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34
Intel
82865G/82865GV GMCH Datasheet
Signal Description
2.5.2
AGP Flow Control Signals
NOTE:
1. The term
(2.0)
following a signal name indicates its function in AGP 2.0 signaling mode (1.5 V swing).
2. The term
(3.0)
following a signal name indicates its function in AGP 3.0 signaling mode (0.8 V swing).
2.5.3
AGP Status Signals
Signal Name
Type
Description
GRBF#
(2.0)
GRBF
(3.0)
I
AGP
Read Buffer Full:
This signal indicates if the master is ready to accept previously
requested low priority read data. When GRBF(#) is asserted, the GMCH is not
allowed to return low priority read data to the AGP master on the first block.
GRBF(#) is only sampled at the beginning of a cycle.
If the AGP master is always ready to accept return read data, then it is not required
to implement this signal.
GWBF#
(2.0)
GWBF
(3.0)
I
AGP
Write Buffer Full:
This signal indicates if the master is ready to accept Fast Write
data from the GMCH. When GWBF(#) is asserted, the GMCH is not allowed to
drive Fast Write data to the AGP master. GWBF(#) is only sampled at the
beginning of a cycle.
If the AGP master is always ready to accept fast write data, then it is not required
to implement this signal.
Signal Name
Type
Description
GST[2:0]
(2.0)
GST[2:0]
(3.0)
O
AGP
Status:
These signals provides information from the arbiter to an AGP Master on
what it may do. GST[2:0] only have meaning to the master when its GGNT(#) is
asserted. When GGNT(#) is deasserted, these signals have no meaning and
must be ignored.
GST[2:0] are always an output from the GMCH and an input to the master.
Encoding
Meaning
000
Previously requested low priority read data (Async read for AGP
3.0 Signaling mode) is being returned to the master.
001
Previously requested high priority read data is being returned to
the master. Reserved in AGP 3.0 signaling mode.
010
The master is to provide low priority write data (Async write for
AGP 3.0 signaling mode) for a previously queued write command.
011
The master is to provide high priority write data for a previously
queued write command. Reserved in AGP 3.0 signaling mode.
100
Reserved.
101
Reserved.
110
Reserved.
111
The master has been given permission to start a bus transaction.
The master may queue AGP requests by asserting GPIPE#
(4X signaling mode) or start a PCI transaction by asserting
GFRAME(#).