up with some non-standard operator like @ is because they can't think outside the box when designing the debugger. They expect some sort of variable to be present in the object file which is fed to the debugger, but if you use #define, no such "debug information object" is allocated.

If the debugger looked at the source code instead, or better yet, had MCU awareness built-in, then non-standard code like this wouldn't be necessary. High quality tools from companies that focus solely on debuggers always come with built-in support for viewing register maps.