CDA CD 60 Betriebsanweisung PDF herunterladen (Seite 24)

Registers PCI CD/CDa Configurable DMA Interface User’s Guide

20 EDT, Inc. May 2007

Figure 6. 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

PCI CD/CDa 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.

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 7):

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

visible 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.

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.

Address Bits

31 16 15 0

0xCC UI Xilinx data

0xC8 PCI interrupt status

0xC4 PCI interrupt and UI 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

Byte 3 2 1 0

Word 1 0

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 39 40

Kommentare zu diesen Handbüchern

Keine Kommentare

CDA CD 60 Betriebsanweisung Seite 24

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Kochfelder CDA CD 60