No PWM Output on selected Timer Pin

Awesome, that helped a lot.

I also have been trying to play around with the values of the LoadSet and MatchSet. I was able to get a nice square wave a minute ago by putting the Match at half the Load, but now I can't seem to replicate that. I just keep getting skinny little pulses that are inaudible.

I'm pretty sure I understand how the timer system works -- you take the clock speed of the microcontroller and divide that by however many clock ticks you want the timer to run for and you work out the frequency that way. Then you take half of that value and load it into the MatchSet to create duty cycle. Of course 16-bit numbers only go to 32 768 so there's a limit to the frequencies available but it makes sense.

I don't know what I changed to make it stop producing nice square waves! Argh.

With the Load at 12000 (decimal) and the Match at 6000 I'm now getting pulses 48uS wide, 8mS apart.

Hi Aurelius,

Probably a code post would be useful.

Regards

Amit

As you can see, the only changes I've really made are to the numbers and also adding the split pair as you recommended.

#include <stdint.h>
#include <stdbool.h>
#include "utils/ustdlib.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/interrupt.h"
#include "driverlib/sysctl.h"
#include "driverlib/pin_map.h"
#include "driverlib/debug.h"
#include "driverlib/comp.h"
#include "driverlib/gpio.h"
#include "driverlib/timer.h"
#include "driverlib/hibernate.h"
#include "driverlib/rom.h"
#include "driverlib/rom_map.h"

void makeSomeNoise(uint32_t ui32currentTone) {

	ROM_TimerDisable(TIMER5_BASE, TIMER_A); // make sure timer is off

	if(ui32currentTone == 1)
	{
		// if you're with me!
		//ROM_TimerPrescaleSet(TIMER5_BASE, TIMER_A, 0x15);
		ROM_TimerLoadSet(TIMER5_BASE, TIMER_A, 8000);
		ROM_TimerMatchSet(TIMER5_BASE, TIMER_A, 500);

		ROM_TimerEnable(TIMER5_BASE, TIMER_A);
		ROM_SysCtlDelay(40000000);
		ROM_TimerDisable(TIMER5_BASE, TIMER_A);
	}
	if(ui32currentTone == 2)
	{
		//ROM_TimerPrescaleSet(TIMER5_BASE, TIMER_A, 0x10);
		ROM_TimerLoadSet(TIMER5_BASE, TIMER_A, 8000);
		ROM_TimerMatchSet(TIMER5_BASE, TIMER_A, 1000);

		ROM_TimerEnable(TIMER5_BASE, TIMER_A);
		ROM_SysCtlDelay(40000000);
		ROM_TimerDisable(TIMER5_BASE, TIMER_A);
	}
	if(ui32currentTone == 3)
	{
		// do nothing, because the sound has been cut
	}

}

void PWMInitialize(void)
{
	ROM_GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_4); // pin for enabling LM4819

	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER5); // enable timer5

	ROM_GPIOPinTypeTimer(GPIO_PORTB_BASE, GPIO_PIN_2);
	ROM_GPIOPinConfigure(GPIO_PB2_T5CCP0); // set PB2 as Timer5 output CCP0
	ROM_TimerClockSourceSet(TIMER5_BASE, TIMER_CLOCK_SYSTEM);
	//ROM_TimerPrescaleSet(TIMER5_BASE, TIMER_A, 0x10);
	ROM_TimerConfigure(TIMER5_BASE, TIMER_CFG_A_PWM|TIMER_CFG_SPLIT_PAIR); // configure timer for half-width PWM

	ROM_GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_4, 0x05); // PD4 goes high to activate LM4819 amp
}

void Comp0IntHandler(void)
{
	ROM_GPIOPinWrite(GPIO_PORTQ_BASE, GPIO_PIN_7, 0x80); // turn led on

	ROM_SysCtlDelay(40000000);
	makeSomeNoise(1); // play tone 1
	//ROM_SysCtlDelay(4000000);
	//makeSomeNoise(2); // play tone 2
	//ROM_SysCtlDelay(40000000);
	//makeSomeNoise(3); // shut off sounds

	ROM_GPIOPinWrite(GPIO_PORTQ_BASE, GPIO_PIN_7, 0x00); // turn led off
	ROM_ComparatorIntClear(COMP_BASE, 0);
}

int main(void) {

	ROM_SysCtlClockFreqSet(SYSCTL_OSC_INT|SYSCTL_USE_PLL|SYSCTL_CFG_VCO_480, 120000000); // set system clock to 120MHz

	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD); // enable port D
	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOQ); // enable port Q
	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOC); // enable port C
	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB); // enable port B
	ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_COMP0); // enable analog comparator 0

	PWMInitialize(); // initalize PWM system

	ROM_GPIOPinTypeGPIOOutput(GPIO_PORTQ_BASE, GPIO_PIN_7); // set PQ4 to output (Blue LED)
	ROM_GPIOPinWrite(GPIO_PORTQ_BASE, GPIO_PIN_7, 0x00); // ensure blue LED is off

	ROM_GPIOPinTypeComparator(GPIO_PORTC_BASE, GPIO_PIN_7);
	ROM_GPIOPinTypeComparator(GPIO_PORTC_BASE, GPIO_PIN_6);

	ROM_ComparatorRefSet(COMP_BASE, COMP_REF_2_0625V); // set reference to 2.0625V
	ROM_ComparatorConfigure(COMP_BASE, 0, (COMP_TRIG_NONE|COMP_INT_BOTH|COMP_ASRCP_REF|COMP_OUTPUT_NORMAL)); // configure COMP0
	ComparatorIntRegister(COMP_BASE, 0, Comp0IntHandler);
	ROM_ComparatorIntEnable(COMP_BASE, 0);

	while(1)
	{
		// twiddle thumbs
	}
}

Hello Aurelius,

Looks like the disabling of the timer in the if-else statement in the makeSomeNoise function. I assume removing that will help. Also with the load and match of 8000 and 500, you would get pulses of 6.25% Duty Cycle.

Regards

Amit

Yeah but even when I play with the numbers and use 8000 and 4000 I'm still getting tiny little pulses.

I'll try cutting the TimerDisable and see if that helps.

EDIT: I remembered that for some reason variables stay in the memory unless you do a full reset. So if you reprogram the chip and didn't clear the prescaler before, it stays on the new program. Talk about a huge bug!!! so a full reset and reprogram fixed it...

Hi Aurelius.

You mean to say the prescaler configured in the timer?

Regards

Amit