Arduino millis timer interrupt code#

Timer2 Interrupt Service is invoked by hardware Timer 2 every 1 ms = 1000 Hz ++overflowCount // count number of Counter1 overflows TCCR2B = bit (CS20) | bit (CS22) // prescaler of 128 GTCCR = bit (PSRASY) // reset prescaler now TIMSK2 = bit (OCIE2A) // enable Timer2 Interrupt OCR2A = 124 // count up to 125 (zero relative!!!!) So we count 125 of them, giving exactly 1000 µs (1 ms) 16 MHz clock (62.5 ns per tick) - prescaled by 128 Timer 2 - gives us our 1 ms counting interval TIMSK1 = bit (TOIE1) // interrupt on Timer 1 overflow TimerTicks = 0 // reset interrupt counter TimerPeriod = ms // how many 1 ms counts to do

these are checked for in the main program If time is up, we turn off both Timers 1 and 2, calculate the total count (by multiplying the number of overflows by 65536 and adding in the remaining counts) and exit. In the Timer 2 interrupt we see if time is up (basically whether the required number of milliseconds is up). Note that Timer 2 has a higher priority than Timers 0 and 1, so neither the millis() timer, nor the Timer 1 counter will take precedence over this interrupt. Since 8 µs times 125 gives 1000 µs, that means we get interrupted exactly every 1 ms. This interrupt gives us a chance to see if our counting period is up. So we configure Timer 2 to count up to 125 and then generate an interrupt. The pre-scaled clock will then 'tick' every 8 microseconds (since the clock itself runs with a period of 1/16000000 or 62.5 ns).

It is set up to take the internal clock (normally 16 MHz on a Uno), and 'pre-scale' it by dividing it by 128. The counts are meaningless unless we know over what interval they occurred, which is what we use Timer 2 for. Timer 2 - used to work out a timing interval However, of course, a longer timing period takes longer to execute. You could also time it for 1/10 of a second (giving you a count of 500) and then multiply the result by 10, again giving you a figure of 5 kHz.Ī longer timing period will give higher accuracy, and also average out any small variations during the sample time.

Arduino millis timer interrupt code#

The example code below provides a 'frequency counter' which counts the number of events which cause a rising edge on digital pin D5 during a specified interval.įor example, if you put a 5 kHz signal on pin D5, and time it for one second, the count will be 5000. You can use these timers easily enough by using the analogWrite function - that just generates a PWM (pulse width modulated) output on the various pins that the timer hardware supports.īut for a more in-depth analysis, let's look at using the timers/counters in our own way. This provides you with the figure that the millis() function returns. This is used to count approximately every millisecond. Timer 0 is set up by the init() function (which is automatically called by the code generated by the IDE, before setup() is called). The Atmega328 (as on the Arduino Uno) has three timers/counters on-board the chip. This page can be quickly reached from the link: