Datasheet 227
Host-Secondary PCI Express* Bridge Registers (D6:F0)
8.20 PMLIMITU1—Prefetchable Memory Limit Address
Upper
B/D/F/Type: 0/6/0/PCI
Address Offset: 2C–2Fh
Default Value: 00000000h
Access: RW
Size: 32 bits
The functionality associated with this register is present in the PCI Express design
implementation.
This register in conjunction with the corresponding Upper Limit Address register
controls the processor to PCI Express prefetchable memory access routing based on
the following formula:
PREFETCHABLE_MEMORY_BASE ≤ address ≤ PREFETCHABLE_MEMORY_LIMIT
The upper 12 bits of this register are read/write and correspond to address bits
A[31:20] of the 40- bit address. The lower 8 bits of the Upper Limit Address register
are read/write and correspond to address bits A[39:32] of the 40-bit address. This
register must be initialized by the configuration software. For the purpose of address
decode, address bits A[19:0] are assumed to be FFFFFh. Thus, the top of the defined
memory address range will be at the top of a 1MB aligned memory block.
Note that prefetchable memory range is supported to allow segregation by the
configuration software between the memory ranges that must be defined as UC and the
ones that can be designated as a USWC (i.e., prefetchable) from the processor
perspective.
Bit Access
Default
Value
Description
31:0 RW
0000000
0h
Prefetchable Memory Address Limit (MLIMITU): This field corresponds to
A[63:32] of the upper limit of the prefetchable Memory range that will be passed
to PCI Express.
