D M A M o d u l e

Register bit assignment

Bits

Access

Mnemonic

Reset

Description

 

 

 

 

 

D31

R/W

CE

0

DMA channel enable

 

 

 

 

Set only after the other channel mode bits are set.

 

 

 

 

The DMA channel begins reading the first buffer

 

 

 

 

descriptor when CE is set to 1.

 

 

 

 

 

D30

W

CA

0

Channel abort request

 

 

 

 

When set, causes the current DMA operation to

 

 

 

 

complete and the buffer to be closed. CA is not

 

 

 

 

cleared automatically after the requested abort is

 

 

 

 

complete; firmware must clear the bit after

 

 

 

 

recognizing CAIP active.

 

 

 

 

 

D29:28

R/W

BB

0

Bus bandwidth

 

 

 

 

Determines how often the DMA channel can

 

 

 

 

arbitrate for access to the bus.

 

 

 

 

00

100% (no limit) — The DMA channel can

 

 

 

 

 

arbitrate each time.

 

 

 

 

01

75% — The DMA channel can arbitrate 3 out

 

 

 

 

 

of 4 times.

 

 

 

 

10

50% — The DMA channel can arbitrate 2 out

 

 

 

 

 

of 4 times.

 

 

 

 

11

25% — The DMA channel can arbitrate 1 out

 

 

 

 

 

of 4 times.

 

 

 

 

 

D27:26

R/W

MODE

0

DMA operation mode

 

 

 

 

00

Fly-by write (peripheral-to-memory)

 

 

 

 

01

Fly-by read (memory-to-peripheral)

 

 

 

 

10

Memory-to-memory (source-to-destination)

 

 

 

 

11

Reserved

 

 

 

 

Identifies the data transfer mode. Each DMA

 

 

 

 

channel can be configured to operate in either fly-

 

 

 

 

by or memory-to-memory mode.

Table 50: DMA Control register bit definition

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Digi NS7520 manual DMA Control register bit definition, DMA channel enable, Channel abort request, Bus bandwidth