MKL16 ADC read using DMA

[balkrishanaa]

Came across code for MKL16 controller, where ADC single channel data is read in DMA interrupt in "uint32 adc_data[4]". And after reading data using DMA_PrepareTransfer(), data in adc_data[1] is used while ignoring adc_data[0]. Code seems to work fine, what can be the justification for this? ADC is configured for differential conversion and auto calibration is enabled.

ADC configuration: resolution = 16 bit

longSampleMode = kADC16_LongSampleCycle24

enableContinuousConversion = false

enableInterruptOnConversionCompleted = false

enable dma = true 

sample code :

uint32AveragedReading;

uint32 adc_data[4];

//interrupt used for reading ADC data

DMA0_IRQHandler()

{

int data;

DMA_ClearChannelStatusFlags();

DMA_PrepareTransfer(&DMA_TransferConfig, (void *)(uint32_t)(&ADC0->R[0]), sizeof(uint32_t),
(void *)adc_data, sizeof(uint32_t), sizeof(adc_data),
kDMA_PeripheralToMemory);

data = adc_data[1];// why adc_data[0] is ignored?

AveragedReading = averaged_value_of_'data';

}

[balkrishanaa]

Hi Sabina,

Thanks for your help. I am trying to reach the developer who wrote this code and I will update this thread if he has any specific reasons for doing this.

Regards,

Balkrishana

[Sabina_Bruce]

Hi Balkrishna,

Could you please tell me which example you are working on and what version of the SDK it is?

Let me know as soon as you can, so I can assist you.

Thank you,

Sabina

[balkrishanaa]

Hi Simua,

Thanks for your reply. I am using "kds 2.2.0". And could you please tell what you mean by "which example you are working on"?

[Sabina_Bruce]

Hi Balkrishna,

You said that you "Came across code for MKL16 controller". In order for me to be able to better assist you I need to know where you located this code. 

If you can attach the project that would also be helpful.

Thank you,

Sabina

[balkrishanaa]

Hi Sabina,

Thanks for your reply. Actually, I am working on client project and I got this code from them. I am working on re-designing the code. I would not be able to share code. We are using this ADC to monitor photo-diode readings. Please let me know if you need any other configuration details.

Thanks,

Balkrishana 

[Sabina_Bruce]

Hi Balkrishana,

Thank you for the information you have provided. I tried replicating the code you provided, but the first sample is just as valid as the rest of the samples in the data[4] array. Unfortunately from our side there is no valid reason as to why ignore the first sample that is being read from the ADC. I believe this particular implementation will be specific to your client's needs. I would recommend that you ask them directly why this is being done.

Best Regards,

Sabina