CS5530A datasheet(119/259 Pages) NSC

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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 Descrip-

tors (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 3-65. 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.

ThePRD table consists oftwo DWORDs.The firstDWORD

contains a 32-bit pointer to a buffer to be transferred. 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 mechanism. 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 3-65. 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

876543

210

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

Reserved

Size [15:1]

CS5530A Datasheet(PDF) 119 Page - National Semiconductor (TI)

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