CCS/F28M35H52C: Wrong timing for a 32-bit timer count decrement

Anoja,

Please double check the source clock values and divide settings.  It looks like you are off by a factor of 3.  For reference, please see lab 2 in the F28M35 workshop:

https://training.ti.com/c2000-f28m35x-microcontroller-workshop?cu=1137791

Also, please see the timer example in controlSUITE at:

C:\ti\controlSUITE\device_support\f28m35x\v220\F28M35x_examples_Master

I hope this helps. If this answers your question, please click the green "Verified Answer" button. Thanks.

- Ken

Hi Ken,

   The example at  C:\ti\controlSUITE\device_support\f28m35x\v220\F28M35x_examples_Master uses timer interrupt. What I want is to run timer in background and read the TAR register when required.

Here is my settings:

   // Disable the timers.
    HWREG(TIMER0_BASE + TIMER_O_CTL) &= ~(TIMER_CTL_TAEN | TIMER_CTL_TBEN);

    // Clean timer configuration register - 32bit configuration
    HWREG(TIMER0_BASE + TIMER_O_CFG) = 0x00;

    //Configure mode register - periodic
    HWREG(TIMER0_BASE + TIMER_O_TAMR) = 0x02;

    // Load start value
    HWREG(TIMER0_BASE + TIMER_O_TAILR) =  0xFFFFFFFF;

    // Enable the timer module.
    HWREG(TIMER0_BASE + TIMER_O_CTL) |= (TIMER_CTL_TAEN | TIMER_CTL_TBEN);

 The clock setting I used is

// Setup main clock tree for 75MHz - M3 and 150MHz - C28x
SysCtlClockConfigSet(SYSCTL_USE_PLL | (SYSCTL_SPLLIMULT_M & 0xF) |
SYSCTL_SYSDIV_1 | SYSCTL_M3SSDIV_2 | SYSCTL_XCLKDIV_4);

This is what I am unsure of. In a while loop, I am polling when the load value goes to 0. Can you tell me if there is another way to test the count decrement of timer?

    while(1)
    {
        unsigned long loadValue = HWREG(TIMER0_BASE + TIMER_O_TAR);
        if(!loadValue)
        {
            GPIOPinWrite(GPIO_PORTC_BASE,GPIO_PIN_6,~GPIOPinRead(GPIO_PORTC_BASE, GPIO_PIN_6)); 
        }
    }

Anoja,

The issue is you are using the timer in periodic mode:

//Configure mode register - periodic

This means when counter expires on next cycle it will restart and checking the value of 0x0 in TAR register is not deterministic:

Therefore, by the time you read the value, the counter may have restarted again. It would be best to use interrupts or read the interrupt status register instead of the value or use one-shot mode instead of periodic mode.

This should explain the issue you are experiencing.  If this answers your question, please click the green "Verified Answer" button. Thanks.

- Ken