Hub Datasheet

152 Intel
®
E7505 Chipset MCH Datasheet
System Address Map
4.3 SMM Space
4.3.1 System Management Mode (SMM) Memory Range
The E7505 chipset supports the use of main memory as System Management RAM (SMM RAM),
which enables the use of System Management Mode. The MCH supports three SMM options:
• Compatible SMRAM (C_SMRAM)
• High Segment (HSEG)
• 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 operating
system so the processor has immediate access to this memory space upon entry to SMM. The 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 larger write-thru cacheable TSEG area from 128 KB to 1 MB in size above 1 MB that
is reserved below the 4 GB in system DRAM memory space. The above 1 MB solutions
require changes to compatible SMRAM handler code to properly execute above 1 MB.
4.3.2 TSEG SMM Memory Space
The TSEG SMM space (TOLM – TSEG to TOLM) allows system management software to
partition a region of main memory just below the top of low memory (TOLM) that is accessible
only by system management software. This region may be 128 KB, 256 KB, 512 KB, or 1 MB in
size, depending upon the ESMRAMC.TSEG_SZ field. This space must be below 4 GB, so it is
below TOLM and not the top of physical memory, SMM memory is globally enabled by
SMRAM.G_SMRAME. Requests may access SMM system memory when either SMM space is
open (SMRAM.D_OPEN) or the MCH receives an SMM code request on its system bus. To access
the TSEG SMM space, TSEG must be enabled by ESMRAMC.T_EN. When all of these
conditions are met, a system bus access to the TSEG space (between TOLM–TSEG and TOLM) is
sent to system memory. When the high SMRAM is not enabled or if the TSEG is not enabled,
memory requests from all interfaces are forwarded to system memory. When the TSEG SMM
space is enabled, and an agent attempts a non-SMM access to TSEG space, then the transaction is
specially terminated.
Hub interface originated accesses are not allowed to SMM space.