Intel B940 Datasheet Page 266

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Processor Configuration Registers
266 Datasheet, Volume 2
2.18.6 RTADDR_REG—Root-Entry Table Address Register
This register provides the base address of root-entry table.
2.18.7 CCMD_REG—Context Command Register
This register manages context cache. The act of writing the uppermost byte of the
CCMD_REG with the ICC field set causes the hardware to perform the context-cache
invalidation.
B/D/F/Type: 0/2/0/GFXVTBAR
Address Offset: 20–27h
Reset Value: 0000000000000000h
Access: RO, RW
Bit Attr
Reset
Value
Description
63:36 RO 0000000h Reserved
35:12 RW 000000h
Root table address (RTA)
This register points to base of page aligned, 4 KB-sized root-entry table in
system memory. Hardware may ignore and not implement bits 63:HAW,
where HAW is the host address width.
Software specifies the base address of the root-entry table through this
register, and programs it in hardware through the SRTP field in the Global
Command register.
Reads of this register return the value that was last programmed to it.
11:0 RO 000h Reserved
B/D/F/Type: 0/2/0/GFXVTBAR
Address Offset: 28–2Fh
Reset Value: 0800000000000000h
Access: RW, RO
Bit Attr
Reset
Value
Description
63 RW 0b
Invalidate Context Cache (ICC)
Software requests invalidation of context-cache by setting this field. Software
must also set the requested invalidation granularity by programming the
CIRG field. Software must read back and check the ICC field is Clear to
confirm the invalidation is complete. Software must not update this register
when this field is Set.
Hardware clears the ICC field to indicate the invalidation request is
complete.Hardware also indicates the granularity at which the invalidation
operation was performed through the CAIG field.
Software must submit a context-cache invalidation request through this field
only when there are no invalidation requests pending at this remapping
hardware unit. Refer to the VTd specification for software programming
requirements.
Since information from the context-cache may be used by hardware to tag
IOTLB entries, software must perform domain-selective (or global)
invalidation of IOTLB after the context cache invalidation has completed.
Hardware implementations reporting a write-buffer flushing requirement
(RWBF=1 in the Capability register) must implicitly perform a write buffer
flush before invalidating the context-cache. Refer to the VTd specification for
write buffer flushing requirements.
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