Difference between revisions of "ACPI"

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C States can be configured in ACPI using two methods:
C States can be configured in ACPI using two methods:
1. by defining the P_BLK base address in the Processor() Definition, and P_LVLx_LAT values in the FADT
# by defining the P_BLK base address in the Processor() Definition, and P_LVLx_LAT values in the FADT
2. using the _CST Object
# using the _CST Object


P_BLK is easier to configure, if the hardware supports that method. ACPI defines that there must be two registers at P_BLK+4 and P_BLK+5 that initiate a transition to C2 or C3 when the register is read. After sleep, the read returns 0. P_LVLx_LAT define the worst case latency of the state transition.
P_BLK is easier to configure, if the hardware supports that method. ACPI defines that there must be two registers at P_BLK+4 and P_BLK+5 that initiate a transition to C2 or C3 when the register is read. After sleep, the read returns 0. P_LVLx_LAT define the worst case latency of the state transition.
_CST is necessary if you want to support more than 3 C states, or if the transition procedure doesn't follow the ACPI requirement


==== PCI root bus _CRS method ====
==== PCI root bus _CRS method ====

Revision as of 14:53, 16 March 2009