D M A m o d u l e

DMA module

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.

 

DMA channel

DMA

 

 

arbiter

 

Channel

context RAM

 

transfer

DMA control

128 x 32

attributes

 

 

state machine

 

 

 

 

 

 

 

Data

Data

 

 

in

out

 

Bus interface

 

 

BBus

 

 

 

Figure 15: DMA controller block diagram

The DMA controller arbiter determines which channel the state machine currently is operating.

Fly-by operation transfers

There are two modes of fly-by operation:

Read mode. Transfers data from memory to a peripheral device. Write mode. Transfers data from a peripheral device to memory.

When configured for fly-by operation, the DMA controller transfers data between one of the NS7520 internal peripherals and a memory location. The DMA controller does

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Digi NS7520 manual DMA module, Fly-by operation transfers