nRF52 SAADC 直接操作寄存器

#include<nrf.h>

int main(void)
{
　　volatile int16_t result = 0;
　　volatile float precise_result = 0;

　　// Start HFCLK from crystal oscillator, this will give the SAADC higher accuracy
　　NRF_CLOCK->TASKS_HFCLKSTART = 1;
　　while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
　　NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

　　// Configure SAADC singled-ended channel, Internal reference (0.6V) and 1/6 gain.
　  NRF_SAADC->CH[0].CONFIG = (SAADC_CH_CONFIG_GAIN_Gain1_6 << SAADC_CH_CONFIG_GAIN_Pos) |
　　(SAADC_CH_CONFIG_MODE_SE << SAADC_CH_CONFIG_MODE_Pos) |
　　(SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos) |
　　(SAADC_CH_CONFIG_RESN_Bypass << SAADC_CH_CONFIG_RESN_Pos) |
　　(SAADC_CH_CONFIG_RESP_Bypass << SAADC_CH_CONFIG_RESP_Pos) |
　　(SAADC_CH_CONFIG_TACQ_3us << SAADC_CH_CONFIG_TACQ_Pos);

　　// Configure the SAADC channel with VDD as positive input, no negative input(single ended).
　　NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_VDD << SAADC_CH_PSELP_PSELP_Pos;
　　NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;

　　// Configure the SAADC resolution.
　　NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_14bit << SAADC_RESOLUTION_VAL_Pos;

　　// Configure result to be put in RAM at the location of "result" variable.
　　NRF_SAADC->RESULT.MAXCNT = 1;
　　NRF_SAADC->RESULT.PTR = (uint32_t)&result;

　　// No automatic sampling, will trigger with TASKS_SAMPLE.
　　NRF_SAADC->SAMPLERATE = SAADC_SAMPLERATE_MODE_Task << SAADC_SAMPLERATE_MODE_Pos;

　　// Enable SAADC (would capture analog pins if they were used in CH[0].PSELP)
　　NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;

　　// Calibrate the SAADC (only needs to be done once in a while)
　　NRF_SAADC->TASKS_CALIBRATEOFFSET = 1;
　　while (NRF_SAADC->EVENTS_CALIBRATEDONE == 0);
　　NRF_SAADC->EVENTS_CALIBRATEDONE = 0;
　　while (NRF_SAADC->STATUS == (SAADC_STATUS_STATUS_Busy <<SAADC_STATUS_STATUS_Pos));

　　// Start the SAADC and wait for the started event.
　　NRF_SAADC->TASKS_START = 1;
　　while (NRF_SAADC->EVENTS_STARTED == 0);
　　NRF_SAADC->EVENTS_STARTED = 0;

　　// Do a SAADC sample, will put the result in the configured RAM buffer.
　　NRF_SAADC->TASKS_SAMPLE = 1;
　　while (NRF_SAADC->EVENTS_END == 0);
　　NRF_SAADC->EVENTS_END = 0;

　　// Convert the result to voltage
　　// Result = [V(p) - V(n)] * GAIN/REFERENCE * 2^(RESOLUTION)
　　// Result = (VDD - 0) * ((1/6) / 0.6) * 2^14
　　// VDD = Result / 4551.1
　　precise_result = (float)result / 4551.1f;
　　precise_result; // to get rid of set but not used warning

　　// Stop the SAADC, since it's not used anymore.
　　NRF_SAADC->TASKS_STOP = 1;
　　while (NRF_SAADC->EVENTS_STOPPED == 0);
　　NRF_SAADC->EVENTS_STOPPED = 0;

　　while (1)
　　{
　　　　__WFE();
　　}
}