Intel B940 Datasheet Page 239

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Datasheet, Volume 2 239
Processor Configuration Registers
2.16.15 PLMBASE_REG—Protected Low-Memory Base Register
This register is used to set up the base address of DMA-protected low-memory region
below 4 GB. This register must be set up before enabling protected memory through
PMEN_REG, and must not be updated when protected memory regions are enabled.
This register is treated as RO for implementations not supporting protected low
memory region (PLMR field reported as Clear in the Capability register).
The alignment of the protected low memory region base depends on the number of
reserved bits (N:0) of this register. Software may determine N by writing all 1s to this
register, and finding the most significant bit position with 0 in the value read back from
the register. Bits N:0 of this register are decoded by hardware as all 0s.
Software must setup the protected low memory region below 4 GB. The VTd
specification describes the Protected Low-Memory Limit register and hardware
decoding of these registers.
Software must not modify this register when protected memory regions are enabled.
(PRS field Set in PMEN_REG).
B/D/F/Type: 0/0/0/DMIVC1REMAP
Address Offset: 68–6Bh
Reset Value: 00000000h
Access: RW, RO
Bit Attr
Reset
Value
Description
31:21 RW 000h
Protected Low-Memory Base (PLMB)
This register specifies the base of protected low-memory region in system
memory.
20:0 RO 000000h Reserved
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