15

0h

RO

Reserved (RSVD_​M)

Reserved.

14:12

0h

RO

Max Read Request Size (MRRS)

Hardwired to 0.

This field applies only to the PCIe link interface. A separate register is defined for the IOSF interface.

11

0h

RO

Enable No Snoop (ENS)

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

10

0h

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

0h

RO

Phantom Functions Enable (PFE)

Not supported

8

0h

RO

Extended Tag Field Enable (ETFE)

Not supported

7:5

1h

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.

000b: 128 bytes max payload size.

001b: 256 bytes max payload size.

010b: 512 bytes max payload size.

011b: 1024 bytes max payload size.

100b: 2048 bytes max payload size.

101b: 4096 bytes max payload size.

110b: Reserved.

111b: Reserved.

This field applies only to the PCIe link interface. A separate register is defined for the IOSF 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.

Register Attribute: Static.

4:0

0h

RO

Reserved