Processor Configuration Registers
60
Datasheet, Volume 2
2.5.14
PCIEXBAR—PCI Express Register Range Base Address
Register
This is the base address for the PCI Express configuration space. This window of
addresses contains the 4 KB of configuration space for each PCI Express device that
can potentially be part of the PCI Express Hierarchy associated with the Uncore. There
is no actual physical memory within this window of up to 256 MB that can be
addressed. The actual size of this range is determined by a field in this register.
Each PCI Express Hierarchy requires a PCI Express Base register. The Uncore supports
one PCI Express Hierarchy. The region reserved by this register does not alias to any
PCI2.3 compliant memory mapped space. For example, the range reserved for
MCHBAR is outside of PCIEXBAR space.
On reset, this register is disabled and must be enabled by writing a 1 to the enable field
in this register. This base address shall be assigned on a boundary consistent with the
number of buses (defined by the length field in this register), above TOLUD and still
within 39-bit addressable memory space.
The PCI Express Base Address cannot be less than the maximum address written to the
Top of physical memory register (TOLUD). Software must ensure that these ranges do
not overlap with known ranges located above TOLUD.
Software must ensure that the sum of the length of the enhanced configuration region
+ TOLUD + any other known ranges reserved above TOLUD is not greater than the 39-
bit addressable limit of 512 GB. In general, system implementation and the number of
PCI/PCI Express/PCI-X buses supported in the hierarchy will dictate the length of the
region.
All the bits in this register are locked in Intel TXT mode.
