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32 Intel® 41210 Serial to Parallel PCI Bridge Design Guide
PCI-X Layout Guidelines
Note: PCI Express Assert_INTx/Deassert_INTx messages are not inhibited by the BME bit.
8.1.1 Interrupt Routing for Devices Behind a Bridge
Given the legacy interrupt sharing scheme shown in Table 4, to get the best legacy interrupt
performance (by reducing interrupt sharing), adapter boards have to select the appropriate
A_INTX#, B_INTX# (where X is A, B, C or D) input pin to use on each PCI bus segment. The
chosen interrupt input also imposes a PCI device number requirement for the interrupt source as
specified in the PCI-to-PCI Bridge specification and reproduced in Table 5
.
8.2 PCI Arbitration
The 41210 Bridge supports a high-performance internal PCI arbiter that supports up to seven
masters on each PCI segment A and B PCI Buses. The request inputs into the internal arbiter
include: six external request inputs and 1 internal request input. All request inputs to the internal
arbiter are split into two groups, a high priority group and a low priority group. Any master,
including the internal master, can be programmed to be in either of the two groups. This could also
mean that all the request inputs into the arbiter could be in one single group. Within a group,
priority is round-robin. The entire low-priority group represents one slot in the high priority group.
The 41210 Bridge provides a 16-bit arbiter control register to control two aspects of the internal
arbiter behavior:
Table 5. Interrupt Binding for Devices Behind a Bridge
Device Number on
Secondary Bus
Interrupt Pin on Device Interrupt on 41210 Bridge
-
a
. 4, 8
b
, 12, 16, 20, 24, 28
INTA# INTA#
INTB# INTB#
INTC# INTC#
INTD# INTD#
1, 5, 9
b
, 13, 17, 21, 25, 29
INTA# INTB#
INTB# INTC#
INTC# INTD#
INTD# INTA#
2, 6, 10
b
, 14, 18, 22, 26, 30
INTA# INTC#
INTB# INTD#
INTC# INTA#
INTD# INTB#
3, 7, 11
b
, 15, 19, 23, 27, 31
INTA# INTD#
INTB# INTA#
INTC# INTB#
INTD# INTC#
a. Device number 0 is reserved for the Bridge and should not be assigned to secondary devices.
b. AD[27:24] which correspond to devices 11:8 should not be used for IDSEL# connections as these signals are used
when accessing the extended configuration space in the bridge from the secondary bus.