First off I suggest that you stop trying. You are supposed to write in C when you choose to use a C compiler. In such environment the compiler is left to decide as the best usage of the machine CPU resources.

If you need to access the CPU hardware in a way that is suitable for assembly language usage then write in assembly language!!!

With any C compiler it is possible to call an assembly language routine. So if you have some time critical code that must be written in assembler go ahead and make it this way and then call it from the C code.

Read the manual for your C compiler. Any decent commercial compiler will describe assembly language interfacing in the manual.

Michael Karas