Nrf52832 SAADC

本文主要是介绍Nrf52832 SAADC，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

一. 测试平台

       环境：win10,64位，MDK集成开发环境.
       SDK：nRF5_SDK_15.2
       协议栈：s132_nrf52_6.1_softdevice.hex.
       硬件平台：pca10040开发板

参考例程：nRF5_SDK_15.2.0_9412b96\examples\peripheral\saadc

ADC的最快采样时间为5us采样一个点，如果为两通道扫描采样的话，最快为10us采样一次

二. Application移植

1. 添加相关头文件

#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"

2. SAADC的工作模式

（1）. 单次采样模式

SAADC初始化

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
//   
}void saadc_init(void)
{ret_code_t err_code;nrf_saadc_channel_config_t channel_config =NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);err_code = nrf_drv_saadc_init(NULL, saadc_callback);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_channel_init(0, &channel_config);APP_ERROR_CHECK(err_code);}

启动一次ADC采样，获取ADC值

nrf_drv_saadc_sample_convert(0,&saadc_val);

（2）.单缓冲中断模式

SAADC初始化，相关中断函数

#define SAMPLES_IN_BUFFER 6
static nrf_saadc_value_t       m_buffer_pool[SAMPLES_IN_BUFFER];void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{   float  val; if (p_event->type == NRF_DRV_SAADC_EVT_DONE){ret_code_t err_code;//设置好缓存，为下次转换预备缓冲err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);APP_ERROR_CHECK(err_code);int i;for (i = 0; i < p_event->data.done.size; i++){val = p_event->data.done.p_buffer[i] * 3.6 /1024;	printf("Voltage = %.3fV\r\n", val);}}
}void saadc_init(void)
{ret_code_t err_code;nrf_saadc_channel_config_t channel_0_config =NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN2);err_code = nrf_drv_saadc_init(NULL, saadc_callback);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_channel_init(0, &channel_0_config);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool,SAMPLES_IN_BUFFER);APP_ERROR_CHECK(err_code);
}

启动一次ADC采样，要采样次数等于SAMPLES_IN_BUFFER时，才会进入中断

nrf_drv_saadc_sample();

（3）.双缓冲PPI采样

用PPI的方式去触发SAADC，工作方式如下所示：

所以相对之前的初始化会复杂一点，需要初始化定时器，设置采样时间（这个采样时间是采样一个点的时间，如果采样时间设置为400ms，采集5个点，则全部的采样时间为400*5=2s。如果为两个通道，则400ms取两个点，取五次），设置PPI通道，初始化SAADC

#define SAMPLES_IN_BUFFER 5static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;void timer_handler(nrf_timer_event_t event_type, void * p_context)
{}void saadc_sampling_event_init(void)
{ret_code_t err_code;err_code = nrf_drv_ppi_init();APP_ERROR_CHECK(err_code);nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);APP_ERROR_CHECK(err_code);/* setup m_timer for compare event every 400ms */uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 400);nrf_drv_timer_extended_compare(&m_timer,NRF_TIMER_CC_CHANNEL0,ticks,NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,false);nrf_drv_timer_enable(&m_timer);uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,NRF_TIMER_CC_CHANNEL0);uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();/* setup ppi channel so that timer compare event is triggering sample task in SAADC */err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);APP_ERROR_CHECK(err_code);err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,timer_compare_event_addr,saadc_sample_task_addr);APP_ERROR_CHECK(err_code);
}void saadc_sampling_event_enable(void)
{ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);APP_ERROR_CHECK(err_code);
}void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{if (p_event->type == NRF_DRV_SAADC_EVT_DONE){ret_code_t err_code;err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);APP_ERROR_CHECK(err_code);int i;for (i = 0; i < SAMPLES_IN_BUFFER; i++){NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);}}
}void saadc_init(void)
{ret_code_t err_code;nrf_saadc_channel_config_t channel_config =NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);err_code = nrf_drv_saadc_init(NULL, saadc_callback);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_channel_init(0, &channel_config);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);APP_ERROR_CHECK(err_code);err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);APP_ERROR_CHECK(err_code);}

启动ADC,值需要初始化ADC即可，数据会不停的缓冲在easydma中，每次数据需要及时读取，不然会被覆盖掉。

saadc_init();
saadc_sampling_event_init();
saadc_sampling_event_enable();

防止数据覆盖的方式：

①采样完之后，在ADC中断函数中关掉定时器，等数据处理完再开启定时器，可以用下面两条语句

nrf_drv_timer_disable(&m_timer);
nrf_drv_timer_enable(&m_timer);

② 同时将ADC,PPI,TIMER都关掉，可以有效降低功耗

启动ADC

void ADC_PWM_START(void)
{nrf_saadc_enable();nrf_saadc_task_trigger(NRF_SAADC_TASK_START);nrf_drv_timer_enable(&m_timer);
}

关闭ADC,需要将相关标志位清楚，不然会导致错误

void ADC_PWM_STOP(void)
{nrf_drv_timer_disable(&m_timer);nrf_saadc_task_trigger(NRF_SAADC_TASK_STOP);nrf_saadc_event_clear(NRF_SAADC_EVENT_STARTED);nrf_saadc_event_clear(NRF_SAADC_EVENT_END);nrf_saadc_disable();
}

（4）采样数据的存放方式

在模式2和3中，如果是多通道的话，数据将会交替存放，如下所示：

假设采集数据为3，通道为2