void saadc_init(void)
{
NVIC_EnableIRQ(SAADC_IRQn);
NVIC_ClearPendingIRQ(SAADC_IRQn);
NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_10bit;
// Configure the SAADC channel with AIN0 (P0.02) as positive input, no negative input(single ended).
NRF_SAADC->CH[0].PSELP = SAADC_CH_PSELP_PSELP_AnalogInput0 << SAADC_CH_PSELP_PSELP_Pos;
NRF_SAADC->CH[0].PSELN = SAADC_CH_PSELN_PSELN_NC << SAADC_CH_PSELN_PSELN_Pos;
NRF_SAADC->CH[0].CONFIG = (( SAADC_CH_CONFIG_BURST_Disabled << SAADC_CH_CONFIG_BURST_Pos ) | // Burst mode is disabled (normal operation)
( SAADC_CH_CONFIG_MODE_SE << SAADC_CH_CONFIG_MODE_Pos ) | // Single ended, PSELN will be ignored, negative input to ADC shorted to GND
( SAADC_CH_CONFIG_TACQ_20us << SAADC_CH_CONFIG_TACQ_Pos ) | // Acquisition time, the time the ADC uses to sample the input voltage
( SAADC_CH_CONFIG_REFSEL_VDD1_4 << SAADC_CH_CONFIG_REFSEL_Pos ) | // VDD/4 as reference
( SAADC_CH_CONFIG_GAIN_Gain1_4 << SAADC_CH_CONFIG_GAIN_Pos ) | // Gain control
( SAADC_CH_CONFIG_RESN_Bypass << SAADC_CH_CONFIG_RESN_Pos ) | // Bypass resistor ladder
( SAADC_CH_CONFIG_RESP_Bypass << SAADC_CH_CONFIG_RESP_Pos )); // Bypass resistor ladder
// Configure sample rate. Minimum sample rate is 16,000,000/2047 = 7816.3 Samples pr second => 0.128ms interval
// Configure sample rate. Minimum sample rate is 16,000,000/8000 = 2000 Samples pr second
NRF_SAADC->SAMPLERATE = ( SAADC_SAMPLERATE_MODE_Timers << SAADC_SAMPLERATE_MODE_Pos) |
( 8000 << SAADC_SAMPLERATE_CC_Pos );
/* RAM Bufffer pointer for ADC Result*/
NRF_SAADC->RESULT.PTR =(uint32_t)&m_buffer_pool;
/* Number of Sample Count*/
NRF_SAADC->RESULT.MAXCNT = SAMPLES_IN_BUFFER;
// Enable SAADC END interrupt to do maintainance and printing of values.
NRF_SAADC->INTENSET = SAADC_INTENSET_END_Enabled << SAADC_INTENSET_END_Pos;
NVIC_EnableIRQ(SAADC_IRQn);
}
I have do a test accurate sampling interval used rtc0. I used ( 8000 << SAADC_SAMPLERATE_CC_Pos ), It must be 16,000,000/8000 = 2000 Samples pr second, INRF_SAADC->RESULT.MAXCNT = SAMPLES_IN_BUFFER is 100, add time count at SAADC_IRQHandler,
DEBUG output is
APP:DEBUG:
Time taken: 1.162201 sec
APP:DEBUG: Time taken: 2.322083 sec
APP:DEBUG: Time taken: 3.481964 sec
APP:DEBUG: Time taken: 4.641876 sec
APP:DEBUG: Time taken: 5.801758 sec
100*100 = 10000,must used 10000/samplerate(2000), is about 5sec.but in the log, it only used 1sec. why???
void SAADC_IRQHandler(void)
{
// Clear events
//NRF_LOG_INFO("SAADC_IRQHandler\r\n");
if(adc_count == 100)
{
adc_count = 0;
nrf_gpio_pin_clear(17);
counter=NRF_RTC0->COUNTER;
sprintf(tx_message, "\r\n Time taken: %6f sec \r\n", (float)counter/32768);
NRF_LOG_DEBUG("%s\r\n",(uint32_t)tx_message);
}
else
{
adc_count ++;
}
}
