Because I like to use table-driven dispatch routines in ASM, for speed and brevity, I'd probably write the MAIN component in ASM, and use compiled modules from the 'C' compiler as macros or subroutines. I'm not sure how easy that would be, however.
C subroutines to an asm program is dead easy once you have figured out how to do it; however no (keil?) C will work if the main is in asm. This can easily be handled by the following:

void main void
{
assemblermain();
} 

anyhow
void main void
{
while (1)
  {
  task1();
  task2();
  task3();
  task4();
  }
}

comes out identical whether in asm or C

Just a note: once you realize the advantages of C you will end up writing 75-100% of your code in C. the tough part (at least it was for me) is to realize that 75-100% of any code does not need to be super effcient.

Erik