AGP Bus Issues

AGP Configuration Space Requirements

Some legacy operating systems require that the AGP capability registers be mapped at Bus 0, Device 0, and Function 0. Also, The AGP aperture base address configuration register must be at Bus 0, Device 0, Function 0, Offset 10h. In a legacy system, these registers are located within the Host to PCI bridge configuration space (Host to HT bridge in our example). See Figure 20-5.

Figure 20-5. Legacy Configuration Mapping for Host to HT Bridge with AGP and DRAM Controller

For complete legacy software support, the specification recommends that the AGP subsystem be designed as follows:

  • AGP bridges are ...

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