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Intel® Xeon® Processor E5-1600/E5-2600/E5-4600 Product Families 51
Datasheet Volume One
2.5.2.6.14 Package Power SKU Read
This read allows the PECI host to access the minimum, Thermal Design Power and
maximum power settings for the processor package SKU. It also returns the maximum
time interval or window over which the power can be sustained. If the power limiting
entity specifies a power limit value outside of the range specified through these
settings, power regulation cannot be guaranteed. Since this data is 64 bits wide, PECI
facilitates access to this register by allowing two requests to read the lower 32 bits and
upper 32 bits separately as shown in Table 2-8. Power units for this read are
determined as per the Package Power SKU Unit settings described in
Section 2.5.2.6.13.
‘Package Power SKU data’ is programmed by the PCU firmware during boot time based
on SKU dependent power-on default values set during manufacturing. The TDP
package power specified through bits [14:0] in Figure 2-28 is the maximum value of
the ‘Power Limit1’ field in Section 2.5.2.6.26 while the maximum package power in bits
[46:32] is the maximum value of the ‘Power Limit2’ field.
The minimum package power in bits [30:16] is applicable to both the ‘Power Limit1’ &
‘Power Limit2’ fields and corresponds to a mode when all the cores are operational and
in their lowest frequency mode. Attempts to program the power limit below the
minimum power value may not be effective since BIOS/OS, and not the PCU, controls
disabling of cores and core activity.
The ‘maximum time window’ in bits [54:48] is representative of the maximum rate at
which the power control unit (PCU) can sample the package energy consumption and
reactively take the necessary measures to meet the imposed power limits.
Programming too large a time window runs the risk of the PCU not being able to
monitor and take timely action on package energy excursions. On the other hand,
programming too small a time window may not give the PCU enough time to sample
energy information and enforce the limit. The minimum value of the ‘time window’ can
be obtained by reading bits [21:15] of the PWR_LIMIT_MISC_INFO CSR using the PECI
RdPCIConfigLocal() command.
Table 2-9. Power Control Register Unit Calculations
Unit Field Value Calculation Default Value
Time 1s / 2
TIME UNIT
1s / 2
10
= 976 µs
Energy 1J / 2
ENERGY UNIT
1J / 2
16
= 15.3 µJ
Power 1W / 2
POWER UNIT
1W / 2
3
= 1/8 W