Digi NS9750 - Manual (Page 526)

A b o u t t h e B B u s D M A c o n t r o l l e r s
5 0 2 N S 9 7 5 0 H a r d w a r e R e f e r e n c e
About the BBus DMA controllers
There are two BBus DMA controllers. One DMA controller supports all BBus peripherals
except the USB device; the other DMA controller is dedicated to the USB device
interface (see the USB Controller Module chapter for more information). Each DMA
controller contains 16 channels, and each DMA channel moves data between external
memory and internal peripherals in fly-by mode, minimizing CPU intervention.
Figure 82 shows the data flow for fly-by DMA transfers.
Figure 82: DMA fly-by transfers
Note:
Neither memory-to-memory transfers nor DMA transfers to external
peripherals are supported.
Each DMA controller has a state machine and a block of static RAM, referred to as
context RAM.
The context RAM contains the current state of each DMA channel.
The single state machine supports all DMA channels in parallel, by context-
switching from channel to channel.
External
Memory
DMA
Channel
Peripheral
Data
DMA ACK
BBUS to AHB MemIF
ADR/CTL