CDA CD 60 Especificaciones descargar pdf (Pagina 74)

PCI CD and PCI CDa

Document Number: 008-00965-06 EDT Public Revision: I December 2004

Template: edt.dot

Page 74

The scatter-gather DMA list is stored in memory. The scatter-gather DMA channel copies it as required

into the main DMA registers. The format of the DMA list in memory is as follows (illustrated in Figure

1):

Each page entry takes eight bytes. Therefore, the scatter-gather DMA count is always evenly divisible

by eight.

The first word consists of the 32-bit start address of a memory page.

The most significant 16 bits of the second word contain control data.

The least significant 16 bits of the second word contain the count.

As of the current release, only bit 16 contains control information. When set to one, and when enabled

by setting bit 28 of the Scatter-gather DMA Next Count and Control register, this bit causes the main

DMA interrupt to be set when the marked page is complete.

Bits

63 32 31 16 0

Each entry

address control (unused) DMA int count

Table 15. Scatter-gather DMA List Format

Performing DMA

All main DMA registers are read-only. Only the corresponding scatter-gather DMA registers must

write to them. To initiate a DMA transfer:

1. Set up one or more scatter-gather DMA lists in host memory, using the format described above and

illustrated in Figure 6.

2. Write the address of the first entry in the list to the Scatter-gather Next DMA Address register.

3. Write the length of the scatter-gather DMA list to the Scatter-gather Next DMA Count and Control

the DMA.

4. If the DMA list is greater than one page, load the address of the first entry of the next page and its

length, as described in steps 2 and 3, when bit 29 of the Scatter-gather Next DMA Count and

Control register is asserted.

Main DMA Current Address Register

Size 32-bit

I/O read-only

Address 0x00

Access EDT_DMA_CUR_ADDR

Comments Automatically copied from the main DMA next address register after main

DMA completes.

1 2 ... 69 70 71 72 73 74 75 76 77 78 79 ... 90 91

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CDA CD 60 Especificaciones Pagina 74