Chapter 4 System Support
Two types of configuration cycles are used. A Type 0 (zero) cycle is targeted to a device on the
PCI bus on which the cycle is running. A Type 1 cycle is targeted to a device on a downstream
PCI bus as identified by bus number bits <23..16>. With three or more PCI buses, a PCI bridge
may convert a Type 1 to a Type 0 if it’s destined for a device being serviced by that bridge or it
may forward the Type 1 cycle unmodified if it is destined for a device being serviced by a
downstream bridge. Figure 4-2 shows the configuration cycle format and how the loading of
0CF8h results in a Type 0 configuration cycle on the PCI bus. The Device Number (bits <15..11>
determines which one of the AD31..11 lines is to be asserted high for the IDSEL signal, which
acts as a “chip select” function for the PCI device to be configured. The function number (CF8h,
bits <10..8>) is used to select a particular function within a PCI component.
AD31..0
(w/Type 00
Config. Cycle)
NOTES:
[1] Bits <1,0> : 00 = Type 0 Cycle, 01 = Type 1 cycle
Type 01 cycle only. Reserved on Type 00 cycle.
Results in:
Register 0CF8h
Register
Index
Function
Number
IDSEL (only one signal line asserted)
Bus
Number
122
Register
Index
2 7
Device
Number
1
Function
Number
8 1
1
Reserved
3
1 0 [1]
Figure 4-2. Configuration Cycle
Table 4-1 shows the standard configuration of device numbers and IDSEL connections for
components and slots residing on a PCI bus.
Table 4-1. PCI Device Configuration Access
Table 4-1.
PCI Component Configuration Access
PCI Component
Notes
Function #
Device #
PCI
Bus #
IDSEL
Wired to:
82815 GMCH:
Memory Controller
AGP Bridge
Direct AGP Graphics Cntlr.
0
0
0
0 (00h)
1 (01h)
2 (02h)
0
0
0
--
AGP slot [3] 0 0 (00h) 1 --
82801BA ICH2:
PCI Bridge
LPC Bridge
EIDE Controller
USB I/F #1
SMBus Controller
USB I/F #2
AC97 Audio Controller
AC97 Modem Controller
Network Interface Controller
[1]
[1]
0
0
1
2
3
4
5
6
0
30 (1Eh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
8 (08h)
0
0
0
0
0
0
0
0
2
--
PCI Connector 1 (slot 1) [2] 0 4 (04h) 2 AD24
PCI Connector 2 (slot 2) [2] 0 9 (09h) 2 AD25
PCI Connector 3 (slot 3) [2] 0 10 (0Ah) 2 AD26
PCI Connector 4 (slot 4) [2,3] 0 11 (0Bh) 2 AD27
PCI Connector 5 (slot 5) [2,3] 0 13 (0Dh) 2 AD29
NOTES:
[1] Not implemented.
[2] PCI bus number given is for standard configuration.
[3] Slim Desktop and Configurable Minitower models only.
Compaq Deskpro and Evo Personal Computers
Featuring Intel Celeron and Pentium III Processors
Fifth Edition – March 2002
4-4
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