Copyright 1997-2000, V3 Semiconductor Inc.
EPC User
’
s Manual Revision 1.05
89
Chapter 9
PCI Configuration
The EPC may be used as both a host or target bridge device. As such, the EPC can both
generate configuration cycles and respond to them. This chapter describes both types of
PCI configuration.
9.1
CONFIGURATION AS A SYSTEM HOST BRIDGE
The EPC acts as a host bridge when it is used to configure other PCI devices in the system.
For example, a laser printer that uses an i960
as the main CPU and uses PCI as the
mezzanine bus, would run configuration cycles to initialize PCI peripherals such as ethernet
chips and SCSI controllers.
9.1.1
EPC Host Configuration Mechanism
PCI configuration cycles consist of setting a specified target
’
s IDSEL line active, then
performing reads and writes to the configuration space of the selected peripheral. The
IDSEL line is deasserted after accesses to the target peripheral
’
s configuration space are
complete.
9.1.2
Controlling Target IDSEL Lines
The EPC does not provide a direct control of the state of individual targets
’
IDSEL lines. The
system hardware must provide a mechanism for activating the IDSEL line for each target (if
the EPC is to be used as a host bridge). IDSEL is not like other PCI signals in that it need
not be synchronous with each configuration cycle. IDSEL must be active during the address
phase to select the EPC.
An external register is the simplest method for controlling IDSEL. V3
’
s Am29K
TM
PCI
motherboard (the Lion-29K), for example, uses a PAL device that sets and clears specific
IDSEL lines based on accesses to specific memory locations in local space.