Datasheet

82 Datasheet

4.8.28 AGPCTRL – AGP Control Register (Device #0)

Address Offset: B0–B1h

Default Value: 0000h

Access: Read/Write

Size: 16 bits

This register provides for additional control of the AGP interface.

Bit 7 is visible to the operating system and must be retained in this position.

Bit Description

15:8 Reserved

7 GTLB Enable (and GTLB Flush Control).

NOTE: This bit can be changed dynamically (i.e., while an access to GTLB occurs).

This bit must not be changed through memory mapped configuration register access space.

6:0 Reserved

4.8.29 AFT – AGP Functional Test Register (Device #0)

Address Offset: B2–B3h

Default Value: E9F0h

Access: Read/Write, Read/WriteClear

Size: 16 bits

This register provides for additional control of the AGP interface.

Bit Description

15:11 Retry Timer Time-Out Count (RTTOC): These bits control the retry time-out period (for initial data

phase) for the purpose of enhancing the system testability. These bits correspond to value loaded into

retry timer. Default value is 11101b (29d) for retry clock count of 32d (value +3).

10 PCI Write Streaming Disable (PCIBWSD): When this bit is set to ‘1’, PCI_B writes to DDR SDRAM

are disconnected at a 32 byte cache line boundary (write streaming is disabled). When this bit is set to

‘0’ (default), write streaming is enabled.

9 PCI Read Buffer Disable.

1 = When set to “1” the PCI Read Buffering mechanism is disabled. In this mode all data prefetched

and buffered for a PCI to DDR SDRAM read will be discarded when that read transaction terminates.

This bit defaults to “0”.

8:4 AGP/PCI1 Discard Timer Time-out Count. These bits control the length of AGP/PCI1 Delayed

Transaction discard time-out for the purpose of enhancing the system testability. Default value is

11111b (31d) for a discard count of 1024d ((value+1)*32).

3 PCI_B Write Combining Disable (PCIBWCD): When this bit is set to ‘1’, write combining is disabled

for host bus writes targeting the PCI_B bus (depends on configuration). When this bit is ‘0’ (default),

write combining is enabled.