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DMA does not work properly with LPC4088 (QSB)

Question asked by shogo matsubara on Dec 20, 2019
Latest reply on Dec 27, 2019 by Felipe García

LPC4088 QSB is used.

I want to acquire 128 samples each using DMA at a sampling rate of 16kHz.

 

I have two problems now.

 

Problem 1:

1kHz analog input is A / D converted and acquired by DMA.A clean waveform can be obtained when the ADC rate is set to 400 kHz, but if the rate is set to 1 kHz, the waveform will be very noisy.

This does not happen when polling and interrupts are used.

 

Problem 2:

When the DMA transfer size is set to 1 and 128, etc., the waveform obtained by DMA is different even if the same analog waveform is input.

 

(D / C conversion and seeing waveform with oscilloscope)

 

The source code uses periph_adc of the following sample code.

https://www.nxp.com/design/microcontrollers-developer-resources/lpcopen-libraries-and-examples/lpcopen-software-development-platform-lpc40xx:LPCOPEN-SOFTWARE-FOR-LPC40XX

 

Thank you.

lpc4088 qsb lpcxpresso lpc4088

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