CDA CD 60 Especificações descarregar pdf (Página 73)

PCI CD and PCI CDa

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

Template: edt.dot

Page 73

Address Bits

31 16 15 0

0xCC remote Xilinx data

0xC8 PCI interrupt status

0xC4 PCI interrupt and remote Xilinx configuration

0x84 not used flash ROM data

0x80 flash ROM address

0x20 not used

0x1C scatter-gather DMA next count and control

0x18 scatter-gather DMA current count and control

0x14 scatter-gather DMA next address

0x10 scatter-gather DMA current address

0x0C main DMA next count and control

0x08 main DMA current count and control

0x04 main DMA next address

0x00 main DMA current address

3 2 1 0

Byte Word

1 0

Table 14. PCI Local Bus Addresses

Scatter-gather DMA

PCI Direct Memory Access (DMA) devices in Intel-based computers access memory using physical

addresses. Because the operating system uses a memory manager to connect the user program to

memory, memory pages that appear contiguous to the user program are actually scattered throughout

physical memory. Because DMA accesses physical addresses, a DMA read operation must gather data

from noncontiguous pages, and a write must scatter the data back to the appropriate pages. The EDT

Product driver uses information from the operating system to accomplish this. The operating system

passes the driver a list of the physical addresses for the user program memory pages. With this

information, the driver builds a scatter-gather (SG) table, which the DMA device uses sequentially.

Most other PCI computers offer memory management for the PCI bus as well, so the operating system

needs to pass only the address and count for DMA. The addresses appear contiguous to the PCI bus.

1 2 ... 68 69 70 71 72 73 74 75 76 77 78 ... 90 91

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CDA CD 60 Especificações Página 73