Intel 815 - Manual (Page 80)

AGP/Display Cache Design Guidelines
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80 Intel
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815 Chipset Platform Design Guide
7.1.1 Graphics Performance Accelerator (GPA)
The GMCH multiplexes the AGP signal interface with the integrated graphics’ display cache
interface. As a result, for a universal motherboard that supports both integrated graphics and add-
in AGP video cards, display cache (for integrated graphics) must be populated on a card in the
universal AGP slot. The card is called a Graphics Performance Accelerator (GPA) card. Intel
provides a specification for this card in a separate document (Graphics Performance Accelerator
Specification).
AGP guidelines are presented in this section for motherboards that support the population of a
GPA card in their AGP slot, as well as for those that do not. Where there are distinct guidelines
dependent on whether or not a motherboard will support a GPA card, the section detailing routing
guidelines is divided into subsections, as follows:
•
If the motherboard supports a GPA card populated in the AGP slot, then the guidelines in the
Flexible Motherboard subsections are to be followed.
•
If the motherboard will NOT support a GPA card populated in the AGP slot, then the
guidelines in the AGP-Only Motherboard subsections are to be followed.
7.1.2 AGP Universal Retention Mechanism (RM)
Environmental testing and field reports indicate that AGP cards and Graphics Performance
Accelerator (GPA) cards may come unseated during system shipping and handling without proper
retention. To avoid disengaged AGP cards and GPA modules, Intel recommends that AGP-based
platforms use the AGP retention mechanism (RM).
The AGP RM is a mounting bracket that is used to properly locate the card with respect to the
chassis and to assist with card retention. The AGP RM is available in two different handle
orientations: left-handed (see Figure 42) and right-handed. Most system boards accommodate the
left-handed AGP RM. The manufacturing capacity of the left-handed RM currently exceeds the
right-handed capacity, and as a result Intel recommends that customers design their systems to
insure they can use the left-handed version of the AGP RM (see Figure 42). The right-handed
AGP RM is identical to the left-handed AGP RM, except for the position of the actuation handle.
This handle is located on the same end as the primary design, but extends from the opposite side
(mirrored about the center axis running parallel to the length of the part). Figure 43 contains
keepout information for the left hand AGP retention mechanism. Use this information to ensure the
motherboard design leaves adequate space to install the retention mechanism.
The AGP interconnect design requires that the AGP card must be retained to the extent that the
card not back out more than 0.99 mm (0.039 in) within the AGP connector. To accomplish this it
is recommended that new cards implement an additional notch feature in the mechanical keying
tab to allow an anchor point on the AGP card for interfacing with an AGP RM. The retention
mechanism’s round peg engages with the AGP or GPA card’s retention tab and prevents the card
from disengaging during dynamic loading. The additional notch feature in the mechanical keying
tab is required for 1.5V AGP cards and is recommended for the new 3.3V AGP cards.