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SAMD21 and DMA: why do I have to give the end address of the DMA buffer, not the start address?

Jan Cumps

I'm checking out a few DMA ADC examples for the Arduino MKR with SAMD21 mcu.

Both examples I reviewed (1 and 2) set the destination buffer's end as the destination address:

#define SAMPLE_NO 8  // Define the number of ADC samples

uint16_t adcResult[SAMPLE_NO] = {};  // Store ADC values

// ..
  descriptor.dstaddr = (uint32_t)&adcResult[0] + sizeof(uint16_t) * SAMPLE_NO;  // Place it in the adcResult array

Most controllers I work with expect the start of the buffer. I'm reading the datasheet's DMA section, haven't found the explanation yet.
Anyone here in the know?