Use case #1

In this use case, the PWM module is configured to:

• Output a square wave on PWM channel 0
• The frequency of the square wave is 1KHz
• The duty cycle is changed in the PWM ISR
• Clock A as the source clock
• The output wave can be checked on the selected output pin

Setup steps

Prerequisites

• Power Management Controller driver
• General Purpose I/O Management (gpio)

Example code

Add to application C-file:

pwm_channel_t pwm_channel_instance;

void PWM_Handler(void)
{
    static uint32_t ul_duty = 0;
    uint32_t ul_status;
    static uint8_t uc_countn = 0;
    static uint8_t uc_flag = 1;
 
    ul_status = pwm_channel_get_interrupt_status(PWM);
    if ((ul_status & PWM_CHANNEL_0) == PWM_CHANNEL_0) {
        uc_count++;
        if (uc_count == 10) {
            if (uc_flag) {
                ul_duty++;
                if (ul_duty == 100) {
                    uc_flag = 0;
                }
            } else {
                ul_duty--;
                if (ul_duty == 0) {
                    uc_flag = 1;
                }
            }
            uc_count = 0;
            pwm_channel_instance.channel = PWM_CHANNEL_0;
            pwm_channel_update_duty(PWM, &pwm_channel_instance, ul_duty);
        }
    }
}

pmc_enable_periph_clk(ID_PWM);
 
pwm_channel_disable(PWM, PWM_CHANNEL_0);
 
pwm_clock_t clock_setting = {
    .ul_clka = 1000 * 100,
    .ul_clkb = 0,
    .ul_mck = 48000000
};
pwm_init(PWM, &clock_setting);
 
pwm_channel_instance.ul_prescaler = PWM_CMR_CPRE_CLKA;
pwm_channel_instance.ul_period = 100;
pwm_channel_instance.ul_duty = 0;
pwm_channel_instance.channel = PWM_CHANNEL_0;
pwm_channel_init(PWM, &pwm_channel_instance);
 
pwm_channel_enable_interrupt(PWM, PWM_CHANNEL_0, 0);

Workflow

1. Define the PWM channel instance in order to configure channel 0:

   • pwm_channel_t pwm_channel_instance; 

2. Define the PWM interrupt handler in the application:

   • void PWM_Handler(void); 

3. In PWM_Handler(), get PWM interrupt status:

   • ul_status = pwm_channel_get_interrupt_status(PWM); 

4. In PWM_Handler(), check whether the PWM channel 0 interrupt has occurred:

   • if ((ul_status & PWM_CHANNEL_0) == PWM_CHANNEL_0) {
     }

5. In PWM_Handler(), if the PWM channel 0 interrupt has occurred, update the ul_duty value:

   • uc_count++;
     if (uc_count == 10) {
         if (uc_flag) {
             ul_duty++;
             if (ul_duty >= 100) {
                 uc_flag = 0;
             }
         } else {
             ul_duty--;
             if (ul_duty == 0) {
                 uc_flag = 1;
             }
         }
     }

6. In PWM_Handler(), if the ul_duty value has been updated, change the square wave duty:

   • pwm_channel_instance.channel = PWM_CHANNEL_0;
     pwm_channel_update_duty(PWM, &pwm_channel_instance, ul_duty);

7. Enable the PWM clock:

   • pmc_enable_periph_clk(ID_PWM); 

8. Disable PWM channel 0:

   • pwm_channel_disable(PWM, PWM_CHANNEL_0); 

9. Setup clock for PWM module:

   • pwm_clock_t clock_setting = {
         .ul_clka = 1000 * 100,
         .ul_clkb = 0,
         .ul_mck = 48000000
     };
     pwm_init(PWM, &clock_setting);

   • Note

     1. Only Clock A is configured (clock B is not used).

1. The expected frequency is 1KHz, system main clock is assumed to be 48Mhz.
2. Initialize channel instance and configure PWM channel 0, selecting clock A as its source clock and setting the initial ducy as 0%:

   • pwm_channel_instance.ul_prescaler = PWM_CMR_CPRE_CLKA;
     pwm_channel_instance.ul_period = 100;
     pwm_channel_instance.ul_duty = 0;
     pwm_channel_instance.channel = PWM_CHANNEL_0;
     pwm_channel_init(PWM, &pwm_channel_instance);

   • Note

     1. Period is left-aligned and output waveform starts at a low level.

1. The pwm_channel_instance can be re-used to configure other PWM channels after setting the required parameters.
2. Enable channel 0 interrupt:

   • pwm_channel_enable_interrupt(PWM, PWM_CHANNEL_0, 0); 

   • Note

     1.In order to enable the PWM interrupt, the NVIC must be configured to enable the PWM interrupt. 2. When the channel 0 counter reaches the channel period, the interrupt (counter event) will occur.

Usage steps

Example code

pwm_channel_enable(PWM, PWM_CHANNEL_0);

Workflow

1. Enable PWM channel 0 and output square wave on this channel:

   • pwm_channel_enable(PWM, PWM_CHANNEL_0);