I'm looking at interrupt setup code written by someone else. I understand the logic operators to get the flag bits set or cleared, but I'm having problems locating documentation that explains the meaning of the bit flags. Is there a recommended "go to" document/url to get a good understanding about interrupt flags and how they are used?
For example ...
TCCR2A = ((1 << WGM21) | (0 << WGM20));
TCCR2B = (( 1 << CS22 ) | ( 1 << CS21 ) | ( 1 << CS20 )); // 1/2^10
ASSR &= ~(1<<AS2);
TIMSK2 = (1 << OCIE2A); // Enable TIMER2 compare Interrupt
TCNT2 = 0;
OCR2A = TICK_DIVIDER; // must be loaded last for Atmega168 and friends
... where do I go to understand what WGM21 or ASSR mean and how they are used?