Go Down

Topic: Timer Interrupts on Due (Read 102952 times) previous topic - next topic

I have done a few modifications to the Due_Timers library, but I can't contact Ivan.  I want to help with this library.


Sorry for the delay (if you sent me an email, I haven't got time to answer it yet...)

About the changes, I will be happy to review it and commit to the master branch of the repository. Could you kindly submit a new commit and a merge request?

Arduino DueTimer | https://github.com/ivanseidel/DueTimer
Arduino Thread | https://github.com/ivanseidel/ArduinoThread


Because there are some people with this problem, I made a modification on DueTimer that will allow you to put to work both Servo and DueTimer together.

I didn't have time to test, but I'm pretty sure everything will work just fine.

Here is the documentation on how to make it work: https://github.com/ivanseidel/DueTimer#compatibility-with-servoh
Arduino DueTimer | https://github.com/ivanseidel/DueTimer
Arduino Thread | https://github.com/ivanseidel/ArduinoThread


Hey just wanted to say thanks to all on this thread. I just finished building a theremin like instrument with an Arduino Due
http://2manyprojects.net/theremin-1 .

I would never have completed this project without all the info I got here. It uses two different timer interrupts, one at 44.1 kHz, and one every 20 mS. The 44.1 kHz is for actually playing the tone using granular synthesis ( only one grain ), I got started with the "RCArduino Quick And Dirty Synth for Arduino Due"

The 20 mS interrupt is used to control a servo, this is done to demonstrate how to play a song. ( it will make sense if watch the video here http://2manyprojects.net/rtttl ). 

I also wrote up a tutorial on making a LED flash SOS using timer interrupts.
http://2manyprojects.net/timer-interrupts .

Thanks Again


Using this code, you can set a timer for any of the ISRs TC0_Handler through TC8_Handler, see table of parameters below. It is possible to use the timers without a physically mapped pin, such as TC1 channel 0 (TC3_Handler) shown here:

Code: [Select]

volatile boolean l;

//TC1 ch 0
void TC3_Handler()
        TC_GetStatus(TC1, 0);
        digitalWrite(13, l = !l);

void startTimer(Tc *tc, uint32_t channel, IRQn_Type irq, uint32_t frequency) {
        TC_Configure(tc, channel, TC_CMR_WAVE | TC_CMR_WAVSEL_UP_RC | TC_CMR_TCCLKS_TIMER_CLOCK4);
        uint32_t rc = VARIANT_MCK/128/frequency; //128 because we selected TIMER_CLOCK4 above
        TC_SetRA(tc, channel, rc/2); //50% high, 50% low
        TC_SetRC(tc, channel, rc);
        TC_Start(tc, channel);

void setup(){
        startTimer(TC1, 0, TC3_IRQn, 4); //TC1 channel 0, the IRQ for that channel and the desired frequency

void loop(){

Here is the table of parameters:

ISR/IRQTC        ChannelDue pins
TC0TC002, 13
TC1TC0160, 61
TC3TC10none  <- this line in the example above
TC6TC204, 5
TC7TC213, 10
TC8TC2211, 12

Is there any interference between Timer interrupts and arduino's Serial library? Using this function (see above) to set any timer except TC1 CH0 will cause Serial.available() to stop functioning. Is this a known problem?

Best regards,


Aug 05, 2014, 11:53 am Last Edit: Aug 06, 2014, 05:22 pm by WesBrooks Reason: 1
Very useful thread, thanks all.

What timers are used by the arduino in it's default state?

Were the problems caused to the servo library by the timer library shared due to both libraries changing the point at which a timer was reset?

Can the code that runs the triggering of the interupt can be considered to be  running in parallel to the other code in the script?

So the interupt function itself doesn't run in parallel. If this is the case this gives you a specific time slot in which the interupt function would have to complete before the next interupt triggers. If an interupt function call extents beyond the end of the next interupt what happens?

As the called interupt function is running in series with the existing script then the size of the interupt function itself needs to be carefully consedered in order to avoid degrading the performance of the remaining script on the arduino. Is there a resource for estimating the number of clock cycles descrete segments of code take? I've read that multiplication can take place in one clock cycle the number required for a case statement,  function call, and changing a global variables value would be a good starting point.

If someone could check if I've got the right end of the stick with the following right it would be helpful!

So the 'click' for each timer is coming in at the following frequencies:

(master clock freq) / (clock divider)

1 ~ Divider=2 ~ 42MHz
2 ~ Divider=8 ~ Master clock / 8     ~ 10MHz
3 ~ Divider=32 ~ Master clock / 32   ~ 2.6MHz
4 ~ Divider=128 ~ Master clock / 128 ~ 0.66MHz

As the timer is a 32 bit timer the maximum time between interupts is:

((clock divider) * 4294967295) / (master clock freq)

1  ~ 102 sec
2 ~ 409 sec
3 ~ 1640 sec
4 ~ 6540 sec

As RA is the number of 'clicks' until an interrupt is triggered, and RC is the number of steps until the timer is reset the frequency of interupts can be much higher. RA could be 1, and RC 2, meaning the click sequence would be:

Timer sequence: 0 - 1 - (reset to 0) - 1 - (reset to 0)
Interupt sequence: 0 - Interupt - 0 - Interupt

So the minimum time between of interupts is:

((clock divider) * 2) / (master clock freq)

1  ~ 47 ns ~ (21 MHz) ~ 4 Clock cycles
2 ~ 190 ns ~ (5.25 MHz) ~ 16 Clock cycles
3 ~ 762 ns ~ (1.31 MHz) ~ 64 Clock cycles
4 ~ 3050 ns ~ (0.328 MHz) ~ 256 Clock cycles

(I'm having another read through this thread to see what questions I can answer for myself - 9 pages is a fair bit to digest in one pass!)

EDIT: 32 bits is 4294967295, not 65535!

Hi - have just about run out of ideas.

Problem: Trying to output a 8mhz signal on a pin - any pin does not matter.

Used some of the original code in this thread and go up to 667 via the irq - but believe I can get the actual timer/clock logic to do it for me.

Currently I have a probe on digital pin 5 which corresponds to TIOA6 which is TC2 channel 1.

Was not getting anywhere so decided to use a simple example to see if it worked - I downloaded Ivans Library and modified the simpleTimer example as follows (to use Timer6)

Zip on pin5 - the line goes high and that is it.

Q1. Ivan - will your library enable TIOA6 (pin 5) with a clock?

Q2. Does anyone have a simple example for the Due that outputs a signal without using an interrupt (getting the hardware to do it) - any example just to get me over the hump.

Q3. Using Ivans example, it uses an IRQ - does the use of an IRQ by any chance disable the internal CPU's toggling of the pin?

BTW - I have read the atmel specs, been googling but am not getting anywhere.

Also BTW - I have done a simple check on pin 5 with a variation of blink - the line goes high/low without a problem.

Modified example:

#include <DueTimer.h>

int myLed = 13;

bool ledOn = false;
void myHandler(){
   ledOn = !ledOn;

   digitalWrite(myLed, ledOn); // Led on, off, on, off...

void setup(){
   pinMode(myLed, OUTPUT);

   Timer6.start(50000); // Calls every 50ms

void loop(){

      // I'm stuck in here! help me...

Aug 24, 2014, 01:45 am Last Edit: Aug 24, 2014, 12:04 pm by stan_w_gifford Reason: 1
Getting closer.

Found the following sample which I have modified - now get 4mhz.

Note that the wave is pretty good - but now and again there is a little 'pause' - suspect CPU best busy updating another timer or something.

#ifndef DUE_SERVO_H
#define DUE_SERVO_H

#include <Arduino.h>

#define PWM_DUTY_MIN    1
#define PWM_DUTY_MAX    2400

void writeMicros(int pin, uint16_t dutyCycle);
void initServo(int pin, uint16_t dutyCycle);


#define PWM_CLOCK       48000000
#define PWM_PERIOD      20

static bool PWMEnabled = false;

void initServo(int pin, uint16_t dutyCycle) {
        if(!PWMEnabled) {
                PWMC_ConfigureClocks(PWM_CLOCK, 0, VARIANT_MCK);
                PWMEnabled = true;
        const PinDescription *config = &g_APinDescription[pin];
        int channel = config->ulPWMChannel;
        if(channel == NOT_ON_PWM)

        PWMC_ConfigureChannel(PWM_INTERFACE, channel, PWM_CMR_CPRE_CLKA, 0, 0);
        PWMC_SetPeriod(PWM_INTERFACE, channel, PWM_PERIOD);
        writeMicros(pin, dutyCycle);
        PWMC_EnableChannel(PWM_INTERFACE, channel);

void writeMicros(int pin, uint16_t dutyCycle) {
        int channel = g_APinDescription[pin].ulPWMChannel;

        if(channel == NOT_ON_PWM)

        if(dutyCycle < PWM_DUTY_MIN)
                dutyCycle = PWM_DUTY_MIN;
        if(dutyCycle > PWM_DUTY_MAX)
                dutyCycle = PWM_DUTY_MAX;

        PWMC_SetDutyCycle(PWM_INTERFACE, channel, dutyCycle);

#define SERVO_PIN 6
bool high = false;

void setup() {
        initServo(SERVO_PIN, 10);

void loop() {


OK getting somewhere - found out that the PIO_Configure was needed to attached the output (TIOA6 in my case)

The following scotch works - and outputs a lovely 3Mhz signal - I thing I am missing something however.

Using timer 1, RA increments every sysclk/2 ticks = 42,000,000

I toggle the output every ??? 2 TIMER1 ticks (when RA = RC) so I assume I should be getting a 21mhz wave - any ideas anyone?


void TC6_Handler()
        TC_GetStatus(TC2, 0);


void startTimer(Tc *tc, uint32_t channel, IRQn_Type irq) {
        TC_Configure(tc, channel,
               TC_CMR_WAVE |
               TC_CMR_WAVSEL_UP_RC |
               TC_CMR_ACPA_TOGGLE );  // RC compare TOGGLES TIOA););

        TC_SetRA(tc, channel, 1); //50% high, 50% low
        TC_SetRC(tc, channel, 1);
         TC_Start(tc, channel);


void setup(){

        startTimer(TC2, 0, TC6_IRQn);

void loop(){

FWIW - it appears that getting anying above a stable 3Mhz signal is a bit iffy at most.

Have spent best part of 2 weeks on this (hour or 2 at a time) but have now ordered an external clock generator (Adafruit).

Anyway, with minor mods, if anyone wants a 3Mhz signal, with minor mods (just to clean it up), the above code will do it (BTW it is a sketch not a scotch.....)




Maybe somene can help me with my problem
How to correctly set up registers.

What I want to do.
I want to set up timer and to get it triggered not only when it reaches some redefined value OR on a external signal with for falling edge . What I did now and what I want to get rid of (I dont want to use attachinterrupt, I want to use TC handler, but for this I have to set up TIOB, PIO? and TC_CMR0?) :smiley-eek:

setup code:   
attachInterrupt(22, inter_test, FALLING);
TC_Start(TC0, 0);
   void inter_test()
   Serial.println(TC_ReadCV(TC0, 0)); //read ticks
   TC0->TC_BCR = TC_BCR_SYNC; //reset timer


Sep 02, 2014, 08:40 pm Last Edit: Sep 02, 2014, 08:52 pm by interrupt Reason: 1

I have read manual and I tried to make setup code, it is not working yet.

In manual I see:
The channel can also be configured to have an external trigger. In Waveform Mode, an external event can be programmed on one of the following signals: TIOB, XC0, XC1 or XC2. This external event can then be programmed to perform a trigger by setting ENETRG in TC_CMR.
If an external trigger is used, the duration of the pulses must be longer than the master clock period in order to be detected.
In Waveform Mode, TIOA is always configured to be an output and TIOB is an output if it is not selected to be the external trigger

My problem was:
* I want to use TC0, channel 0
* I think I will use Waveform mode, without RC compare
* I want to use interrupts - interrupt should be triggered on external event (signal from other device of FALLING edge, 50Hz)
* I want to use interrupt handler

Code: [Select]

void setup()
 pinMode(22, INPUT); //I dont know, do I have to set it up just like that, I want to use pin22 as external signal

 pmc_set_writeprotect(false); //For being able to set up TC registers (like TC_CMR, TC_CCR etc)

 TC_Configure(TC0, 0, 0b00000000000000001001001000000000); // From manual (explained below)
 TC0->TC_CHANNEL[0].TC_CCR = TC_CCR_CLKEN | TC_CCR_SWTRG; //Start TC or use APIs TC_start function

 //TC0->TC_CHANNEL[0].TC_IER = 0b00000000000000000000000010000001; // IER = interrupt enable register
 TC0->TC_CHANNEL[0].TC_IER = TC_IER_ETRGS | TC_IER_COVFS; //Enable interupt

void loop()
 Serial.println(TC_ReadCV(TC0, 0));

void TC0_Handler()
 Serial.println(TC_ReadCV(TC0, 0));

So problem here is
This code is never handled in TC0_Handler, even, when counter gets full.

1) Is interrupt handler set up correctly?
2) How do I tell the system that I use pin22 (B.26) as an input for TIOB (Do I have to set up PIO registers, how)?
3) Maybe TC_CMR mode is set up incorrectly?:
Code: [Select]
TC_Configure(TC0, 0, 0b00000000000000001001001000000000);

I got it like this:
TC_CMR register, using Waveform Mode. This mode is used in TC_Configure().
TCCLKS: 000  -> usage of MCK/2 ie 48Mhz
CLKI: 0 ehk counter is incremtented on rising edge of the clock - fine by me
BURST: 00 - the clock is not gated by an external signal - fine by me
CPCSTOP: 0 counter clock is not stopped when counter reaches RC? I think its correct, I dont use RC, in waveform mode 00.
CPCDIS: 0 - counter clock is not disabled when counter reaches RC - I think its OK like this.
EEVTEDG: 10 (2) - on falling egde of external event triggers - This is correct I suppose.
EEVT: 00 - TIOB, signal selected as external event - Must be like that, according to manual.
ENETRG: 1 - the external event restars the counter and starts the coutner clock - Yup.
WAVSEL: 00 - upmode without automatic trigger on RC compare - I think its OK, I cant use here RC compare. 00 is OK.
WAVE: 1 - waveform is enabled
ACPA: 00 - ra compare effect on TIOA - none - as I dont use RA compare
ACPC: 00 - rc compare effect on TIOA - none - as I dont use RC compare
AEEVT: 00 - external event effet on TIOA???? Hmmm, what's that?
ASWTRG: 00 stoftware trigger effect on TIOA - Hmmmm, what's that?
BCPS, BCPC, 00 00 - ???
BEEVT, BSWTRG: 00 00 - ????

Are you to able to explain the requirements a little more;

If for example you want a single shot, you may want to steer clear of timers and just put some code like what follows;

volatile fred int;

ISR() {
   long ct;
  ** Now register ISR as a falling edge interrupt on a pin - exercise for the reader ***
  while (fred==0)
     if (millis() > (ct + 1000))

Disengage interupt code

*** Now do something


In theory, either a second will go by or via the ISR the volatile variable fred gets set to break out of the loop

SO this is a single shot  and you can evaluate fred - if it has value 1, you know the timer expired - if 2 you know the interrupt fired.

I suspect however you want to do something more than just a single shot - in which case perhaps you could take the code in loop and put it into another routine - and call it each time you want to check for an interrupt in a period of time.



I'm working on something similar, if i have a success, be sure i'll post something relevant. If you suceed what you are doing, pls post over here.



how can i produce a
rectangle signal (250KHz) with arduino due.


Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131