Intel B940 Datasheet download pdf (Page 192)

Processor Configuration Registers

192 Datasheet, Volume 2

30 WO 0b

Set Root Table Pointer (SRTP)

Software sets this field to set/update the root-entry table pointer used by

hardware. The root-entry table pointer is specified through the Root-entry Table

Address register. Hardware reports the status of the root table pointer set

operation through the RTPS field in the Global Status register.

The root table pointer set operation must be performed before enabling or re-

enabling (after disabling) DMA-remapping hardware.

After a root table pointer set operation, software must globally invalidate the

context cache followed by global invalidate of IOTLB. This is required to ensure

hardware uses only the remapping structures referenced by the new root table

pointer, and not any stale cached entries.

While DMA-remapping hardware is active, software may update the root table

pointer through this field. However, to ensure valid in-flight DMA requests are

deterministically remapped, software must ensure that the structures

referenced by the new root table pointer are programmed to provide the same

remapping results as the structures referenced by the previous root table

pointer.

Clearing this bit has no effect. The value returned on read of this field is

undefined.

29 W 0b

Set Fault Log (SFL)

This field is valid only for implementations supporting advanced fault logging. If

advanced fault logging is not supported, writes to this field are ignored.

Software sets this field to request hardware to set/update the fault-log pointer

used by hardware. The fault-log pointer is specified through Advanced Fault Log

Hardware reports the status of the fault log set operation through the FLS field

in the Global Status register.

The fault log pointer must be set before enabling advanced fault logging

(through EAFL field). Once advanced fault logging is enabled, the fault log

pointer may be updated through this field while DMA-remapping hardware is

active.

Clearing this bit has no effect. The value returned on read of this field is

undefined.

28 W 0b

Enable Advanced Fault Logging (EAFL)

This field is valid only for implementations supporting advanced fault logging. If

advanced fault logging is not supported, writes to this field are ignored.

Software writes to this field to request hardware to enable or disable advanced

fault logging.

0 = Disable advanced fault logging. In this case, translation faults are reported

through the Fault Recording registers.

1 = Enable use of memory-resident fault log.

When enabled, translation faults are recorded in the memory-resident log. The

fault log pointer must be set in hardware (through SFL field) before enabling

advanced fault logging.

Hardware reports the status of the advanced fault logging enable operation

through the AFLS field in the Global Status register. Value returned on read of

this field is undefined.

27 WO 0b

Write Buffer Flush (WBF)

This bit is valid only for implementations requiring write buffer flushing. If write

buffer flushing is not required, writes to this field are ignored.

Software sets this field to request hardware to flush the root-complex internal

write buffers. This is done to ensure any updates to the memory-resident DMA-

remapping structures are not held in any internal write posting buffers. Refer to

the VTd specification for details on write-buffer flushing requirements.

Hardware reports the status of the write buffer flushing operation through the

WBFS field in the Global Status register.

Clearing this bit has no effect.

Value returned on read of this field is undefined.

B/D/F/Type: 0/0/0/VC0PREMAP

Address Offset: 18–1Bh

Reset Value: 00000000h

Access: W, WO, RO

Bit Attr

Reset

Value

Description

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Intel B940 Datasheet Page 192

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