PCI Component Configuration Access Data, Idsel

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.

24 23

16 15

11 10

0 [1]

Reserved

Bus

Device

Function

Number

Index

AD31..0	IDSEL	(only one signal line asserted)	Function	Register
(w/Type 0	IDSEL	(only one signal line asserted)	Number	Index
(w/Type 0			Number	Index
Config. Cycle)
Config. Cycle)

NOTES:

[1]Bits <1,0> : 00 = Type 0 Cycle, 01 = Type 1 cycle Type 1 cycle only. Reserved on Type 0 cycle.

Figure 4-2.Configuration Cycle

Table 4-1 shows the standard configuration access data for components and slots residing on a PCI bus.

Table 4-1.PCI Device Configuration Access Data

Table 4-1.