PCI-to-PCI Bridge Registers (D30:F0)
11.1.23 BPC—Bridge Policy Configuration Register
(PCI-PCI—D30:F0)
Offset Address: 4Ch–4Fh
Attribute:
Size:
R/W
32 bits
Default Value:
00001200h
Bit
Description
31:14 Reserved
Upstream Read Latency Threshold (URLT) — R/W: This field specifies the number
of PCI clocks after internally enqueuing an upstream memory read request at which
point the PCI target logic should insert wait states in order to optimize lead-off latency.
When the master returns after this threshold has been reached and data has not
arrived in the Delayed Transaction completion queue, then the PCI target logic will
insert wait states instead of immediately retrying the cycle. The PCI target logic will
insert up to 16 clocks of target initial latency (from FRAME# assertion to TRDY# or
STOP# assertion) before retrying the PCI read cycle (if the read data has not arrived
yet).
13:8
Note that the starting event for this Read Latency Timer is not explicitly visible
externally.
A value of 0h disables this policy completely such that wait states will never be inserted
on the read lead-off data phase.
The default value (12h) specifies 18 PCI clocks (540 ns) and is approximately 4 clocks
less than the typical idle lead-off latency expected for desktop ICH10 systems. This
value may need to be changed by BIOS, depending on the platform.
Subtractive Decode Policy (SDP) — R/W.
0 = The PCI bridge always forwards memory and I/O cycles that are not claimed by any
other device on the backbone (primary interface) to the PCI bus (secondary
interface).
1 = The PCI bridge will not claim and forward memory or I/O cycles at all unless the
corresponding Space Enable bit is set in the Command register.
NOTE: The Boot BIOS Destination Selection strap can force the BIOS accesses to PCI.
CMD.MSE
BPC.SDP
Range
Forwarding Policy
7
Forward unclaimed
cycles
0
0
1
0
1
X
Don’t Care
Don’t Care
Within range
Forwarding Prohibited
Positive decode and
forward
Subtractive decode &
forward
1
X
Outside
PERR#-to-SERR# Enable (PSE) — R/W. When this bit is set, a 1 in the PERR#
Assertion status bit (in the Bridge Proprietary Status register) will result in an internal
SERR# assertion on the primary side of the bridge (if also enabled by the SERR#
Enable bit in the primary Command register). SERR# is a source of NMI.
6
Secondary Discard Timer Testmode (SDTT) — R/W.
0 = The secondary discard timer expiration will be defined in BCTRL.SDT (D30:F0:3E,
5
bit 9)
1 = The secondary discard timer will expire after 128 PCI clocks.
4:3
Reserved
Datasheet
369
INTEL [ INTEL ]
