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AGP/PCI Signals-Semantics Descriptions (Continued)
Signal Name Type Description
GTRDY#
I/O
AGP
G_TRDY#: Target Ready.
During PIPE# and SBA Operation: Not used while enqueueing
requests via AGP SBA and PIPE#, but used during the data phase of
PIPE# and SBA transactions.
During FRAME# Operation: G_TRDY# is an input when the
GMCH acts as an AGP initiator and is an output when the GMCH
acts as a FRAME#-based AGP target. The assertion of G_TRDY#
indicates the target’s ability to complete the current data phase of the
transaction.
During Fast Write Operation: In Fast Write mode, G_TRDY#
indicates the AGP-compliant target is ready to receive write data for
the entire transaction (when the transfer size is less than or equal to 32
bytes) or is ready to transfer the initial or
subsequent block (32 bytes) of data when the transfer size is greater
than 32 bytes. The target is allowed to insert wait states after each
block (32 bytes) is transferred on write transactions.
GSTOP#
I/O
AGP
G_STOP#: Stop.
During PIPE# and SBA Operation: This signal is not used during
PIPE# or SBA operation.
During FRAME# Operation: G_STOP# is an input when the
GMCH acts as a FRAME#-
b
ased AGP initiator and is an output when
the GMCH acts as a FRAME#-based AGP target. G_STOP# is used
for disconnect, retry, and abort sequences on the AGP interface.
GDEVSEL#
I/O
AGP
G_ DEVSEL#: Device Select.
During PIPE# and SBA Operation: This signal is not used during
PIPE# or SBA operation.
During FRAME# Operation: G_DEVSEL#, when asserted,
indicates that a FRAME#-based AGP target device has decoded its
address as the target of the current access. The GMCH asserts
G_DEVSEL# based on the DDR SDRAM
address range being accessed by a PCI initiator. As an input,
G_DEVSEL# indicates whether the AGP master has recognized a
PCI cycle to it.
GREQ#
I
AGP
G_REQ#: Request.
During SBA Operation: This signal is not used during SBA
operation.
During PIPE# and FRAME# Operation: G_REQ#, when asserted,
indicates that the AGP master is requesting use of the AGP interface
to run a FRAME#- or PIPE#-based operation.
Signal Name Type Description
GGNT#
O
AGP
G_GNT#: Grant.
During SBA, PIPE# and FRAME# Operation: G_GNT#, along
with the information on the ST[2:0] signals (status bus), indicates
how the AGP interface will be used next. Refer to the
AGP Interface
Specification, Revision 2.0
for further explanation
of the ST[2:0] values and their meanings.
GAD[31:0]
I/O
AGP
G_AD[31:0]: Address/Data Bus.
During PIPE# and FRAME# Operation: The G_AD[31:0] signals
are used to transfer both address and data information on the AGP
interface.
During SBA Operation: The G_AD[31:0] signals are used to
transfer data on the AGP interface.
GCBE#[3:0]
I/O
AGP
Command/Byte Enable.
During FRAME# Operation: During the address phase of a
transaction, the G_CBE[3:0]# signals define the bus command.
During the data phase, the G_CBE[3:0]# signals are used as byte
enables. The byte enables determine which byte lanes carry
meaningful data. The commands issued on the G_CBE# signals
during FRAME#-based AGP transactions are the same G_CBE#
command described in the PCI 2.2 specification.
During PIPE# Operation: When an address is enqueued using
PIPE#, the C/BE# signals carry command information. The command
encoding used during PIPE#-based AGP is
different than the
command encoding used during FRAME#-based AGP cycles (or
standard PCI cycles on a PCI bus).
During SBA Operation: These signals are not used during SBA
operation.
GPAR
I/O
AGP
Parity.
During FRAME# Operation: G_PAR is driven by the GMCH when
it acts as a FRAME#-based AGP initiator during address and data
phases for a write cycle, and during the address phase for a read
cycle. G_PAR is driven by the GMCH when it acts as a
FRAME#-based AGP target during each data phase of a
FRAME#-based AGP memory read cycle. Even parity is generated
across G_AD[31:0] and G_CBE[3:0]#.
During SBA and PIPE# Operation: This signal is not used during
SBA and PIPE# operation.
PCIRST# from the ICH4-M is assumed to be connected to RSTIN# and is used to reset AGP interface
logic within the GMCH. The AGP agent will also typically use PCIRST# provided by the ICH4-M as
an input to reset its internal logic.
5.2 Intel 855GM/GME North Bridge(6)
ATP/PCI Signals-Semantics Descriptions(Continued)
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