Datasheet

Classic PCI Configuration Space
61
March 5 2007 − June 2011 SCPS154C
4.50 Device Control Register
The device control register controls PCI Express device specific parameters. See Table 4−26 for a complete
description of the register contents.
PCI register offset: 98h
Register type: Read-only, Read/Write
Default value: 2800h
BIT NUMBER 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RESET STATE 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0
Table 4−26. Device Control Register Description
BIT FIELD NAME ACCESS DESCRIPTION
15 CFG_RTRY_ENB RW
Configuration retry status enable. When this read/write bit is set to 1b, the bridge returns a
completion with completion retry status on PCI Express if a configuration transaction forwarded
to the secondary interface did not complete within the implementation specific time-out period.
When this bit is set to 0b, the bridge does not generate completions with completion retry status
on behalf of configuration transactions. The default value of this bit is 0b.
14:12 MRRS RW
Maximum read request size. This field is programmed by host software to set the maximum size
of a read request that the bridge can generate. The bridge uses this field in conjunction with the
cache line size register (offset 0Ch, see Section 4.6) to determine how much data to fetch on a
read request. This field is encoded as:
000 = 128B
001 = 256B
010 = 512B (default)
011 = 1024B
100 = 2048B
101 = 4096B
110 = Reserved
111 = Reserved
11 ENS RW
Enable no snoop. Controls the setting of the no snoop flag within the TLP header for upstream
memory transactions mapped to any traffic class mapped to a virtual channel (VC) other than
VC0 through the upstream decode windows.
0 = No snoop field is 0b
1 = No snoop field is 1b (default)
10
k
APPE RW
Auxiliary power PM enable. This bit has no effect in the bridge.
0 = AUX power is disabled (default)
1 = AUX power is enabled
9 PFE R
Phantom function enable. Since the bridge does not support phantom functions, this bit is
read-only 0b.
8 ETFE R
Extended tag field enable. Since the bridge does not support extended tags, this bit is read-only
0b.
7:5 MPS RW
Maximum payload size. This field is programmed by host software to set the maximum size of
posted writes or read completions that the bridge can initiate. This field is encoded as:
000 = 128B (default)
001 = 256B
010 = 512B
011 = 1024B
100 = 2048B
101 = 4096B
110 = Reserved
111 = Reserved
4 ERO R
Enable relaxed ordering. Since the bridge does not support relaxed ordering, this bit is read-only
0b.
kThis bit is sticky and must retain its value when the bridge is powered by V
AUX
.
Not Recommended for New Designs