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STM32L151: Timer Capture Input (TIMx_CHy vs TIMx_ICy)

Question asked by Rehfinger.Thomas on Jun 23, 2014
Latest reply on Jul 23, 2014 by waclawek.jan

I'm using a STM32L151 and would like to connect the pin PA2 to one of the timer capture inputs. According to the reference manual and the example InputCaptureRouting in the STM32L1xx_StdPeriph_Lib_V1.1.1, this code should do the trick:

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2 | RCC_APB1Periph_COMP | RCC_APB1Periph_PWR, ENABLE);

    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_2;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_OD;
    GPIO_InitStructure.GPIO_PuPd  = 0;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

#if 1
    // Route PA2 to TIM2_IC3
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_RI);
    SYSCFG_RITIMInputCaptureConfig(RI_InputCapture_IC3, RI_InputCaptureRouting_0/*0: PA2*/);
    // Use PA2 as TIM2_CH3
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_TIM2);

    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    TIM_TimeBaseStructure.TIM_Period = 65535;
    TIM_TimeBaseStructure.TIM_Prescaler = (uint16_t)(SystemCoreClock/*Hz*/ / 100000/*10us/s*/) - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = 0;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    // Use TIM2_IC3 as Input Capture
    TIM_ICInitTypeDef  TIM_ICInitStructure;
    TIM_ICInitStructure.TIM_Channel     = TIM_Channel_3;
    TIM_ICInitStructure.TIM_ICPolarity  = TIM_ICPolarity_Rising;
    TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
    TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
    TIM_ICInitStructure.TIM_ICFilter    = 3;   // Filter: 8 clocks
    TIM_ICInit(TIM2, &TIM_ICInitStructure);
    TIM_Cmd(TIM2, ENABLE);

This should connect the pin PA2 to the Timer Capture Input TIM2_IC3. I would expect that pin PA2 is in a high impedance state in this case, but on a scope it is easy to see that it is driven low by the STM32.

If I change the #if 1 in the snippet above to #if 0, everything works as expected: PA2 is in high impedance state and a rising edge captures TIM2_CNT in register TIM2_CCR3.

Actually, I need to use PA10 as a Timer Capture Input which is only possible if it's routed via the RI module. I assumed that (if correctly configured) the TIMx_ICy signals are equivalent to the according TIMx_CHy signals. Is this correct (the documentation is not 100% clear in this point)?