Depende del micro. Hay micros que permite DMA entre periféricos, sin pasar por RAM (LPC1769, um10360.pdf, p588, s 34.1.1)
Saludos!
Vi el datasheet, lo que si:
The DMA controller allows peripheral-to memory, memory-to-peripheral, and memory-to-memory transactions.
el peripheral-to peripheral , imagino que lo hace peripheral-to memory y memory-to-peripheral como en un solo paso
31.4.1 DMA controller functional description
The DMA Controller enables peripheral-to-memory, memory-to-peripheral,
peripheral-to-peripheral, and memory-to-memory transactions. Each DMA stream
provides unidirectional serial DMA transfers for a single source and destination. For
example, a bidirectional port requires one stream for transmit and one for receive. The
source and destination areas can each be either a memory region or a peripheral, and
can be accessed through the AHB master. Figure 134 shows a block diagram of the DMA
Controller.
"User manual Rev. 3 — 19 December 2013"
Saludos!