STM32F401RE Nucleo failing to read DHT22 sensor

Question

This is my first project and I am trying to read the temperature readings from a DHT22 sensor using a STM32F401RE-NUCLEO board.

My code is failing at reading the input from the DHT22 sensor when I use the CCR1 command. I have verified my circuit is working as I previously tested it using the MBED compiler.

I set up the timer to use TIM_CHANNEL_1 and TIM3 instance, which according to the STM32CubeMX GUI corresponds to STM32 pin PA6.

My DHT22 structure looks like the following:

typedef struct{
    uint8_t             bitsRX[5];
    float               temp;
    float               hum;
    uint8_t             crcErrorFlag;
    DHT22_STATE         state;
    TIM_HandleTypeDef   timHandle;
    TIM_IC_InitTypeDef  timICHandle;
    uint32_t            timChannel;
    uint16_t            gpioPin;
    GPIO_TypeDef*       gpioPort;
    int                 bitPos;
    IRQn_Type           timerIRQn;
    uint32_t            gpioAlternateFunction;
    uint16_t            lastVal;
    void                (*errorCallback)(DHT22_RESULT);
}

I set up my DHT object as the following:

dht.gpioPin = GPIO_PIN_6;
dht.gpioPort = GPIOA;
dht.timChannel = TIM_CHANNEL_1;
dht.gpioAlternateFunction = GPIO_AF2_TIM3;
dht.timHandle.Instance = TIM3;

I am running the following command to try and capture the value:

uint16_t val = HAL_TIM_ReadCapturedValue(&dht->timHandle, dht->timChannel);

Where the function is defined as the following (snipped off the later parts since I only care about channel 1):

uint32_t HAL_TIM_ReadCapturedValue(TIM_HandleTypeDef *htim, uint32_t Channel)
{
uint32_t tmpreg = 0U;

__HAL_LOCK(htim);
switch (Channel)
{
case TIM_CHANNEL_1:
{
  /* Check the parameters */
  assert_param(IS_TIM_CC1_INSTANCE(htim->Instance));
  /* Return the capture 1 value */

  tmpreg = htim->Instance->CCR1; // This line is giving me the problem

  break;
}

The tmpreg = htim->Instance->CCR1 is always returning 0.

Any solutions or pointers that may help me?

Answer 1

In cases like these keep the following points in mind:

1. Haven't used on MBED but use a debugging tool like OpenOCD bundled with gdb and try to debug the code while looking at the input registers. In eclipse you can do it with a tool like EmbSysRegisters. Google for some tutorials and you'll save a lot of time.
2. Looking at the datasheet of DHT22, it says it needs a MCU to sensor signal to initiate the process. Have you checked that?