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why does it take so long to retrieve the ADC conversion result?

Question asked by on Jul 10, 2018
Latest reply on Aug 14, 2018 by Felipe García

i'm using the ADC on the QN9080-DK, and found that i can't sample it faster than about 500 Hz, because these three lines:


while (!(ADC_GetStatusFlags(ADC) & kADC_DataReadyFlag)) {}
adcConvResult = ADC_GetConversionResult(ADC);


are taking 2 ms to complete (i tested this by toggling a GPIO pin before and after execution, and measuring the duration of the pulse with an oscilloscope). actually i find that the first 2 lines only take 12 microseconds, and it's the third line that takes 2 ms. why is the call to ADC_GetConversionResult() taking so long?


here's my ADC configuration:



adc_config_t adcConfigStruct;
adc_sd_config_t adcSdConfigStruct;

/* Initial ADC to default configuration */
adcConfigStruct.channelEnable = (1U << ADC_CHANNEL);
adcConfigStruct.channelConfig = (ADC_CFG_IDX << ADC_CHANNEL);
adcConfigStruct.triggerSource = kADC_TriggerSelectSoftware;
adcConfigStruct.convMode = kADC_ConvModeSingle;
adcConfigStruct.clock = kADC_Clock2M;
adcConfigStruct.dataFormat = kADC_ForceUnsigned;
ADC_Init(ADC, &adcConfigStruct);

/* Initial ADC Sigma Delta(SD) configuration */
ADC_SetSdConfig(ADC, ADC_CFG_IDX, &adcSdConfigStruct);

/* Enable ADC */
ADC_Enable(ADC, true);