CCS/TM4C123GH6PM: Issues Using TivaWare PWM Example

In the posted code of the PWM0_init() function there are no calls to GPIOPinTypePWM(). Calls to GPIOPinTypePWM() is required to place the pins under hardware control.

Is GPIOPinTypePWM() called else-ware in the code for the PB6 and PB7 pins?

Chester,

Thanks for pointing that out. That was not previously included int he code. I added in a call to GPIOPinTypePWM but I still don't get any output. This is what the revised code looks like:

void PWM0_init(void){
////////////////////////////////////////////////////////

//
// Enable the PWM0 peripheral
//

SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
//

// Wait for the PWM0 module to be ready.
//
while(!SysCtlPeripheralReady(SYSCTL_PERIPH_PWM0))
{
}
//
// Configure the PWM generator for count down mode with immediate updates
// to the parameters.
//

//Added to ensure PB6 and PB7 are ready to go...
GPIOPinTypePWM(GPIO_PORTB_BASE,GPIO_PIN_6|GPIO_PIN_7);


PWMGenConfigure(PWM0_BASE, PWM_GEN_0,
PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
//
// Set the period. For a 50 KHz frequency, the period = 1/50,000, or 20
// microseconds. For a 20 MHz clock, this translates to 400 clock ticks.
// Use this value to set the period.
//
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 400);
//
// Set the pulse width of PWM0 for a 25% duty cycle.
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0, 100);
//
// Set the pulse width of PWM1 for a 75% duty cycle.
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_1, 300);



//
// Start the timers in generator 0.
//
PWMGenEnable(PWM0_BASE, PWM_GEN_0);
//
// Enable the outputs.
//
PWMOutputState(PWM0_BASE, (PWM_OUT_0_BIT | PWM_OUT_1_BIT), true);


/////////////////////////////////////////////////////////////////////
}

Let me know if that looks right or if you have any other theories.

Thanks,
Jim

Jim Carucci said:

Let me know if that looks right or if you have any other theories.

Comparing the above code against TivaWare PWM examples shows your PWM0_init() function is missing calls to GPIOPinConfigure() to set the pin muxing for the PWM pins.

Try adding the following before the call to GPIOPinTypePWM():

    GPIOPinConfigure(GPIO_PB6_M0PWM0);
    GPIOPinConfigure(GPIO_PB7_M0PWM1);

Chester,

Another good suggestion but sadly, I still get no output to either PB6 or PB7 on the oscilloscope when I attempt to run the following revised code:

void PWM0_init(void){
////////////////////////////////////////////////////////

//
// Enable the PWM0 peripheral
//

SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
//

// Wait for the PWM0 module to be ready.
//
while(!SysCtlPeripheralReady(SYSCTL_PERIPH_PWM0))
{
}
//
// Configure the PWM generator for count down mode with immediate updates
// to the parameters.
//
//Configure PB6 and PB7 to PWM
GPIOPinConfigure(GPIO_PB6_M0PWM0);
GPIOPinConfigure(GPIO_PB7_M0PWM1);

//Added to ensure PB6 and PB7 are ready to go...
GPIOPinTypePWM(GPIO_PORTB_BASE,GPIO_PIN_6|GPIO_PIN_7);

PWMGenConfigure(PWM0_BASE, PWM_GEN_0,
PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
//
// Set the period. For a 50 KHz frequency, the period = 1/50,000, or 20
// microseconds. For a 20 MHz clock, this translates to 400 clock ticks.
// Use this value to set the period.
//
PWMGenPeriodSet(PWM0_BASE, PWM_GEN_0, 400);
//
// Set the pulse width of PWM0 for a 25% duty cycle.
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_0, 100);
//
// Set the pulse width of PWM1 for a 75% duty cycle.
//
PWMPulseWidthSet(PWM0_BASE, PWM_OUT_1, 300);

//
// Start the timers in generator 0.
//
PWMGenEnable(PWM0_BASE, PWM_GEN_0);
//
// Enable the outputs.
//
PWMOutputState(PWM0_BASE, (PWM_OUT_0_BIT | PWM_OUT_1_BIT), true);

/////////////////////////////////////////////////////////////////////
}

Any other theories or suggestions?

Hello Jim

Is the clock to GPIO Port B enabled?

I believe that was the problem. I am now getting a read on my scope after using SysCtlPeriphalEnable on port B. Thanks Amit and Chester for the quick responses!