NRF51822自学笔记（二）PWM
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PWM这个东西我在32上用来电机调速过……通过改变高低电平占空比来实现一些功能。
keil的nrf51822目录下没有pwm.c..就在网上找了个pwm蜂鸣器的例程……看画风应该是官方的……吧……
例程的define为NRF51 SETUPA BOARD_PCA10028..修改一下，设置如下。
然后通过两个灯来实现一下两路pwm波……pin为20和21的LED_2和LED_3
先看main.c（非例程）
#include <stdbool.h>#include <stdint.h>#include "nrf_delay.h"#include "nrf_gpio.h"#include "boards.h"#include "nrf_pwm.h"/** * @brief Function for application main entry. */int main(void){ // Configure LED-pins as outputs nrf_gpio_cfg_output(20); nrf_gpio_cfg_output(21); nrf_pwm_config_t pwm_config = PWM_DEFAULT_CONFIG; pwm_config.mode = PWM_MODE_LED_255; pwm_config.num_channels = 2; pwm_config.gpio_num[0] = 21; pwm_config.gpio_num[1] = 20; nrf_pwm_init(&pwm_config); nrf_pwm_set_value(0,20); nrf_pwm_set_value(1,255);}第一步把要操作的灯的pin配置一下，设置成outputs
第二步用一个结构体来设置一下PWM的一些参数。
追踪一下PWM_DEFAULT_CONFIG，发现它在PWM.H里
#define PWM_DEFAULT_CONFIG {.num_channels = 2, \ .gpio_num = {8,9,10,11}, \ .ppi_channel = {0,1,2,3,4,5,6,7}, \ .gpiote_channel = {2,3,0,1}, \ .mode = PWM_MODE_LED_100};然后配置mode为PWM_MODE_LED_255，两个通道，两个通道的pin为21和20。把结构体地址传给初始化函数，初始化之后调用nrf_pwm_set_value()来设置一下占空比。追踪一下那个mode
typedef enum{ PWM_MODE_LED_100, // 0-100 resolution, 156Hz PWM frequency, 32kHz timer frequency (prescaler 9) PWM_MODE_LED_255, // 8-bit resolution, 122Hz PWM frequency, 32kHz timer frequency (prescaler 9) PWM_MODE_LED_1000, // 0-1000 resolution, 125Hz PWM frequency, 250kHz timer frequency (prescaler 6) PWM_MODE_MTR_100, // 0-100 resolution, 20kHz PWM frequency, 2MHz timer frequency (prescaler 3) PWM_MODE_MTR_255, // 8-bit resolution, 31kHz PWM frequency, 8MHz timer frequency (prescaler 1) PWM_MODE_BUZZER_255 // 8-bit resolution, 62.5kHz PWM frequency, 16MHz timer frequency (prescaler 0)} nrf_pwm_mode_t;= =一堆枚举常量，LED，蜂鸣器和MTR。在初始化函数里利用它们和switch语句实现了配置……uint32_t nrf_pwm_init(nrf_pwm_config_t *config){ if(config->num_channels == 0 || config->num_channels > PWM_MAX_CHANNELS) return 0xFFFFFFFF; switch(config->mode) { case PWM_MODE_LED_100: // 0-100 resolution, 321Hz PWM frequency, 32kHz timer frequency (prescaler 9) PWM_TIMER->PRESCALER = 9; pwm_max_value = 100; break; case PWM_MODE_LED_255: // 8-bit resolution, 122Hz PWM frequency, 32kHz timer frequency (prescaler 9) PWM_TIMER->PRESCALER = 9; pwm_max_value = 255; break; case PWM_MODE_LED_1000: // 0-1000 resolution, 250Hz PWM frequency, 250kHz timer frequency (prescaler 6) PWM_TIMER->PRESCALER = 6; pwm_max_value = 1000; break; case PWM_MODE_MTR_100: // 0-100 resolution, 20kHz PWM frequency, 2MHz timer frequency (prescaler 3) PWM_TIMER->PRESCALER = 3; pwm_max_value = 100; break; case PWM_MODE_MTR_255: // 8-bit resolution, 31kHz PWM frequency, 8MHz timer frequency (prescaler 1) PWM_TIMER->PRESCALER = 1; pwm_max_value = 255; break; case PWM_MODE_BUZZER_255: // 8-bit resolution, 62.5kHz PWM frequency, 16MHz timer frequency (prescaler 0) PWM_TIMER->PRESCALER = 0; pwm_max_value = 255; break; default: return 0xFFFFFFFF; } pwm_cc_update_margin_ticks = pwm_cc_margin_by_prescaler[PWM_TIMER->PRESCALER]; pwm_num_channels = config->num_channels; for(int i = 0; i < pwm_num_channels; i++) { pwm_io_ch[i] = (uint32_t)config->gpio_num[i]; nrf_gpio_cfg_output(pwm_io_ch[i]); pwm_running[i] = 0; pwm_gpiote_channel[i] = config->gpiote_channel[i]; } PWM_TIMER->TASKS_CLEAR = 1; PWM_TIMER->BITMODE = TIMER_BITMODE_BITMODE_16Bit; PWM_TIMER->CC[2] = pwm_next_max_value = pwm_max_value;PWM_TIMER->MODE = TIMER_MODE_MODE_Timer; PWM_TIMER->SHORTS = TIMER_SHORTS_COMPARE2_CLEAR_Msk; PWM_TIMER->EVENTS_COMPARE[0] = PWM_TIMER->EVENTS_COMPARE[1] = PWM_TIMER->EVENTS_COMPARE[2] = PWM_TIMER->EVENTS_COMPARE[3] = 0; if(pwm_num_channels > 2) { PWM_TIMER2->TASKS_CLEAR = 1; PWM_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_16Bit; PWM_TIMER2->CC[2] = pwm_next_max_value = pwm_max_value; PWM_TIMER2->MODE = TIMER_MODE_MODE_Timer; PWM_TIMER2->SHORTS = TIMER_SHORTS_COMPARE2_CLEAR_Msk; PWM_TIMER2->EVENTS_COMPARE[0] = PWM_TIMER2->EVENTS_COMPARE[1] = PWM_TIMER2->EVENTS_COMPARE[2] = PWM_TIMER2->EVENTS_COMPARE[3] = 0; PWM_TIMER2->PRESCALER = PWM_TIMER->PRESCALER; } for(int i = 0; i < pwm_num_channels && i < 2; i++) { ppi_enable_channel(config->ppi_channel[i*2], &PWM_TIMER->EVENTS_COMPARE[i], &NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]]); ppi_enable_channel(config->ppi_channel[i*2+1],&PWM_TIMER->EVENTS_COMPARE[2], &NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]]); pwm_modified[i] = false; } for(int i = 2; i < pwm_num_channels; i++) { ppi_enable_channel(config->ppi_channel[i*2], &PWM_TIMER2->EVENTS_COMPARE[i-2], &NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]]); ppi_enable_channel(config->ppi_channel[i*2+1],&PWM_TIMER2->EVENTS_COMPARE[2], &NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]]); pwm_modified[i] = false; }#if(USE_WITH_SOFTDEVICE == 1) sd_radio_session_open(nrf_radio_signal_callback);#else NVIC_SetPriority(PWM_IRQn, 0); NVIC_EnableIRQ(PWM_IRQn);#endif apply_pan73_workaround(PWM_TIMER, true); PWM_TIMER->TASKS_START = 1; if(pwm_num_channels > 2) { apply_pan73_workaround(PWM_TIMER2, true); PWM_TIMER2->TASKS_START = 1; } return 0;}当通道数大于2时，就要使用TIMER2了。下面是设置占空比的void nrf_pwm_set_value(uint32_t pwm_channel, uint32_t pwm_value){ pwm_next_value[pwm_channel] = pwm_value; pwm_modified[pwm_channel] = true;#if(USE_WITH_SOFTDEVICE == 1) nrf_radio_request_t radio_request; radio_request.request_type = NRF_RADIO_REQ_TYPE_EARLIEST; radio_request.params.earliest.hfclk = NRF_RADIO_HFCLK_CFG_DEFAULT; radio_request.params.earliest.length_us = 250; radio_request.params.earliest.priority = NRF_RADIO_PRIORITY_HIGH; radio_request.params.earliest.timeout_us = 100000; sd_radio_request(&radio_request);#else NVIC_SetPendingIRQ(PWM_IRQn);#endifvoid nrf_pwm_set_values(uint32_t pwm_channel_num, uint32_t *pwm_values){ for(int i = 0; i < pwm_channel_num; i++) { pwm_next_value[i] = pwm_values[i]; pwm_modified[i] = true; }#if(USE_WITH_SOFTDEVICE == 1) nrf_radio_request_t radio_request; radio_request.request_type = NRF_RADIO_REQ_TYPE_EARLIEST; radio_request.params.earliest.hfclk = NRF_RADIO_HFCLK_CFG_DEFAULT; radio_request.params.earliest.length_us = 250; radio_request.params.earliest.priority = NRF_RADIO_PRIORITY_HIGH; radio_request.params.earliest.timeout_us = 100000; sd_radio_request(&radio_request);#else NVIC_SetPendingIRQ(PWM_IRQn);#endif}这两个函数功能是一样的……区别在后者先设置好了一组数……最后看看中断服务函数
void PWM_IRQHandler(void){ static uint32_t i, new_capture, old_capture; PWM_TIMER->CC[2] = pwm_max_value = pwm_next_max_value; if(pwm_num_channels > 2) PWM_TIMER2->CC[2] = pwm_max_value; for(i = 0; i < pwm_num_channels; i++) { if(pwm_modified[i]) { pwm_modified[i] = false; if(pwm_next_value[i] == 0) { nrf_gpiote_unconfig(pwm_gpiote_channel[i]); nrf_gpio_pin_write(pwm_io_ch[i], 0); pwm_running[i] = 0; } else if (pwm_next_value[i] >= pwm_max_value) { nrf_gpiote_unconfig(pwm_gpiote_channel[i]); nrf_gpio_pin_write(pwm_io_ch[i], 1); pwm_running[i] = 0; } else { if(i < 2) { new_capture = pwm_next_value[i]; old_capture = PWM_TIMER->CC[i]; if(!pwm_running[i]) { nrf_gpiote_task_config(pwm_gpiote_channel[i], pwm_io_ch[i], NRF_GPIOTE_POLARITY_TOGGLE, NRF_GPIOTE_INITIAL_VALUE_HIGH); pwm_running[i] = 1; PWM_TIMER->TASKS_CAPTURE[3] = 1; if(PWM_TIMER->CC[3] > new_capture) NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]] = 1; PWM_TIMER->CC[i] = new_capture; } else { while(1) { PWM_TIMER->TASKS_CAPTURE[3] = 1; if(safe_margins_present(PWM_TIMER_CURRENT, old_capture) && safe_margins_present(PWM_TIMER_CURRENT, new_capture)) break; } if((PWM_TIMER_CURRENT >= old_capture && PWM_TIMER_CURRENT < new_capture) || (PWM_TIMER_CURRENT < old_capture && PWM_TIMER_CURRENT >= new_capture)) { NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]] = 1; } PWM_TIMER->CC[i] = new_capture; } } else { new_capture = pwm_next_value[i]; old_capture = PWM_TIMER2->CC[i-2]; if(!pwm_running[i]) { nrf_gpiote_task_config(pwm_gpiote_channel[i], pwm_io_ch[i], NRF_GPIOTE_POLARITY_TOGGLE, NRF_GPIOTE_INITIAL_VALUE_HIGH); pwm_running[i] = 1; PWM_TIMER2->TASKS_CAPTURE[3] = 1; if(PWM_TIMER2->CC[3] > new_capture) NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]] = 1; PWM_TIMER2->CC[i-2] = new_capture; } else { while(1) { PWM_TIMER2->TASKS_CAPTURE[3] = 1; if(safe_margins_present(PWM_TIMER2_CURRENT, old_capture) && safe_margins_present(PWM_TIMER2_CURRENT, new_capture)) break; } if((PWM_TIMER2_CURRENT >= old_capture && PWM_TIMER2_CURRENT < new_capture) || (PWM_TIMER2_CURRENT < old_capture && PWM_TIMER2_CURRENT >= new_capture)) { NRF_GPIOTE->TASKS_OUT[pwm_gpiote_channel[i]] = 1; } PWM_TIMER2->CC[i-2] = new_capture; } } } } }然后运行一下~会看见占空比不同，两个led灯的亮度不同。占空比为255的LED_1要比占空比为20的LED_1亮 0 1
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