The signal Produced by DAC has errors

[HBesi.1]

Hello,

I am building and electric field sensor. The driver signal for it is produced via DAC of the STM32F767zi microcontroller. The signal is 4 kHz and is generated at a sampling speed of 80 kHz via DMA and TIM6. As you can see from the picture the signal has errors in it like every 10-20 wavelengths there is 1 corrupted sample.

Best regards

[Vangelis Fortounas]

Hello

seems like interruption from a higher priority interrupt routines causes DMA underruns.

[waclawek.jan]

But would underrun result in an unexpected value to be output? Wouldn't it produce a "stretch" rather than a "glitch"?

I don't think this can be solved without seeing substantial portion of the code.

JW

[HBesi.1]

The code is simple I load values of a cosine table into the DMA buffer. My first thought was that the DAC hit its limit regarding speed. 80kHz maybe too fast.

[Piranha]

Is D-cache turned on? Is it managed properly?

[waclawek.jan]

Isn't the first or last value in the calculated array off? Read it out and check.

JW

[HBesi.1]

The solution for the problem was changing the callback functions to:

void HAL_ADC_ConvHalfCpltCallback(ADC_HandleTypeDef* hadc)

{

//first half of adc is full

inbufPtr= &adc_val[0];

outbufPtr= &dac_val[0];

processDSP();

}

void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)

{

inbufPtr= &adc_val[DATASIZE];

outbufPtr= &dac_val[DATASIZE];

processDSP();

}

cant really tell why this solved the problem. Occasionally it still happens that 1 sample is pulled high but it can be tolerated.