Nordic nRF5 SDK 學習筆記之十三, SAADC

樣例: ~\nRF5_SDK_15.2.0_9412b96\examples\peripheral\saadc

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1. ADC 功能塊圖

2. ADC 計算公式

3. 於 sdk_config.h 中配置, 以及添加 nrfx_saadc.c 文件

4. nrf_drv_saadc_init 初始化

__STATIC_INLINE ret_code_t nrf_drv_saadc_init(nrf_drv_saadc_config_t const * p_config,
                                              nrf_drv_saadc_event_handler_t  event_handler)
{
    if (p_config == NULL)
    {
        static const nrfx_saadc_config_t default_config = NRFX_SAADC_DEFAULT_CONFIG;
        p_config = &default_config;
    }
    return nrfx_saadc_init(p_config, event_handler);
}

--------------------------------------------------------
#define NRFX_SAADC_DEFAULT_CONFIG                                               \
{                                                                               \
    .resolution         = (nrf_saadc_resolution_t)NRFX_SAADC_CONFIG_RESOLUTION, \
    .oversample         = (nrf_saadc_oversample_t)NRFX_SAADC_CONFIG_OVERSAMPLE, \
    .interrupt_priority = NRFX_SAADC_CONFIG_IRQ_PRIORITY,                       \
    .low_power_mode     = NRFX_SAADC_CONFIG_LP_MODE                             \
}

--------------------------------------------------------
typedef enum
{
    NRF_SAADC_RESOLUTION_8BIT  = SAADC_RESOLUTION_VAL_8bit,  ///< 8 bit resolution.
    NRF_SAADC_RESOLUTION_10BIT = SAADC_RESOLUTION_VAL_10bit, ///< 10 bit resolution.
    NRF_SAADC_RESOLUTION_12BIT = SAADC_RESOLUTION_VAL_12bit, ///< 12 bit resolution.
    NRF_SAADC_RESOLUTION_14BIT = SAADC_RESOLUTION_VAL_14bit  ///< 14 bit resolution.
} nrf_saadc_resolution_t;

?! 在使用 NRFX_SAADC_DEFAULT_CONFIG 配置時, 不管 sdk_config.h 中設備爲 8,10,12,14位時, ADC 解析率始終爲 10 bits!

5. ADC 通道配置

    nrf_saadc_channel_config_t channel_config = NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);
//		channel_config.gain = NRF_SAADC_GAIN1;		

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);
------------------------------------------------------------------
默認通道配置

#define NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(PIN_P) \
{                                                   \
    .resistor_p = NRF_SAADC_RESISTOR_DISABLED,      \
    .resistor_n = NRF_SAADC_RESISTOR_DISABLED,      \
    .gain       = NRF_SAADC_GAIN1_6,                \   增益: 1/6
    .reference  = NRF_SAADC_REFERENCE_INTERNAL,     \   內部參考電壓: 0.6V
    .acq_time   = NRF_SAADC_ACQTIME_10US,           \
    .mode       = NRF_SAADC_MODE_SINGLE_ENDED,      \   模式: 單端
    .burst      = NRF_SAADC_BURST_DISABLED,         \
    .pin_p      = (nrf_saadc_input_t)(PIN_P),       \
    .pin_n      = NRF_SAADC_INPUT_DISABLED          \
}

6. 單次 ADC 轉換 nrf_drv_saadc_sample_convert()

#define nrf_drv_saadc_sample_convert    nrfx_saadc_sample_convert

函數原型
nrfx_err_t nrfx_saadc_sample_convert(uint8_t channel, nrf_saadc_value_t * p_value)
{
    nrfx_err_t err_code;

    if (m_cb.adc_state != NRF_SAADC_STATE_IDLE)
    {
        err_code = NRFX_ERROR_BUSY;
        NRFX_LOG_WARNING("Function: %s error code: %s.",
                         __func__,
                         NRFX_LOG_ERROR_STRING_GET(err_code));
        return err_code;
    }
    m_cb.adc_state = NRF_SAADC_STATE_BUSY;
    nrf_saadc_int_disable(NRF_SAADC_INT_STARTED | NRF_SAADC_INT_END);
    nrf_saadc_buffer_init(p_value, 1);
    if (m_cb.active_channels > 1)
    {
        for (uint32_t i = 0; i < NRF_SAADC_CHANNEL_COUNT; ++i)
        {
            nrf_saadc_channel_input_set(i, NRF_SAADC_INPUT_DISABLED, NRF_SAADC_INPUT_DISABLED);
        }
    }
    nrf_saadc_channel_input_set(channel, m_cb.psel[channel].pselp, m_cb.psel[channel].pseln);
    nrf_saadc_task_trigger(NRF_SAADC_TASK_START);
    nrf_saadc_task_trigger(NRF_SAADC_TASK_SAMPLE);

    bool result;
    NRFX_WAIT_FOR(nrf_saadc_event_check(NRF_SAADC_EVENT_END), HW_TIMEOUT, 0, result);
    NRFX_ASSERT(result);

    nrf_saadc_event_clear(NRF_SAADC_EVENT_STARTED);
    nrf_saadc_event_clear(NRF_SAADC_EVENT_END);

    NRFX_LOG_INFO("Conversion value: %d, channel %d.", *p_value, channel);

    if (m_cb.active_channels > 1)
    {
        for (uint32_t i = 0; i < NRF_SAADC_CHANNEL_COUNT; ++i)
        {
            nrf_saadc_channel_input_set(i, m_cb.psel[i].pselp, m_cb.psel[i].pseln);
        }
    }

    if (m_cb.low_power_mode)
    {
        nrf_saadc_int_enable(NRF_SAADC_INT_STARTED | NRF_SAADC_INT_END);
    }
    else
    {
        nrf_saadc_int_enable(NRF_SAADC_INT_END);
    }

    m_cb.adc_state = NRF_SAADC_STATE_IDLE;

    err_code = NRFX_SUCCESS;
    NRFX_LOG_WARNING("Function: %s, error code: %s.",
                     __func__,
                     NRFX_LOG_ERROR_STRING_GET(err_code));
    return err_code;
}

7. 配置 EasyDMA

#define nrf_drv_saadc_buffer_convert    nrfx_saadc_buffer_convert

nrfx_err_t nrfx_saadc_buffer_convert(nrf_saadc_value_t * p_buffer, uint16_t size)

-----------------------------------------------------------------
example:

#define SAMPLES_IN_BUFFER 5
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];

nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);

8. SAADC 正式採集函數

#define nrf_drv_saadc_sample            nrfx_saadc_sample