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Measuring AVR microcontroller interrupt latency

Nerd Ralph goes beyond the AVR data sheets to measure the interrupt latency of the ATtiny13 and ATtiny85 microcontrollers.

While section 4.7.1 is reasonably detailed, it has one significant error, and another important omission.  The error is the sentence, “The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles”.  All AVRs with less than 8KB of flash, like the ATtiny13, have no jump instruction.  They only have a relative jump “rjmp”, which takes two clock cycles.  This is obviously a copy/paste error from the datasheet of an AVR with  more than 8KB of flash.  Anyone familiar with the AVR instruction set would likely catch this simple error. The omission from section 4.7.1 is much harder to recognize until you carefully examine section 9.2 and figure 9-1 in the datasheet.

To test the interrupt latency, a program in assembler is written that can generate low pulses of different lengths using PWM.

See the details and results in the blog.


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