15

0h

RO

Reserved

14:13

0x0

RW

Optimized Buffer Flush/Fill Enable (OBFFEN)

Optimized Buffer Flush/Fill Enable (OBFFEN):
00b Disable OBFF mechanism.
01b Enable OBFF mechanism using Message signaling (Variation A).
10b Enable OBFF mechanism using Message signaling (Variation B).
11b Enable OBFF using WAKE# signaling.
Note: Only encoding 00b and 11b are supported. The encoding of 01b or 10b would be aliased to 00b.
If DCAP2.OBFFS is clear, programming this field to any non-zero values will have no effect.

12

0x0

RW/V2

10-Bit Tag Requester Enable (PX10BTRE)

This bit, in combination with the Extended Tag Field Enable bit in the Device Control register, determines how many Tag field bits a Requester is permitted to use. When the 10-Bit Tag Requester Enable bit is Set, the Requester is permitted to use 10-Bit Tags.
Software should not change the value of this bit while the Function has outstanding Non-Posted Requests. Otherwise, the result is undefined.
Functions that do not implement 10-Bit Tag Requester capability must hardwire this bit to 0b.

11

0h

RO

Reserved

10

0x0

RW

LTR Mechanism Enable (LTREN)

When Set to 1b, this bit enables the Latency Tolerance Reporting (LTR) mechanism.
For Downstream Ports, this bit must be reset to the default value if the Port goes to DL_​Down status.
If DCAP2.LTRMS is clear, programming this field to any non-zero values will have no effect.

9:8

0h

RO

Reserved

7

0x0

RW

AtomicOp Egress Blocking (AEB)

Applicable and mandatory for Switch Upstream Ports, Switch Downstream Ports, and Root
Ports that implement AtomicOp routing capability - otherwise must be hardwired to 0b.
When this bit is Set, AtomicOp Requests that target going out this Egress Port must be blocked.

6

0x0

RW

AtomicOp Requester Enable (ARE)

Applicable only to Endpoints and Root Ports - must be hardwired to 0b for other Function types. The Function is allowed to initiate AtomicOp Requests only if this bit and the Bus Master Enable bit in the Command register are both Set.
This bit is required to be RW if the Endpoint or Root Port is
capable of initiating AtomicOp Requests, but otherwise is
permitted to be hardwired to 0b.
This bit does not serve as a capability bit. This bit is permitted to be RW even if no AtomicOp Requester capabilities are supported by the Endpoint or Root Port.

5

0x0

RW

ARI Forwarding Enable (AFE)

When set, the Downstream Port disables its traditional Device Number field being 0b enforcement when turning a Type 1 Configuration Request into a Type 0 Configuration Request, permitting access to Extended Functions in an ARI Device immediately below the Port.

4

0x0

RW

Completion Timeout Disable (CTD)

When set to 1b, this bit disables the Completion Timeout mechanism.
This field is required for all devices that support the Completion Timeout Disable Capability.
Software is permitted to set or clear this bit at any time. When
set, the Completion Timeout detection mechanism is disabled.
If there are outstanding requests when the bit is cleared, it is permitted but not required for hardware to apply the completion timeout mechanism to the outstanding requests. If this is done, it is permitted to base the start time for each request on either the time this bit was cleared or the time each request was issued.

3:0

0x0

RW

Completion Timeout Value (CTV)

In Devices that support Completion Timeout programmability, this field allows system software to modify the Completion Timeout value. This field is applicable to Root Ports, Endpoints that issue requests on their own behalf, and PCI Express to PCI/PCI-X Bridges that take ownership of requests issued on PCI Express. For all other devices this field is reserved and must be hardwired to 0000b.
A Device that does not support this optional capability must hardwire this field to 0000b and is required to implement a timeout value in the range 50us to 50ms. Devices that support Completion Timeout programmability must support the values given below corresponding to the programmability ranges indicated in the Completion Timeout Values Supported field.
The Root Port targeted configurable ranges are listed below, along with the range allowed by the PCI Express 2.0 specification.
Defined encodings:
0000b Default range: 40-50ms (spec range 50us to 50ms)
Values available if Range A (50us to 10 ms)
programmability range is supported:
0001b 90-100us (spec range is 50us to 100us)
0010b 9-10ms (spec range is 1ms to 10 ms)
Values available if Range B (10ms to 250ms)
programmability range is supported:
0101b 40-50ms (spec range is 16ms to 55ms)
0110b 160-170ms (spec range is 65ms to 210ms)
Values available if Range C (250ms to 4s)
programmability range is supported:
1001b 400-500ms (spec range is 260ms to 900ms)
1010b 1.6-1.7s (spec range is 1s to 3.5s)
Values not defined above are Reserved.
Software is permitted to change the value in this field at any time. For requests already pending when the Completion Timeout Value is changed, hardware is permitted to use either the new or the old value for the outstanding requests, and is permitted to base the start time for each request either on when this value was changed or on when each request was issued.