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using prescalar

mahavir dwivedi
Intellectual 370 points


hi,i am trying to toggle my led state after every 1 second....for this purpose i m using my timer1 in 16 bit mode Along with that i m using a prescalar of 255....but it's not working?

#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/sysctl.h"
#include "driverlib/interrupt.h"
#include "driverlib/gpio.h"
#include "driverlib/timer.h"

int main(void)
{
    
    /*Set the clocking to directly run from the crystal at 16MHz*/
    SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1);
    GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1,0);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER1);
    TimerConfigure(TIMER1_BASE, TIMER_CFG_A_PERIODIC);
    TimerPrescaleSet(TIMER1_BASE,TIMER_A,254);

    //ulPeriod = (SysCtlClockGet() / 10) / 2;
    //TimerLoadSet(TIMER1_BASE, TIMER_A, ulPeriod -1);

    IntEnable(INT_TIMER1A);
    TimerIntEnable(TIMER1_BASE, TIMER_TIMA_TIMEOUT);
    IntMasterEnable();

    TimerEnable(TIMER1_BASE, TIMER_A);

    while(1)
    {
    }
}

void Timer1IntHandler(void)
{
    // Clear the timer interrupt
    TimerIntClear(TIMER1_BASE, TIMER_TIMA_TIMEOUT);
    
    GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1, GPIO_PIN_1);
        SysCtlDelay(SysCtlClockGet()/3);
    

}

  • 0
    Guru 117855 points

    You report use of a 16 bit timer & mated prescaler - and report the (always well detailed/helpful) "Not Working!"  (bet you that w/in 60 seconds I can come up with at least 5 illustrations of famed, "Not working...")  Thus - that  description, "Not Working" provides very little value...  In fact, "eats" time/effort of your helpers - but saved you time/effort!   (good that!)...  "Not working" may range from Program Faulted to minor irregularity in Timer Result Register - we're given no clue!

    Now - you hold your entire program, "hostage" to the proper functioning of multiple function calls and/or unclearly defined variables.  Can that be good - is it wise?  To illustrate:

    a) "TimerLoadSet(TIMER1_BASE, TIMER_A, ulPeriod -1);" now commented out - relies upon the correctness of ulPeriod - does it not?  What happens if ulPeriod bears an illegal/improper value?

    b) Critical variable, "ulPeriod = (SysCtlClockGet() / 10) / 2;" now also commented out - relies upon the correct functioning of, "SysCtlClockGet()" - does it not?  And - "SysCtlClockGet()" - under rebrandWare & with certain TM4C MCUs - has long been reported (here & elsewhere) to be error-prone.  Thus you've introduced another potential pitfall.  Is the slight ease/gain you (hopefully) earn from such "indirect methods" worth it?  Surely not at this place - this time!

    c) Our group prefers to, "positively disable any Timer" prior to its set-up/config.  (that's safest, best practice)  You "assume/hope/pray that the timer is disabled" - less than ideal.

    d) You title your post, "Using Prescaler" - yet KISS dictates that you get the basic timer working first - and then and only then "patch in" the Prescaler.   In that manner - you have a far better basis by which to, "blame the Prescaler!"  Perhaps you've done such - but we're not told.  Doing too much - w/out individual test/verify - is a ticket to lost sleep/morale.  Once both perform to "timed perfection" then you can "tweak in" precise values.  (and possibly add properly chosen variables & "known good" function calls...)

    Violating KISS is rarely good - hope that case has been well made here...

    (I've not made the time/effort for exhaustive code review (other than 2 critical code lines you've commented into oblivion - w/out explanation!) believe your "method of attack" is flawed - and provided justification (and work-arounds) for that assessment...)