PCI9080 datasheet(32/133 Pages) ETC

32 / 133 page

SECTION 3

PCI 9080

FUNCTIONAL DESCRIPTION

©PLX Technology, Inc., 1997

Page 24

Version 0.93

3.6.2 Chaining Mode DMA

Chaining DMA operates as follows:

The Host Processor or the Local Processor sets up

descriptor blocks in local or host memory that are

composed of a PCI address, local address, transfer

count, transfer direction and address of the next

descriptor block. The Host or Local Processor then sets

up the address of the initial descriptor block in the

descriptor pointer register of the PCI 9080 and initiates

the transfer by setting a control bit. The PCI 9080 loads

the first descriptor block and initiates the data transfer.

The PCI 9080 continues to load descriptor blocks and

transfer data until it detects the end of chain bit is set in

the next descriptor pointer register. The PCI 9080 can

be programmed to interrupt the local processor by

setting the "Interrupt after Terminal Count" bit or PCI

host upon completion of each block transfer and after all

block transfers are complete (done) (refer to Figure 3-8).

If the chaining descriptors are located in local memory,

the DMA controller can be programmed to clear the

transfer size at the completion of each DMA. (Refer to

"DMA Clear Count Mode").

Note: The DMA descriptor can be on the local memory

or PCI memory, or both (first descriptor on local

memory, and second descriptor on PCI memory).

Set up First Descriptor

Pointer Register

(First only requires

Descriptor Pointer)

First PCI Address

First Memory Block

to Transfer

First Memory Block

to Transfer

Next Memory Block

to Transfer

Next Memory Block

to Transfer

Local or

Host

Memory

PCI Host

Memory

Mode Register

Set DMA Mode

to Chaining

Command/Status Register

Set the Enable and

Go bits in the DMA

Command/Status Register

to Initate DMA Transfer

First Local Address

First Transfer Size (byte count)

Next Descriptor Pointer

Descriptor Pointer Register

PCI Address

Local Address

Transfer Size (byte count)

Next Descriptor Pointer

End of Chain

Specification Bit

Figure 3-8. Chaining DMA Initialization

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