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PIC32 delay help

sanyika95

Hello everyone!

 

I just started to learn PIC32 programming with a PIC32 Ethernet Starter kit. I wanted to blink its led, 1 second on - 1 second off.

 

Here is the code for the delay:

#define USHORT unsigned short

void delayMs(USHORT milisec) {
    T1CON = 0x8010;
    TMR1 = 0x00;
    USHORT i = 0;
    PR1 = 0x40;
    while(i != milisec) {
        while(TMR1) {
        }
        i++;
        TMR1 = 0x00;
    }
    T1CON = 0x00;
    return;
}

 

It just works (or it looks like to work, I haven't measured it with an oscilloscope, just with a "stopwatch") and I don't know why. Can someone explain me?

 

 

The datasheet of the kit:

http://ww1.microchip.com/downloads/en/DeviceDoc/61166A.pdf

 

The datasheet of its PIC:

http://ww1.microchip.com/downloads/en/devicedoc/60001156j.pdf

Parents

  • I am not familiar with the PIC32 but that is strange code.  You need to know what the clock speed is and how the dividers to the timer are set.  A quick look at the datasheet shows that T1CON is the timer control register for TIMER1.  It looks like the variable milisec holds the value 1000 and that the register TMR1 is incremented once per millisecond and then the while will loop 1000 times using the variable i as a counter.  Of course normally you would have the timer count to the specified number of milliseconds and trigger an interrupt without blocking.

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  • I am not familiar with the PIC32 but that is strange code.  You need to know what the clock speed is and how the dividers to the timer are set.  A quick look at the datasheet shows that T1CON is the timer control register for TIMER1.  It looks like the variable milisec holds the value 1000 and that the register TMR1 is incremented once per millisecond and then the while will loop 1000 times using the variable i as a counter.  Of course normally you would have the timer count to the specified number of milliseconds and trigger an interrupt without blocking.

Children
  • in reply to fmilburn

    I don't really know the clock speed. In the datasheets there were a 32kHz and a 8MHz clock as internal. I did my calculation with both of them and none of them worked.

     

    As you said, the T1CON is the control register of TIMER1. In the code, the T1CON is set to Enable timer, set its prescaler to 8 and use the internal clock.

     

    You wrote the TMR1 is incremented once per milisecond, but if I understood the timing well, the TMR1 register will increase at every hit of the clock! So it have to reach X bit, depending on the clock and the prescaler to wait 1 milisecond. The PR1 is the value when to reset the TMR1.

    So when the TMR1 reaches 64 (in decimal) is 1 milisecond.

     

    The question is to understand the math behind it to be able to reproduce it on other MCU-s, with different clock speed and prescaler.

  • in reply to sanyika95

    I would not want to reproduce that code on another MCU regardless of clock speed and prescalar settings :-).  It is straight forward to track milliseconds on the microcontrollers I am familiar with - set the timer to count up and when it reaches 1 millisecond trigger an interrupt that increments the millisecond counter in an ISR.  Of course you must know how to set the clocks and timers to do this and the code you are working from does not seem to do this in a very clear manner.  Suggest finding a better example as suggested below....