For any type of DMA transfer, one needs to provide source and destination addresses, as well as the number of words to transfer. In the case of a peripheral DMA, the peripheral's FIFO serves as either the source or the destination. When the peripheral serves as the source, a memory location (internal or external) serves as the destination address. When the peripheral serves as the destination, a memory location (internal or external) serves as the source address.
With a peripheral DMA, we specify either the source or the destination, depending on the direction of the transfer. In others words, a DMA transfer requires suitable memory mappings. This is what we will discuss in the following sections.
