Hub Datasheet

154 Intel
®
E7505 Chipset MCH Datasheet
System Address Map
4.4 Memory Re-claim Background
The following memory-mapped I/O devices are typically located below 4 GB:
• High BIOS
• HSEG
• XAPIC
• Local APIC
• System Bus Interrupts
• HI_B BAR
In previous generation MCHs, the physical main memory overlapped by the logical address space
allocated to these memory-mapped I/O devices was unusable. In workstation systems the memory
allocated to memory-mapped I/O devices could easily exceed 1 GB. The result is that a large
amount of physical memory would not be usable.
The MCH provides the capability to re-claim the physical memory overlapped by the memory
mapped I/O logical address space. The MCH re-maps physical memory from the Top of Low
Memory (TOLM) boundary up to the 4 GB boundary (or DRB7 if less than 4 GB) to an equivalent
sized logical address range located just above the top of physical memory
4.4.1 Memory Re-mapping
An incoming address (referred to as a logical address) is checked to see if it falls in the memory re-
map window. The bottom of the re-map window is defined by the value in the REMAPBASE
Register. The top of the re-map window is defined by the value in the REMAPLIMIT Register. An
address that falls within this window is remapped to the physical memory starting at the address
defined by the TOLM Register.