Hello,
After the C11 spec was finalized, GCC added a bunch of new built-in “__atomic_X” functions to replace the older “__sync_” functions. These atomic functions are generally used by <stdatomic.h> headers, as they were designed to adhere to the C11 memory model, but there’s nothing preventing their use in "regular" code. These built-ins are rather convenient, as they allow for atomic manipulations of regular data types, which is useful when dealing with data which is shared between threads (or the main program and an ISR in the case of an MCU). With these functions, it would no longer be necessary to declare shared global variables as “volatile”, and it would no longer be necessary to explicitly disable and re-enable interrupts when dealing with types larger than the native word size. Currently, these “__atomic_X” functions (as well as the older “__sync_” counterparts) are not supported on the AVR. When the atomic operations aren’t natively implemented by GCC on a specific platform (either due to hardware limitations or because GCC just hasn’t implemented them yet), GCC automatically converts calls to the built-in “__atomic_X” functions into regular function calls which are to be resolved by an external library. This library is called “libatomic” and is supposed to implement the required routines in a way which is specific to the target platform (perhaps using locks or disabling interrupts). The issue is that no such library exists for the AVR, so any use of the “__atomic_X” functions ultimately results in undefined references at link time. The reason I’m posting here is because I’ve created a libatomic library for the AVR. In reality, it’s just a single C file which implements the required “__atomic_X” functions by means of saving/disabling interrupts, performing the operation, then restoring interrupts. With this library, I was also able to include a portable version of the <stdatomic.h> header which allows for the successful use of C11 atomic types! I would like to get this merged into avr-libc, as it seems to be the most sensible place for it (I think). However, I’m not familiar with the process, coding requirements, etc… I am willing to release it under whatever license is required, which I assume would be BSD. This would be good also because the portable <stdatomic.h> header file that I used is already BSD licensed. By implementing the libatomic library and (optionally) including a <stdatomic.h> header, we would support a fully portable way of dealing with atomic types, which I think would be a good thing. Do you think this is the right place for such an implementation? If not, could you direct me? I'm not familiar with the general development process here, so forgive me if I'm out of line. Jake _______________________________________________ AVR-libc-dev mailing list AVR-libc-dev@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-libc-dev
