I'm wishing to sample audio at 20KHz on a single 16-bit ADC channel. I would like to gather, in RAM, 64 to 128 samples (128B to 256B) before raising an interrupt from the DMA to trigger an FFT. What's the most efficient/effective way (energy and least CPU interruption) to configure the DMA to achieve this?
i.e. Is this a 128 minor loop iteration or 2 minor and 64 major loops scenario etc?