Question
F0discovery PWM with external clock and trigger
Posted on November 13, 2012 at 17:38
I want to create a simple PWM implementation which uses an external clock source and is synchronised to a trigger pulse (one pulse per PWM period). I need at least three (ideally four) channels of output with different duty cycles but all synchronised.
I have started by using the TIM_PWM_Output example in the firmware package. This provides the four outputs I want. What I am unclear on is how to set up the external clock source and which pin should be used for that. The code uses TIM1. I see my first hurdle as using an external clock source, then I can try to add the external trigger. Here is my code as it looks copied from the TIM_PWM_Output example:#include ''stm32f0_discovery.h''
int Set_PWM_Period(int period);
int Set_PWM_Duty_Cycle(int duty_cycle_1, int duty_cycle_2, int duty_cycle_3, int duty_cycle_4);
int Synchronise_To_Row_Clock(void);
int TIM_Config(void);
int Set_PWM_Period(int period) {
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
uint16_t TimerPeriod = 0;
uint16_t Channel1Pulse = 0, Channel2Pulse = 0, Channel3Pulse = 0, Channel4Pulse = 0;
/* Compute the value to be set in ARR regiter to generate signal frequency at 57 Khz */
TimerPeriod = (SystemCoreClock / 17570 ) - 1;
TimerPeriod = period; //<-- ************************************************************************
/* Compute CCR1 value to generate a duty cycle at 50% for channel 1 */
Channel1Pulse = (uint16_t) (((uint32_t) 5 * (TimerPeriod - 1)) / 10);
/* Compute CCR2 value to generate a duty cycle at 5% for channel 2 */
Channel2Pulse = (uint16_t) (((uint32_t) 375 * (TimerPeriod - 1)) / 1000);
/* Compute CCR3 value to generate a duty cycle at 25% for channel 3 */
Channel3Pulse = (uint16_t) (((uint32_t) 25 * (TimerPeriod - 1)) / 100);
/* Compute CCR4 value to generate a duty cycle at 5% for channel 4 */
Channel4Pulse = (uint16_t) (((uint32_t) 125 * (TimerPeriod- 1)) / 1000);
/* TIM1 clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1 , ENABLE);
/* Time Base configuration */
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period = TimerPeriod;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
/* Channel 1, 2, 3 and 4 Configuration in PWM mode */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;
TIM_OCInitStructure.TIM_Pulse = Channel1Pulse;
TIM_OC1Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_Pulse = Channel2Pulse;
TIM_OC2Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_Pulse = Channel3Pulse;
TIM_OC3Init(TIM1, &TIM_OCInitStructure);
TIM_OCInitStructure.TIM_Pulse = Channel4Pulse;
TIM_OC4Init(TIM1, &TIM_OCInitStructure);
/* TIM1 counter enable */
TIM_Cmd(TIM1, ENABLE);
/* TIM1 Main Output Enable */
TIM_CtrlPWMOutputs(TIM1, ENABLE);
return 0;
}
int Set_PWM_Duty_Cycle(int duty_cycle_1, int duty_cycle_2, int duty_cycle_3, int duty_cycle_4) {
return 0;
}
int Synchronise_To_Trigger_Pulse(void) {
return 0;
}
/**
* @brief Configure the TIM1 Pins.
* @param None
* @retval None
*/
int TIM_Config(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* GPIOA Clocks enable */
RCC_AHBPeriphClockCmd( RCC_AHBPeriph_GPIOA, ENABLE);
/* GPIOA Configuration: Channel 1, 2, 3 and 4 as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_11;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource8, GPIO_AF_2);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_2);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_2);
GPIO_PinAFConfig(GPIOA, GPIO_PinSource11, GPIO_AF_2);
return 0;
}
int main(void) {
int PWM_period, PWM_duty_cycle;
TIM_Config();
PWM_period = 1000; //manual setting of PWM_period
Set_PWM_Period(PWM_period);
//PWM_duty_cycle_1 = 500; //manually set PWM_duty_cycle for test
//PWM_duty_cycle_2 = 375; //manually set PWM_duty_cycle for test
//PWM_duty_cycle_3 = 250; //manually set PWM_duty_cycle for test
//PWM_duty_cycle_4 = 125; //manually set PWM_duty_cycle for test
//Set_PWM_Duty_Cycle(PWM_duty_cycle_1, PWM_duty_cycle_2, PWM_duty_cycle_3, PWM_duty_cycle_4);
//Synchronise_To_Trigger_Pulse(); // trigger for sync
while(1);
} 