/* pwm set up */ /* Compute the prescaler value */ PrescalerValue = (uint16_t) (

Question

/* pwm set up */


/* Compute the prescaler value */
PrescalerValue = (uint16_t) ((SystemCoreClock /2) / 21000000) - 1;


/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 665;
TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;


TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);


/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;


TIM_OC1Init(TIM4, &TIM_OCInitStructure);


TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);


/* PWM1 Mode configuration: Channel2 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC2Init(TIM4, &TIM_OCInitStructure);


TIM_OC2PreloadConfig(TIM4, TIM_OCPreload_Enable);


/* PWM1 Mode configuration: Channel3 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC3Init(TIM4, &TIM_OCInitStructure);


TIM_OC3PreloadConfig(TIM4, TIM_OCPreload_Enable);


/* PWM1 Mode configuration: Channel4 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC4Init(TIM4, &TIM_OCInitStructure);


TIM_OC4PreloadConfig(TIM4, TIM_OCPreload_Enable);


TIM_ARRPreloadConfig(TIM4, ENABLE);


/* TIM4 enable counter */
TIM_Cmd(TIM4, ENABLE);
/* DEMO */

int brightness = 0;


while(1) // Do not exit
{
brightness++;


TIM4->CCR3 = 333 - (brightness + 0) % 333; // set brightness
TIM4->CCR4 = 333 - (brightness + 166/2) % 333; // set brightness
TIM4->CCR1 = 333 - (brightness + 333/2) % 333; // set brightness
TIM4->CCR2 = 333 - (brightness + 499/2) % 333; // set brightness


for(i=0;i<10000;i++); // delay
for(i=0;i<10000;i++); // delay
for(i=0;i<10000;i++); // delay
}
}

Explanation / Answer

int main(void) // main program
{ TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
// Time base structure abd Time Output Compare structure defined
/* TIM config */

GPIO_InitTypeDef GPIO_InitStructure;

// GPIO init structure initialised

/* TIM4 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);

// Timer 4 on clock peripheral enabled


/* LEDs are on GPIOD */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
// GPIO on Port D enabled  
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15; // pin 12, 13, 14, 15 on PortD initialised for LED blinking

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; // alternate function mode
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz; // 100 MHZ blinking freuency
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ; // Pulled Up

// upto this point all the above were setting up output configurations on PORTD for GPIO
GPIO_Init(GPIOD, &GPIO_InitStructure); // calling all the initialisations


GPIO_PinAFConfig(GPIOD, GPIO_PinSource12, GPIO_AF_TIM4); // setting up PWMs on specified pins
GPIO_PinAFConfig(GPIOD, GPIO_PinSource13, GPIO_AF_TIM4); // setting up PWMs on specified pins
GPIO_PinAFConfig(GPIOD, GPIO_PinSource14, GPIO_AF_TIM4); // setting up PWMs on specified pins
GPIO_PinAFConfig(GPIOD, GPIO_PinSource15, GPIO_AF_TIM4); // setting up PWMs on specified pins

/* pwm set up */


/* Compute the prescaler value */
PrescalerValue = (uint16_t) ((SystemCoreClock /2) / 21000000) - 1;

// defined prescalar value on clock speed


/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 665; // set time period of TIME BASE
TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue; // set prescalar value on Time Base
TIM_TimeBaseStructure.TIM_ClockDivision = 0; // no clocj division
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; // count up
// configuarations fr TIMEBASE 4

TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure); // Configurations applied


/* PWM1 Mode configuration: Channel1 */ // PWM1 channel 1 configurations being changed
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;


TIM_OC1Init(TIM4, &TIM_OCInitStructure); // PWM1 used for output compare 1 on pin 12


TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);

// Similar processes repeated for output compare 2, 3 and 4 for pin 13, 14, 15 respectively
/* PWM1 Mode configuration: Channel2 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC2Init(TIM4, &TIM_OCInitStructure);


TIM_OC2PreloadConfig(TIM4, TIM_OCPreload_Enable);


/* PWM1 Mode configuration: Channel3 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC3Init(TIM4, &TIM_OCInitStructure);


TIM_OC3PreloadConfig(TIM4, TIM_OCPreload_Enable);


/* PWM1 Mode configuration: Channel4 */
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0;


TIM_OC4Init(TIM4, &TIM_OCInitStructure);


TIM_OC4PreloadConfig(TIM4, TIM_OCPreload_Enable);


TIM_ARRPreloadConfig(TIM4, ENABLE);// reloaded timer 4 counter configuration


/* TIM4 enable counter */
TIM_Cmd(TIM4, ENABLE);
/* DEMO */

int brightness = 0; // initial brightness 0


while(1) // Do not exit
{
brightness++;


TIM4->CCR3 = 333 - (brightness + 0) % 333; // set brightness
TIM4->CCR4 = 333 - (brightness + 166/2) % 333; // set brightness
TIM4->CCR1 = 333 - (brightness + 333/2) % 333; // set brightness
TIM4->CCR2 = 333 - (brightness + 499/2) % 333; // set brightness


for(i=0;i<10000;i++); // delay
for(i=0;i<10000;i++); // delay
for(i=0;i<10000;i++); // delay
}
}

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