Question

Sory for bad English, please.

I need write a time-critical piece of code (a strict part of software protocol implementation via bit-bang) that uses delays. C preprocessor at the compile time can compute the number of clock cycles (with F_CPU macro) for a delay, so I need to implement a assembler delay code for unknown number of cycles.

But GCC provide very useful function __builtin_avr_delay_cycles(unsigned long cycles) that make delay exactly cycles clock cycles for defined F_CPU frequency.

Question. Is there way to use __builtin_avr_delay_cycles within inline-assembler code?

Note. Bypass way is like this:

__asm__ (...);
__builtin_avr_delay_cycles(...);
__asm__ (...);

but the compiler can make some code around __asm__ pieces. It is bad for me, I need to control each clock cycle.

Answer 1

No, compiler built-ins are not real functions and cannot be called from assembler, nor will the compiler recognise them within assembler.