nRF52 PWM 使用

SDK15.2

1. nRF52 PWM 模块

2. 使能PWM模块

在sdk_config.h文件使能PWM Module

#define NRFX_PWM_ENABLED 1
#define PWM_ENABLED 1
#define PWM0_ENABLED 1
#define NRFX_PWM0_ENABLED 0

总共支持4个PWM，分别是 PWM0, PWM1, PWM2, PWM3.

3. 实例化PWM

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

4. 初始化PWM

nrf_drv_pwm_config_t const config0 ={.output_pins ={3 | NRF_DRV_PWM_PIN_INVERTED,         // channel 0NRF_DRV_PWM_PIN_NOT_USED,             // channel 1NRF_DRV_PWM_PIN_NOT_USED,             // channel 2NRF_DRV_PWM_PIN_NOT_USED,             // channel 3},.irq_priority = APP_IRQ_PRIORITY_LOWEST,.base_clock = NRF_PWM_CLK_500kHz,.count_mode = NRF_PWM_MODE_UP,.top_value = 800,.load_mode = NRF_PWM_LOAD_COMMON,.step_mode = NRF_PWM_STEP_AUTO};APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, pwm_handler));

配置信息包好输出引脚，中断优先级，基础频率，计数模式，计数最大阈值，加载序列模式和step模式。

4.1 输出引脚设置

使用NRF_DRV_PWM_PIN_INVERTED可以设置空闲引脚的电平为高电平。不使用时空闲引脚的电平为低电平。
不使用引脚，需要设置为NRF_DRV_PWM_PIN_NOT_USED。

4.2 加载模式设置

PWM模块可以播放存在RAM中的Multiple duty cycle array(sequences)。也就是存一系列占空比值compare到RAM中，通过Decoder可以把这些值自动写入到寄存器。

NRF_PWM_LOAD_COMMON 4通道共用一个配置，通常使用这种模式即可。
NRF_PWM_LOAD_GROUPED 1,2通道使用第一个值；3,4通道使用第二个值。依次类推。
NRF_PWM_LOAD_INDIVIDUAL 完全独立，1通道对应第一个值，4通道对应第四个值。
NRF_PWM_LOAD_WAVE_FORM 1,2,3独立，第四个值写入 top value

4.3 基础频率和顶值设置

基础频率和顶值设置可以决定PWM的频率。

4.4 回调函数

typedef enum
{NRFX_PWM_EVT_FINISHED, ///< Sequence playback finished.NRFX_PWM_EVT_END_SEQ0, /**< End of sequence 0 reached. Its data can besafely modified now. */NRFX_PWM_EVT_END_SEQ1, /**< End of sequence 1 reached. Its data can besafely modified now. */NRFX_PWM_EVT_STOPPED,  ///< The PWM peripheral has been stopped.
} nrfx_pwm_evt_type_t;void brnc_drv_motor_pwm_handler(nrf_drv_pwm_evt_type_t event_type) {if (event_type == NRF_DRV_PWM_EVT_FINISHED) {}
}

5. 播放

5.1 播放参数设置

static nrf_pwm_values_common_t seq_values[] =
{0, 200, 400, 600, 800
};
nrf_pwm_sequence_t const seq =
{.values.p_common = seq_values,.length          = NRF_PWM_VALUES_LENGTH(seq_values),.repeats         = 0,.end_delay       = 0
};

5.2 播放

nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 3, NRF_DRV_PWM_FLAG_LOOP);
nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 3, NRFX_PWM_FLAG_STOP);

/*** @brief Function for starting a single sequence playback.** To take advantage of the looping mechanism in the PWM peripheral, both* sequences must be used (single sequence can be played back only once by* the peripheral). Therefore, the provided sequence is internally set and* played back as both sequence 0 and sequence 1. Consequently, if end of* sequence notifications are required, events for both sequences should be* used (that means that both the @ref NRFX_PWM_FLAG_SIGNAL_END_SEQ0 flag* and the @ref NRFX_PWM_FLAG_SIGNAL_END_SEQ1 flag should be specified and* the @ref NRFX_PWM_EVT_END_SEQ0 event and the @ref NRFX_PWM_EVT_END_SEQ1* event should be handled in the same way).** Use the @ref NRFX_PWM_FLAG_START_VIA_TASK flag if you want the playback* to be only prepared by this function, and you want to start it later by* triggering a task (using PPI for instance). The function will then return* the address of the task to be triggered.** @note The array containing the duty cycle values for the specified sequence*       must be in RAM and cannot be allocated on stack.*       For detailed information, see @ref nrf_pwm_sequence_t.** @param[in] p_instance     Pointer to the driver instance structure.* @param[in] p_sequence     Sequence to be played back.* @param[in] playback_count Number of playbacks to be performed (must not be 0).* @param[in] flags          Additional options. Pass any combination of*                           @ref nrfx_pwm_flag_t "playback flags", or 0*                           for default settings.** @return Address of the task to be triggered to start the playback if the @ref*         NRFX_PWM_FLAG_START_VIA_TASK flag was used, 0 otherwise.*/
uint32_t nrfx_pwm_simple_playback(nrfx_pwm_t const * const   p_instance,nrf_pwm_sequence_t const * p_sequence,uint16_t                   playback_count,uint32_t                   flags);

6. 停止与卸载

6.1 停止

bool nrfx_pwm_stop(nrfx_pwm_t const * const p_instance,bool wait_until_stopped);

6.2 卸载

void nrfx_pwm_uninit(nrfx_pwm_t const * const p_instance);

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