Accelerated Graphics Port Interface Specification

AGP3.0 Interface Specification
Rev. 1.0
29
2.1.5.1 AGP Connector Pins for DBI
On the AGP connector, DBI_LO is assigned the pin B14 (reserved in AGP2.0 specification), and DBI_HI
is assigned the pin A12 (used for PIPE# in AGP2.0 specification). The implication of using A12 for DBI_HI
is that in designs that are “universal” and can operate in AGP2.0 or AGP3.0 modes, both the Master and
Target must multiplex PIPE# and DBI_HI on the same wire. However, for a given mode of operation
(AGP2.0 or AGP3.0), the meaning of this shared wire is fixed after power-up configuration. Such
multiplexing is possible only because PIPE# is not used in AGP3.0, and DBI is not used in AGP2.0.
2.1.5.2 Parity Generation and DBI
During FRAME based PCI transfers, the signal PAR reflects even parity across AD[31:0] and C#/BE[3:0].
During these transfers, the transmitter generates parity before the application of DBI on AD[31:00]. The
receiver checks parity only after performing any data inversion on AD[31:00] required by the assertion of
DBI_HI and DBI_LO.
2.2 Summary of Interfaces
The signal pins defined by AGP3.0 may be used to perform PCI or AGP transactions. Each signal may
be required, optional, or not applicable, depending on the type of device (graphics or core-logic), which
interface (PCI or AGP) is supported, and the type of agent (Master or Target). Table 9 is a summary of
the capability supported by function and agent. Table 10 also includes a summary of the PCI signals
supported by function and agent.
Table 11 is a summary of the AGP3.0 signals supported by function and agent. For example, the
second column represents a graphics agent that supports the PCI interface as a Target. The Support
column indicates whether the interface is required or optional. For example, a graphics agent requires
the PCI target interface. The gray boxes indicate that the signal is not applicable to the function.
Table 9: Summary of Interfaces Based on Function and Agent
Device Graphics Core-logic
Interface PCI AGP3.0 PCI AGP3.0
Agent
Target Master Master
FW
Target
Target Master Target
FW
Master
Support
R O O O R R R O
Legend:
R = Required
O = Optional