Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 5 of 5

Thread: Pushing the limits with timers and interrupts on the Teensy 4.0

  1. #1
    Junior Member
    Join Date
    Oct 2019
    Posts
    17

    Pushing the limits with timers and interrupts on the Teensy 4.0

    I have experimented with the general purpose timer (GPT) and am quite pleased with how it works (except the fact that reading from and writing to the status register takes incredibly long *ahem*). There are two entirely independent GPTs (GPT1 and GPT2) that offer three output-compare channels, two input capture channels (haven't tried those yet, there simply aren't enough pins for that on the Teensy). If you're interested in using the GPTs to execute your own interrupt service routines, I encourage you to read this thread: https://forum.pjrc.com/threads/58134...pare-interrupt

    But in some instances, two independent counters just aren't enough. Reading through the manual I found that there are almost countless of them (pun totally intended), but while there are some examples (like the ones for the periodic interrupt timer in section 52.6), there is nothing that points me to the all important part of how to attach my own isr to the compare event of the timer. For the GPT1 it looks something like this (leaving out the part about configuring the timer itself):

    Code:
    attachInterruptVector(IRQ_GPT1, myISR);	// Specify the isr you want to be executed
    					// (in this case that function is called myISR and is defined somewhere else)
    NVIC_ENABLE_IRQ(IRQ_GPT1);		// Enable the interrupt in the nested vectored interrupt controller table (NVIC)
    So my specific question is: How do I do this for the PIT?

    And more broadly: How can you do this for all the other timers that are available on the Teensy 4.0?

    Thanks!

  2. #2
    Senior Member
    Join Date
    Apr 2014
    Location
    Germany
    Posts
    1,057
    How can you do this for all the other timers that are available on the Teensy 4.0?
    The TeensyTimerTool might be interesting for you. https://github.com/luni64/TeensyTimerTool

  3. #3
    Junior Member
    Join Date
    Jul 2020
    Posts
    7
    I was checking out PIT recently on teensy 4.0.
    Although you can setup 4 different timers. It seems that you can use only one interrupt out of four PIT timers. you can change PIT_LDVALx = (Required time period * Timer Frequency) - 1.
    According to readings i got Timer Frequency is roughly 25Mhz.
    This is the code I used:
    Code:
    volatile uint32_t curr = 0, prev = 0;
    
    void setup() {
      Serial.begin(115200);
      PIT_SETUP();
    }
    
    void loop() {
    }
    
    void PIT_SETUP() {
      PIT_MCR = 0;  //Enable PIT
      PIT_LDVAL0 = 2499;// for 100 micro seconds
      PIT_TCTRL0 = PIT_TCTRL_TIE;// PIT Interrupt enable for Timer0
      PIT_TCTRL0 |= PIT_TCTRL_TEN;// start Timer0
      attachInterruptVector(IRQ_PIT, TIM0);// attach TIM0(isr) to Timer0 PIT interrupt
      NVIC_ENABLE_IRQ(IRQ_PIT);
    }
    
    inline void TIM0() {
      PIT_TFLG0 |= PIT_TFLG_TIF;// to enable interrupt again
      curr = micros();
      Serial.println(curr - prev);
      prev = curr;
    }

  4. #4
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    22,512
    Calling Serial.println() from this interrupt will probably work since you're not also using it from the main program. But generally it's a good idea to keep your interrupt code short and avoid calling complex functions.

  5. #5
    Junior Member
    Join Date
    Jul 2020
    Posts
    7
    Quote Originally Posted by PaulStoffregen View Post
    Calling Serial.println() from this interrupt will probably work since you're not also using it from the main program. But generally it's a good idea to keep your interrupt code short and avoid calling complex functions.
    Noted! thanks Paul.
    But It was just for debugging. So I guess that is okay.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •