ADC Resolution

[s7v7n92]

Posted on August 08, 2014 at 17:29

ADC resolution 12 bits(with 16 bit buffer) works but 8 bit(with 8bit buffer) results in the code going into an infinite loop in the DMA ISR. 

__IO uint8_t buffer[1000];/* ADC Config*/  ADC_StructInit(&ADC_InitStructure);  ADC_InitStructure.ADC_Resolution = ADC_Resolution_8b;  ADC_InitStructure.ADC_ScanConvMode = DISABLE;  ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;  ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_Rising;  ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T3_TRGO;  ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;  ADC_InitStructure.ADC_NbrOfConversion = 1;  ADC_Init(ADC1, &ADC_InitStructure);  ADC_RegularChannelConfig(ADC1, ADC_Channel_1, 1, ADC_SampleTime_192Cycles); #adc #stm32l151

[Tesla DeLorean]

Posted on August 08, 2014 at 17:46

ADC resolution 12 bits(with 16 bit buffer) works but 8 bit(with 8bit buffer) results in the code going into an infinite loop in the DMA ISR.

Code that you conveniently fail to provide...

[s7v7n92]

Posted on August 08, 2014 at 17:55

I have included the code that is relevant to the problem. I don't think its a problem in the DMA_ISR. Its something in the way the ADC/Buffer works or sampling rate. ADC Is being sampled at 10KHz

void DMA1_Channel1_IRQHandler(void){  if(flag)  {    /*do something/*  }   else  {    /*do something else*/  }    /*Clear DMA Channel Transfer Complete interrupt pending bit */  DMA_ClearITPendingBit(DMA1_IT_TC1);}

[raptorhal2]

Posted on August 08, 2014 at 19:07

Check the Data Alignment section in the reference manual. Byte alignment happens only for 6 bit conversions.

Hal

[s7v7n92]

Posted on August 08, 2014 at 20:08

Hello Hal!

Thanks for your response. Yes, I checked the ref manual and as you said only 6b and 12b can be aligned. But by default ADC_StructInit(&ADC_InitStructure); aligns by right. Also the problem does not happen when I use a 16 bit buffer. I am trying to store microphone data so would I need to do some processing to make it in PCM format or is the ADC data captured read for playback?Thanks!kj

[Tesla DeLorean]

Posted on August 08, 2014 at 20:27

I have included the code that is relevant to the problem.

If you knew what code was problematic you wouldn't be here asking. Present a sufficiently complete example that can be evaluated. Most likely you aren't configuring the DMA properly, but how can I judge that? Where you clear the interrupt you'll currently tickle a Cortex-M3 hazard, you really should qualify the IT flag and clear it early.