15

0h

RO

Reserved

14:12

0x0

RO

Max Read Request Size (MRRS)

Hardwired to 0.
This field applies only to the PCIe link interface.

11

0x0

RO

Enable No Snoop (ENS)

Not supported. The root port will never issue non-snoop requests.

10

0x0

RW/P

Aux Power PM Enable (APME)

Must be RW for OS testing. The OS will set this bit to 1 if the device connected has detected aux power. It has no effect on the root port otherwise.

9

0x0

RO

Phantom Functions Enable (PFE)

Not supported

8

0x0

RO

Extended Tag Field Enable (ETFE)

Not supported

7:5

0x1

RW

Max Payload Size (MPS)

The root port supports up to 256B max payload.
Programming this field to any values greater than DCAP.MPS will result in aliasing to 128B max payload size.
0: 128 bytes max payload size.
1: 256 bytes max payload size.
2: 512 bytes max payload size.
3: 1024 bytes max payload size.
4: 2048 bytes max payload size.
5: 4096 bytes max payload size.
6: Reserved.
7: Reserved.
This field applies only to the PCIe link interface.
Note: Software should ensure that the system is quiescent and no TLP is in progress prior to changing this field. BIOS should program this field prior to enabling BME.

4

0x0

RO

Enable Relaxed Ordering (ERO)

Not supported

3

0x0

RW

Unsupported Request Reporting Enable (URE)

When set, allows signaling ERR_​NONFATAL, ERR_​FATAL, or ERR_​COR to the Root Control register when detecting an unmasked Unsupported Request (UR).
An ERR_​COR is signaled when a unmasked Advisory Non-Fatal UR is received.
An ERR_​FATAL, ERR_​or NONFATAL, is sent to the Root Control Register when an uncorrectable non-advisory UR is received with the severity set by the Uncorrectable Error Severity register.

2

0x0

RW

Fatal Error Reporting Enable (FEE)

Enables signaling of ERR_​FATAL to the Root Control register due to internally detected errors or error messages received across the link. Other bits also control the full scope of related error reporting.

1

0x0

RW

Non-Fatal Error Reporting Enable (NFE)

When set, enables signaling of ERR_​NONFATAL to the Root Control register due to internally detected errors or error messages received across the link. Other bits also control the full scope of related error reporting.

0

0x0

RW

Correctable Error Reporting Enable (CEE)

When set, enables signaling of ERR_​CORR to the Root Control register due to internally detected errors or error messages received across the link. Other bits also control the full scope of related error reporting.