82845G Datasheet, PDF (111/193 Pages) Intel Corporation – Intel 82845G/82845GL/82845GV Graphics and Memory Controller Hub (GMCH)

Functional Description
4.3
4.3.1
4.3.1.1
AGP Interface
See the Accelerated Graphics Port Interface Specification, Revision 2.0 for additional details about
the AGP interface.
Overview
The GMCH multiplexes an AGP interface with two DVO ports. The DVO ports can support single
channel DVO devices or can combine to support dual-channel devices, supporting higher
resolutions and refresh rates. When an external AGP device is used, the multiplexed DVO ports are
not available, as the GMCH’s IGD will be disabled. For more information on the multiplexed DVO
interface, refer to Section 4.5.
The GMCH supports 1.5 V AGP 1X/2X/4X devices. The AGP signal buffers have one mode of
operation; 1.5 V drive/receive (not 3.3 V tolerant). The GMCH supports 4X (266 MT/s) clocking
transfers for read and write data, and sideband addressing. The GMCH has a 32-deep AGP request
queue.
AGP semantic transactions to system SDRAM do not get snooped and are, therefore, not coherent
with the processor caches. PCI semantic transactions on AGP to system SDRAM are snooped.
AGP semantic accesses to the hub interface/PCI are not supported. PCI semantic accesses from an
AGP master to hub interface are also not supported.
Lock Behavior
If the processor has established a lock to AGP, the GMCH immediately retries incoming FRAME#
cycles. The reads will not be processed internally as a delayed transaction.
If the processor has established a lock to another resource other than AGP, the GMCH will accept
incoming FRAME# cycles based on the other retry/disconnect rules. Since snoops cannot be
generated to the processor while a lock is outstanding, eventually the GMCH’s PCI interface backs
up.
Intel^® 82845G/82845GL/82845GV GMCH Datasheet
111