Chapter 4 System Support
P dress Register
I/O Port 0CF8h, R/W, (32-bit access only)
PCI Configuration Data Register
I/O Port 0CFCh, R/W, (8-, 16-, 32-bit access)
PCI BUS TRANSACTIONS
The PCI bus consists of a 32-bit path (AD31-00 lines) that uses a multiplexed scheme for
handling both address and data transfers. A bus transaction consists of an address cycle and one
or more data cycles, with each cycle requiring a clock (PCICLK) cycle. High performance is
realized during burst modes in which a transaction with contiguous memory locations requires
CI Configuration Ad
evices on the PC ply wi PCI protoc at allows figurati of that dev
oftware. In th io echani h Bus
tio f a PCI . Th
ddress reg S 8h alue that specifies the PCI bus, PCI
cc e c tion data r ( _D
CFCh contain
Bit
Function it Fun
31 Configuration En
0 = Disabled
1 = Enable
30..24 Reserved - rea
23..16 Bus Number. S I bus
15..11 PCI Device Nu ects PC
device for acc
4.2.1
at only one address cycle be conducted and subsequent data cycles are completed using auto-
cremented addressi
onf p bus).
4.2.1.1 I/O and Memory Cycles
For I/O ecode (AD31..0) for byte-level addressing
is handled by the appropriate PCI device. For memory addressing, PCI devices decode the
essing and check the AD1,0 lines for burst (linear-
incrementing) mode. In burst mode, subsequent data phases are conducted a dword at a time with
4.2.1.2 Configuration Cycles
D I bus must com th ol th con on ice by
s is system, configurat n m sm #1 (as described in t e PCI Local
specification Rev. 2.1) is employed. This method uses two 32-bit registers for initiating a
configuration cycle for accessing the configura n space o device e configuration
a ister (CONFIG_ADDRE S) at 0CF holds a v
device, and specific register to be a essed. Th onfigura registe CONFIG ATA) at
0 s the configuration data.
B ction
able
31..0 Configuration Data.
d/write 0s
elects PC
mber. Sel I
ess
Function Number. Selects function of
e.
7..2
1,0
01 = Type 1
th
in n Four types of d ss n
ecial. A odin but p to vic e I
g. ad re cycl
g is distri
es ca take pl
ed (left u
ace on the P
each de
CI bus; I/
e on th
O, memory,
c iguration, and s ddress dec PC
and memory cycles, a standard 32-bit address d
AD31..2 lines for dword-level addr
addressing assumed to increment accordingly (four bytes at a time).
10..8
selected PCI devic
Register Index. Specifies config. reg.
Configuration Cycle Type ID.
00 = Type 0
Compaq Evo and Workstation Personal Computers
Featuring the Intel Pentium 4 Processor
Second Edition – January 2003
4-4
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