Switch User Manual

Intel

82854 Graphics Memory Controller Hub (GMCH)

116 D15343-003

5.4.2.1 Extended SMRAM Address Range (HSEG and TSEG)

The HSEG and TSEG SMM transaction address spaces reside in this extended system memory

area.

5.4.2.2 HSEG

SMM mode CPU accesses to enabled HSEG are remapped to 000A0000h-000BFFFFh. Non-SMM

mode CPU accesses to enabled HSEG are considered invalid are terminated immediately on the

FSB. The exceptions to this rule are Non-SMM mode Write Back cycles that are remapped to

SMM space to maintain cache coherency. Hub interface originated cycles to enabled SMM space

are not allowed. Physical DDR SDRAM behind the HSEG transaction address is not remapped and

is not accessible.

5.4.2.3 TSEG

TSEG is 1-MB in size and is at the top of physical system memory. SMM mode CPU accesses to

enabled TSEG access the physical DDR SDRAM at the same address. Non-SMM mode CPU

accesses to enabled TSEG are considered invalid and are terminated immediately on the FSB. The

exceptions to this rule are Non-SMM-mode Write Back cycles that are directed to the physical

SMM space to maintain cache coherency. Hub interface originated cycles that enable SMM space

are not allowed.

The size of the SMRAM space is determined by the USMM value in the SMRAM register. When

the extended SMRAM space is enabled, non-SMM CPU accesses and all other accesses in this

range are forwarded to the Hub interface. When SMM is enabled the amount of system memory

available to the system is equal to the amount of physical DDR SDRAM minus the value in the

TSEG register.

5.4.2.4 Dynamic Video Memory Technology (DVMT)

The IGD supports DVMT in a non-graphics system memory configuration. DVMT is a mechanism

that manages system memory and the internal graphics device for optimal graphics performance.

DVMT-enabled software drivers, working with the memory arbiter and the operating system,

utilize the system memory to support 2D graphics and 3D applications. DVMT dynamically

responds to application requirements by allocating the proper amount of display and texturing

memory.