STM32F2 Counting pulses using ETR and generating one pulse at max speed

Posted on February 27, 2015 at 08:20

Hi.

To start i'm using STM32F207

I have a 15Mhz signal (that sometimes is enabled and sometimes it is not) connected to TIM3 ETR. I just want to count pulses and generate a pulse after few of this clocks (from 1 to 16 configured by software).

To try it, I have set the TIM3 ETR (PD2 pin) as clock for TIMER 3, and it works (it starts counting). The code used is:

  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;

  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

  GPIO_Init(GPIOD, &GPIO_InitStructure);

  GPIO_PinAFConfig(GPIOD, GPIO_PinSource2, GPIO_AF_TIM3);  

  TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_External1);

  TIM_SelectInputTrigger(TIM3,TIM_TS_ETRF);

  TIM_ETRClockMode2Config(TIM3,TIM_ExtTRGPSC_OFF, TIM_ExtTRGPolarity_NonInverted, 0);

  TIM_TIxExternalClockConfig (TIM3, TIM_TIxExternalCLK1Source_TI2, TIM_ICPolarity_Falling, 0) ;

This is working ok as I said. Now I want to make a pulse faster than TIM3 clock if possible. Configuring TIM3 to count up from 0 to the current count limit

  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

  TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;        

  TIM_TimeBaseStructure.TIM_CounterMode   = TIM_CounterMode_Up;  

  TIM_TimeBaseStructure.TIM_Period        = 3;            //Count limit

  TIM_TimeBaseStructure.TIM_Prescaler     = 0;                   

  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);                

And now I have to set the output. I would like a pulse, so i tried the One-Pulse thing, but it is not working or not working as I wished. I have tried with PWM1/2 and Toggle. It counts right, but toggle is not ok since it generates a ''clock divider'', and pwm generates pulses at speed of the clock and thats not ok.

I would need a small delay between the detection of the counting event and the rising of the output. This is what i tried:

  TIM_OCInitTypeDef       TIM3_OC; 

  TIM3_OC.TIM_OCMode      = TIM_OCMode_PWM1;             

  TIM3_OC.TIM_OutputState = TIM_OutputState_Enable;      

  TIM3_OC.TIM_OCPolarity  = TIM_OCPolarity_High;         

  TIM3_OC.TIM_Pulse       = 1;                           

  TIM_OC3Init(TIM3, &TIM3_OC);                           

  TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);      

  TIM_SelectOnePulseMode(TIM3,TIM_OPMode_Repetitive);

  TIM_SelectInputTrigger(TIM3, TIM_TS_TI2FP2);

In the image attached I explain what to I get and what do I need. 

I have seen a card done by another company using STM32F207, and same pins (PD2 clk input, PC7 pulse output and PC8 pulse output). Any idea or help would be welcomed.

Thanks in advance

#timers #pwm-tim3 #one-pulse