Vol. 3C 35-251

MODEL-SPECIFIC REGISTERS (MSRS)

65CH

1628

MSR_PLATFORM_POWER_L

IMIT

Platform*

Platform Power Limit Control (R/W-L) 
Allows platform BIOS to limit power consumption of the platform 

devices to the specified values. The Long Duration power 

consumption is specified via Platform_Power_Limit_1 and 

Platform_Power_Limit_1_Time. The Short Duration power 

consumption limit is specified via the Platform_Power_Limit_2 with 

duration chosen by the processor. 
The processor implements an exponential-weighted algorithm in 

the placement of the time windows.

14:0

Platform Power Limit #1. 
Average Power limit value which the platform must not exceed 

over a time window as specified by Power_Limit_1_TIME field. 
The default value is the Thermal Design Power (TDP) and varies 

with product skus. The unit is specified in MSR_RAPLPOWER_UNIT.

15

Enable Platform Power Limit #1. 
When set, enables the processor to apply control policy such that 

the platform power does not exceed Platform Power limit #1 over 

the time window specified by Power Limit #1 Time Window.

16

Platform Clamping Limitation #1. 
When set, allows the processor to go below the OS requested P 

states in order to maintain the power below specified Platform 

Power Limit #1 value. 
This bit is writeable only when CPUID (EAX=6):EAX[4] is set.

23:17

Time Window for Platform Power Limit #1. 
Specifies the duration of the time window over which Platform 

Power Limit 1 value should be maintained for sustained long 

duration. This field is made up of two numbers from the following 

equation:
Time Window = (float) ((1+(X/4))*(2^Y)), where:
X = POWER_LIMIT_1_TIME[23:22]
Y = POWER_LIMIT_1_TIME[21:17].
The maximum allowed value in this field is defined in 

MSR_PKG_POWER_INFO[PKG_MAX_WIN].
The default value is 0DH, The unit is specified in 

MSR_RAPLPOWER_UNIT[Time Unit].

31:24

Reserved

46:32

Platform Power Limit #2. 
Average Power limit value which the platform must not exceed 

over the Short Duration time window chosen by the processor. 
The recommended default value is 1.25 times the Long Duration 

Power Limit (i.e. Platform Power Limit # 1)

47

Enable Platform Power Limit #2. 
When set, enables the processor to apply control policy such that 

the platform power does not exceed Platform Power limit #2 over 

the Short Duration time window.

Table 35-37.  Additional MSRs Supported by 6th Generation Intel® Core™ Processors Based on Skylake 

Microarchitecture

Register 

Address

Register Name

Scope

Bit Description

 Hex

Dec