ESP32-MCPWM_FrequencyMeter

ESP32 frequency Meter made with MCPWM Capture module.

• Tested with 1hz to 100khz, should work with higher values too.
• The time of measurement is near the period of the frequency measured.
• Have an aproximated +- 0,5% error. (with lower frequency it's even lower)

It uses the new method to use the MCPWM Capture, and not the deprecated one.

New Capture enable function:

esp_err_t mcpwm_capture_enable_channel(mcpwm_unit_t mcpwm_num, mcpwm_capture_channel_id_t cap_channel, const mcpwm_capture_config_t *cap_conf);

Deprecated Capture enable function: (Not used)

esp_err_t mcpwm_capture_enable(mcpwm_unit_t mcpwm_num, mcpwm_capture_signal_t cap_sig, mcpwm_capture_on_edge_t cap_edge, uint32_t num_of_pulse);

Setting MCPWM Capture:

• Config Object

Object type with all the capture configs. Pointed in enable function, to effectively configurate the channel. Notice that the inputs have some restrictions, these are listed below:

mcpwm_capture_config_t MCPWM_cap_config = { //Tha's my capture config, for example
  .cap_edge = MCPWM_POS_EDGE,               /*!<Set capture edge*/
  .cap_prescale = 1,                        /*!<Prescale of capture signal, ranging from 1 to 256 */
  .capture_cb = cap_ISR_cb,                 /*!<User defined capture event callback, running under interrupt context */
  .user_data = nullptr,                     /*!<User defined ISR callback function args*/
};

• The Input Values:

  • cap_edge: The Interrupt edge of the signal, in mcpwm_capture_on_edge_t type. Can be:

    • MCPWM_NEG_EDGE
    • MCPWM_POS_EDGE
    • MCPWM_BOTH_EDGE

  • cap_prescale: The preescale of the capture timer.

    • uint32_t 1 to 256

  • capture_cb: The callback function, which will be called every successful capture. Need to be in cap_isr_cb_t type, describe in the ISR section below.

  • user_data: A pointer with the user defined function args. Passed to ISR function.

• ISR

The Callback function. Must be in cap_isr_cb_t type, so it'll only recognized in the correct type with that format, need to have all these exact arguments, and return the bool value.

bool cap_ISR_cb(mcpwm_unit_t mcpwm, mcpwm_capture_channel_id_t cap_channel, const cap_event_data_t *edata,void *user_data);

The type definition inside library:

typedef bool (*cap_isr_cb_t)(mcpwm_unit_t mcpwm, mcpwm_capture_channel_id_t cap_channel, const cap_event_data_t *edata, void *user_data);

The bool return: Whether a task switch is needed after the callback function returns, this is usually due to the callback wakes up some high priority task.

• The arguments:

  • mcpwm_unit_t mcpwm: MCPWM unit(0-1).

  • mcpwm_capture_channel_id_t cap_channel: The capture channel ID.

  • const cap_event_data_t *edata: Capture event data, contains capture edge and capture value. cap_event_data_t definition:

     typedef struct {
    mcpwm_capture_on_edge_t cap_edge; /*!<Which signal edge is detected*/
    uint32_t cap_value;               /*!<Corresponding timestamp when event occurs. Clock rate = APB(usually 80M)*/
    } cap_event_data_t;

    Notice that is'nt the only way to get capture value. The function below also returns that value:

    uint32_t mcpwm_capture_signal_get_value(mcpwm_unit_t mcpwm_num, mcpwm_capture_signal_t cap_sig);

  • void *user_data: User registered data, passed from mcpwm_capture_config_t.

• GPIO Set

  Setting the gpio as Capture input. That function can init the gpio for any MCPWM Module (selected in mcpwm_io_signals_t io_signal).

esp_err_t mcpwm_gpio_init(mcpwm_unit_t mcpwm_num, mcpwm_io_signals_t io_signal, int gpio_num);

esp_err_t returns: Error flag, can be checked with ESP_ERROR_CHECK()

• The arguments:

  • mcpwm_unit_t mcpwm_num: MCPWM unit(0-1).
  • mcpwm_io_signals_t io_signal: Select wich MCPWM module io will be set. For capture:
    • MCPWM_CAP_0
    • MCPWM_CAP_1
    • MCPWM_CAP_2
  • int gpio_num: The gpio number.

• Capture Enable

  That function enable the capture with the settings in mcpwm_capture_config_t given.

esp_err_t mcpwm_capture_enable_channel(mcpwm_unit_t mcpwm_num, mcpwm_capture_channel_id_t cap_channel, const mcpwm_capture_config_t *cap_conf);

esp_err_t returns: Error flag, can be checked with ESP_ERROR_CHECK()

• The arguments:

  • mcpwm_unit_t mcpwm_num: MCPWM unit(0-1).
  • mcpwm_capture_channel_id_t cap_channel: Capture channel to enable.
    • MCPWM_SELECT_CAP0
    • MCPWM_SELECT_CAP1
    • MCPWM_SELECT_CAP2
  • const mcpwm_capture_config_t *cap_conf: Point to object type with all the capture configs.