Intel® 945G/945GZ/945GC/ 945P/945PL Express Chipset Family ...

System Address Map
9.3.8 Graphics Memory Address Ranges (Intel ®
82945G/82945GC/82945GZ GMCH Only)
The GMCH can be programmed to direct memory accesses to IGD when addresses are within any
of three ranges specified via registers in the GMCH’s Device 2 configuration space.
� The Memory Map Base register (MMADR) is used to access graphics control registers.
� The Graphics Memory Aperture Base register (GMADR) is used to access graphics memory
allocated via the graphics translation table.
� The Graphics Translation Table Base register (GTTADR) is used to access the translation
table.
Normally, these ranges will reside above the Top-of-Main-DRAM and below High BIOS and
APIC address ranges. They normally reside above the top of memory (TOLUD) so they do not
steal any physical DRAM memory space.
GMADR is a prefetchable range to apply USWC attribute (from the processor point of view) to
that range. The USWC attribute is used by the processor for write combining.
9.4 System Management Mode (SMM)
System Management Mode uses main memory for System Management RAM (SMM RAM). The
(G)MCH supports Compatible SMRAM (C_SMRAM), High Segment (HSEG), and Top of
Memory Segment (TSEG). System Management RAM space provides a memory area that is
available for the SMI handlers and code and data storage. This memory resource is normally
hidden from the system OS so that the processor has immediate access to this memory space upon
entry to SMM. The (G)MCH provides three SMRAM options:
� Below 1-MB option that supports compatible SMI handlers.
� Above 1-MB option that allows new SMI handlers to execute with write-back cacheable
SMRAM.
� Optional TSEG area of 1 MB, 2 MB, or 8 MB in size. The TSEG area lies below IGD stolen
memory.
The above 1-MB solutions require changes to compatible SMRAM handlers’ code to properly
execute above 1 MB.
Note: DMI and PCI Express masters are not allowed to access the SMM space.
216 Intel ® 82945G/82945GZ/82945GC GMCH and 82945P/82945PL MCH Datasheet