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82815 GMCH
R
24
Datasheet
2.3.
AGP Interface Signals
For more details on the operation of these signals, refer to the AGP Interface Specification Revision 2.0.
Some of the AGP interface signals are multiplexed with Display Cache interface signals. AGP inteface
signals only function as documented in this section when the GMCH AGP interface is enabled (GMCH
integrated graphics disabled). Refer to Section 2.11 for multiplexing map of AGP to Display Cache
interface signals.
2.3.1.
AGP Addressing Signals
There are two mechanisms that the AGP master can enqueue AGP requests: PIPE# and SBA (side-band
addressing). Upon initialization, one of the methods is chosen. The master may not switch methods
without a full reset of the system. When
PIPE#
is used to enqueue addresses, the master is not allowed to
queue addresses using the SBA bus. For example, during configuration time, if the master indicates that
it can use either mechanism, the configuration software will indicate which mechanism the master will
use. Once this choice has been made, the master will continue to use the mechanism selected until the
system is reset (and reprogrammed) to use the other mode. This change of modes is not a dynamic
mechanism but rather a static decision when the device is first being configured after reset.
Signal Name
Type
Description
PIPE#
I
AGP
Pipeline.
During PIPE# Operation.
This signal is asserted by the AGP master to indicate a
full-width address is to be enqueued on by the target using the AD bus. One
address is placed in the AGP request queue on each rising clock edge while PIPE#
is asserted.
During SBA Operation.
This signal is not used if SBA (Side Band Addressing) is
selected.
During FRAME# Operation.
This signal is not used during AGP FRAME#
operation.
SBA[7:0]
I
AGP
Side-band Addressing.
During PIPE# Operation.
These signals are not used during PIPE# operation.
During SBA Operation.
These signals (the SBA, or side-band addressing, bus) are
used by the AGP master (graphics component) to place addresses into the AGP
request queue. The SBA bus and AD bus operate independently. That is,
transactions can proceed on the SBA bus and the AD bus simultaneously.
During FRAME# Operation.
These signals are not used during AGP FRAME#
operation.