Datasheet

Classic PCI Configuration Space

March 5 2007 − June 2011 SCPS154C

4.52 Link Capabilities Register

The link capabilities register indicates the link specific capabilities of the bridge. See Table 4−28 for a complete

description of the register contents.

PCI register offset: 9Ch

Default value: 0002 XC11h

BIT NUMBER 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

RESET STATE 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0

BIT NUMBER 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

RESET STATE x x x x 1 1 0 0 0 0 0 1 0 0 0 1

Table 4−28. Link Capabilities Register Description

BIT FIELD NAME ACCESS DESCRIPTION

31:24 PORT_NUM R

Port number. This field indicates port number for the PCI Express link. This field is read-only 00h

indicating that the link is associated with port 0.

23:18 RSVD R Reserved. Return 00 0000b when read.

17:15 L1_LATENCY R

L1 exit latency. This field indicates the time that it takes to transition from the L1 state to the L0

state. Bit 6 (CCC) in the link control register (offset A0h, see Section 4.53) equals 1b for a common

clock and equals 0b for an asynchronous clock.

For a common reference clock, the value of this field is determined by bits 20:18

(L1_EXIT_LAT_ASYNC) of the control and diagnostic register 1 (offset C4h, see Section 4.62).

For an asynchronous reference clock, the value of this field is determined by bits 17:15

(L1_EXIT_LAT_COMMON) of the control and diagnostic register 1 (offset C4h, see Section 4.62).

14:12 L0S_LATENCY R

L0s exit latency. This field indicates the time that it takes to transition from the L0s state to the L0

state. Bit 6 (CCC) in the link control register (offset A0h, see Section 4.53) equals 1b for a common

clock and equals 0b for an asynchronous clock.

For a common reference clock, the value of 011b indicates that the L1 exit latency falls between

256 ns to less than 512 ns.

For an asynchronous reference clock, the value of 100b indicates that the L1 exit latency falls

between 512 ns to less than 1 μs.

11:10 ASLPMS R

Active state link PM support. This field indicates the level of active state power management that

the bridge supports. The value 11b indicates support for both L0s and L1 through active state

power management.

9:4 MLW R

Maximum link width. This field is encoded 00 0001b to indicate that the bridge only supports a 1x

PCI Express link.

3:0 MLS R

Maximum link speed. This field is encoded 1h to indicate that the bridge supports a maximum link

speed of 2.5 Gb/s.

Not Recommended for New Designs