Intel 80312 I/O Companion Chip - ECEE

Intel ® 80312 I/O Companion ChipPCI-to-PCI Bridge Unit4.4.3 Type 1 to Type 1 ForwardingA Type 1 write transaction on the Primary bus is converted to a Type 0 write transaction andforwarded to the Secondary interface provided the following condition is met:• Bus number in the Type 1 command is equal to the Secondary Bus Number Register (SBNR,see Section 4.15).A Type 1 write transaction on the Primary bus is forwarded unmodified to the Secondary interfaceprovided the following condition is met:• Bus number in the Type 1 command is greater than the SBNR but less than or equal to theSubordinate Bus Number Register (SubBNR).In this instance, the Secondary interface will generate a Type 1 command address cycle withexactly the same address information that was contained within the Type 1 command on thePrimary interface. The Type 1 command on the Secondary interface will be intercepted anddecoded by a downstream bridge.A Type 1 write transaction on the Secondary bus is forwarded unmodified to the Primary interfaceprovided all of the following conditions are met:• Device Number is all ones - S_AD[15:11] = 11111 2• Function Number is all ones - S_AD[10:8] =111 2• Register Number is all zeros - S_AD[7:2] = 00000 2• Bus Number does not match the Primary Bus Number of the bridge• Bus Number is outside the range of bus numbers specified by the Secondary Bus Number(inclusive) and the Subordinate Bus Number (inclusive) of the bridge.The bridge will generate a Type 1 on the Primary side with exactly the same information as on theSecondary side. This Type 1 command will be intercepted by an upstream bridge and converted toa Special Cycle transaction.Note that Type 1 to Type 1 forwarding is for Configuration Write commands only. Type 1Configuration Read commands are not forwarded upstream through the bridge.Developer’s Manual 4-11