Question

I know that OCIE0A=0001 in binary, so would (1<<OCIE0A) just be 0010? I see this being used quite frequently, what is the reason for setting a register to (1<<OCIE0A) and not just setting it to 0010 directly?

Answer 1

Judging from the results of a Google search, it appears* to be the name for the bit that controls “Timer/Counter Output Compare Match A Interrupt”* in the “Timer/Counter Interrupt Mask Register”* of a “8 bit AVR Microcontroller”* Its usage is as follows*:

TIMSK0 |= _BV(OCIE0A);  // enable compare A interrupts 
TIMSK0 &= ~_BV(OCIE0A); // disable compare A interrupts 

Where TIMSK0 is* the Timer Interrupt Mask Register*. OCIE0A is an identifier that (to someone familiar with AVR code*) is more immediately understandable* than TIMSK0 |= 2*.

They using bit identifiers instead of masks since any halfwit compiler can optimize them to the same thing for bit->mask, but going from mask->bit is harder*. So by leaving it as the bitid, it’s easy and fast for all usages*.

On an unrelated note, numbers are values stored as binary in the computer. “Decimal” and “Hex” are representations of those values. So no, OCIE0A is not “hex”. It is a symbol that represents the bit offset of a flag, with the value of 1.

_{*assumptions everywhere, I know nothing}