During FRAME# Operation: G_FRAME# is an output when the GMCH acts as an initiator on the AGP Interface. G_FRAME# is asserted by the GMCH to indicate the
beginning and duration of an access. G_FRAME# is an input when the GMCH acts as a FRAME#-based AGP target. As a FRAME#-based AGP target, the GMCH latches the C/BE[3:0]# and the AD[31:0] signals on the first clock edge on which
GMCH samples FRAME# active.

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5.2 Intel 855GM/GME North Bridge(5)

AGP/PCI Signals-Semantics Descriptions

AGP Strobe Descriptions

Signal Name

Type

Description

Signal Name

Type

Description

GFRAME#

I/O

G_FRAME: Frame.

GADSTB[0]

I/O

Address/Data Bus Strobe-0:provides timing for 2x and 4x data on

 

AGP

During PIPE# and SBA Operation: Not used by AGP SBA and

 

AGP

AD[15:0] and C/BE[1:0]# signals. The agent that is providing the

 

 

PIPE# operations.

 

 

data will drive this signal.

 

 

During Fast Write Operation: Used to frame transactions as an

GADSTB#[0]

I/O

Address/Data Bus Strobe-0 Complement: With AD STB0, forms a

 

 

output during Fast Writes.

 

AGP

differential strobe pair that provides timing information for the

 

 

 

 

 

AD[15:0] and C/BE[1:0]# signals. The agent that is providing the

 

 

 

 

 

data will drive this signal.

GIRDY#

I/O

 

AGP

acts as a FRAME#-based AGP target. The assertion of G IRDY#

 

GADSTB[1]

I/O

Address/Data Bus Strobe-1:Provides timing for 2x and 4x data on

 

Document

 

 

 

Secret

AGP

AD[31:16] and C/BE[3:2]# signals. The agent that is providing the

 

 

 

 

 

 

data will drive this signal.

 

 

 

 

GADSTB#[1]

I/O

Address/Data Bus Strobe-1 Complement: With AD STB1, forms a

 

 

 

 

 

AGP

differential strobe pair that provides timing information for the

G_IRDY#: Initiator Ready.

 

 

 

 

 

AD[15:0] and C/BE[1:0]# signals in 4X mode. The agent that is

 

 

 

 

 

providing the data will drive this signal.

During PIPE# and SBA Operation: Not used while enqueueing

 

GSBSTB

I

Sideband Strobe: Provides timing for 2x and 4x data on the

requests via AGP SBA and PIPE#, but used during the data phase of

 

 

AGP

SBA[7:0] bus. It is driven by the AGP master after the system has

PIPE# and SBA transactions.

MiTac

 

 

been configured for 2x or 4x sideband address mode.

During FRAME# Operation: G_IRDY# is an output when GMCH

 

GSBSTB#

I

Sideband Strobe Complement: The differential complement to the

acts as a FRAME#-based AGP initiator and an input when the GMCH

 

 

AGP

SB STB signal. It is used to provide timing 4x mode.

Confidential

 

 

indicates the current FRAME#-based AGP bus in ator's ability to

 

 

 

 

complete the current data phase of the transaction.

 

 

 

 

During Fast Write Operation: In Fast Write mode, G IRDY#

 

 

 

 

indicates that the AGP-compliant master is ready to provide all write

 

 

 

 

data for the current transaction. Once G IRDY# is ass rt for write

 

 

 

 

operation, the master is not allowed to insert wait stat s. The master is

 

 

 

 

never allowed to insert a wait state during the

n t al ata transfer (32

 

 

 

 

bytes) of a write transaction. However, it may

nsert wait states after

 

 

 

 

each 32-byte block is transferred.

 

 

 

 

 

 

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