Initiating a Block Transfer
You can rewrite the DMA channel transfer counter reload only after the next-to-
last frame in the current block transfer it completed. Otherwise, the new reload
values would affect subsequent frame boundaries in the current block transfer.
However, if the frame size is the same for the current and next block transfers,
this restriction is not relevant. See section 5.5 for more explanation of the DMA
channel transfer counter.
Direct Memory Access (DMA) Controller
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