CS5530 datasheet(116/241 Pages) NSC

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Revision 4.1

Functional Description (Continued)

3.7.1.2

Physical Region Descriptor Table Address

Before the bus master starts a master transfer it must be

programmed with a pointer (PRD Table Address Register)

to a Physical Region Descriptor Table. This pointer sets

the starting memory location of the Physical Region

Descriptors (PRDs). The PRDs describe the areas of

memory that are used in the data transfer. The descriptor

table entries must be aligned on a 4-byte boundary and

the table cannot cross a 64 KB boundary in memory.

3.7.1.3

Physical Region Descriptor Format

Each physical memory region to be transferred is

described by a Physical Region Descriptor (PRD) as illus-

trated in Table 3-64. When the bus master is enabled

(Command Register bit 0 = 1), data transfer proceeds until

each PRD in the PRD table has been transferred. The bus

master does not cache PRDs.

The PRD table consists of two DWORDs. The first

DWORD contains a 32-bit pointer to a buffer to be trans-

ferred. The second DWORD contains the size (16 bits) of

the buffer and flags (EOT, EOP, JMP). The description of

the flags are as follows:

• EOT bit - If set in a PRD, this bit indicates the last entry

in the PRD table (bit 31). The last entry in a PRD table

must have either the EOT bit or the JMP bit set. A PRD

can not have both the JMP and EOT bits set.

• EOP bit - If set in a PRD and the bus master has

completed the PRD’s transfer, the End of Page bit is

set (Status Register bit 0 = 1) and an SMI is generated.

If a second EOP is reached due to the completion of

another PRD before the End of Page bit is cleared, the

Bus Master Error bit is set (Status Register bit 1 = 1)

and the bus master pauses. In this paused condition,

reading the Status Register clears both the Bus Master

Error and the End of Page bits and the bus master

continues.

• JMP bit - This PRD is special. If set, the Memory

Region Physical Base Address is now the target

address of the JMP. There is no data transfer with this

PRD. This PRD allows the creation of a looping mecha-

nism. If a PRD table is created with the JMP bit set in

the last PRD, the PRD table does not need a PRD with

the EOT bit set. A PRD can not have both the JMP and

EOT bits set.

Table 3-64. Physical Region Descriptor Format

DWORD

Byte 3

Byte 2

Byte 1

Byte 0

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9

Memory Region Base Address [31:1] (Audio Data Buffer)

Reserved

Size [15:1]

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