Compiler/CC2640R2F: ADC sampling issue

Tool/software: TI C/C++ Compiler

Hi,

I am working on an ultra low power application on CC2640R2 and I have an issue with the ADC. 

Requirements are:

• Sampling of three channels in sequence.
• One sample from each channel as fast as possible.
• Non-blocking.
• Sampling interval: 1 second.

My configuration is as follows:

static ADCBuf_Handle handle;

static ADCBuf_Params params;

static ADCBufCC26XX_ParamsExtension customParams;

static ADCBuf_Conversion conv1;

static ADCBuf_Conversion conv2;

static ADCBuf_Conversion conv3;

static uint16_t conv1Buf;

static uint16_t conv2Buf;

static uint16_t conv3Buf;

ADCBuf_init();

ADCBuf_Params_init(&params);

params.returnMode = ADCBuf_RETURN_MODE_CALLBACK;

params.blockingTimeout = 25000;

params.callbackFxn = GF_Adc_AdcBufCb;

params.recurrenceMode = ADCBuf_RECURRENCE_MODE_ONE_SHOT;

params.samplingFrequency = XXXXX;

customParams.samplingDuration = ADCBufCC26XX_SAMPLING_DURATION_5P3_US;

customParams.refSource = ADCBufCC26XX_FIXED_REFERENCE;

customParams.samplingMode = ADCBufCC26XX_SAMPING_MODE_SYNCHRONOUS;

customParams.inputScalingEnabled = true;

params.custom = &customParams;

conv1.samplesRequestedCount = NO_OF_NTC_SAMPLES;  // 1

conv1.sampleBuffer = &conv1Buf;

conv1.sampleBufferTwo = NULL;

conv1.arg = NULL;

conv1.adcChannel = Board_ADCBUF0CHANNEL5;

conv2.samplesRequestedCount = NO_OF_NTC_SAMPLES;  // 1

conv2.sampleBuffer = &conv2Buf;

conv2.sampleBufferTwo = NULL;

conv2.arg = NULL;

conv2.adcChannel = Board_ADCBUF0CHANNEL6;

conv3.samplesRequestedCount = NO_OF_NTC_SAMPLES;  // 1

conv3.sampleBuffer = &conv3Buf;

conv3.sampleBufferTwo = NULL;

conv3.arg = NULL;

conv3.adcChannel = Board_ADCBUF0CHANNEL7;

The sampling sequence is as follows:

1. Open ADC (in main thread): ADCBuf_Handle handle = ADCBuf_open(Board_ADCBUF0, &params)
2. If handle != NULL (in main thread): ADCBuf_convert(ADCBuf_Handle handle, ADCBuf_Conversion conv1, SINGLE_CHANNEL)
3. In ADC callback: ADCBuf_convert(ADCBuf_Handle handle, ADCBuf_Conversion conv2, SINGLE_CHANNEL)
4. In ADC callback: ADCBuf_convert(ADCBuf_Handle handle, ADCBuf_Conversion conv3, SINGLE_CHANNEL)
5. In ADC callback: Enqueue ADC finished event.
6. Handle ADC finished event - Close ADC (in main thread): ADCBuf_close(handle)

The issue is that the call to ADCBuf_convert() does not always return. It can be fixed by drastically reducing the 'params.samplingFrequency' parameter. This is not acceptable as the CC2640R2 is not in sleep mode for a very long time (several ms) during sampling of the three ADC channels.

How can I fix this issue?

Looking forward to hear from you.

-Annette