LM93 datasheet(16/95 Pages) TI1

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LM93

SNAS210E – DECEMBER 2003 – REVISED MARCH 2013

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3.9

PROCHOT BACKGROUND INFORMATION

PROCHOT is an output from a processor that indicates that the processor has reached a predetermined

temperature trip point. At this trip point the processor can be programmed to lower its internal operating

frequency and/or lower its supply voltage by changing the value of the 6 bit VID that it supplies to the

VRD. The final VID setting and the rate at which it transitions to the new VID is programmable within the

processor.

If PROCHOT is 100% throttled, it does not mean that the CPU is not executing, but it may mean that the

CPU is about to encounter a thermal trip if the processor temperature continues to rise.

PROCHOT is also an input to some processors so that an external controller can force a thermal throttle

based on external events.

PROCHOT is no longer asserted by the processor when the temperature drops below the predefined

thermal trip point.

Oscillation around the trip point is avoided by the processor by requiring that the temperature be

above/below the trip point for a predetermined period of time. A counter inside the processor is used to

track this time and it has to be incremented to a max count for an above temperature trip and

decremented to zero when below the trip temperature setting, to remove the trip.

The minimum time for PROCHOT assertion is time dependant on the FSB frequency. The minimum time

that the processor asserts PROCHOT is estimated to be 187 µs.

3.10 PROCHOT MONITORING

PROCHOT monitoring applies to both the P1_PROCHOT and P2_PROCHOT inputs. Both inputs are

monitored in the same fashion, but the following description discusses a single monitor. (Px_PROCHOT

represents both P1_PROCHOT and P2_PROCHOT).

PROCHOT monitoring is meant to achieve two goals. One goal is to measure the percentage of time that

PROCHOT is asserted over a programmable time period. The result of this measurement can be read

from an 8-bit register where one LSB equals 1/256th of the PROCHOT Time Interval (0.39%). The second

goal is to have a status register that indicates, as a coarse percentage, the amount of time a processor

has been throttled. This second goal is required in order to communicate information over the NIC using

ASF, i.e. status can be sent, not values.

To achieve the first goal, the PROCHOT input is monitored over a period of time as defined by the

PROCHOT Time Interval Register. At the end of each time period, the 8-bit measurement is transferred to

the Current Px_PROCHOT register. Also at the end of each measurement period, the Current

Px_PROCHOT register value is moved to the Average Px_PROCHOT register by adding the new value to

the old value and dividing the result by 2. Note that the value that is averaged into the Average

Px_PROCHOT register is not the new measurement but rather the previous measurement. If the SMBus

writes to the Current P1_PROCHOT (or Current P2_PROCHOT) register, the capture cycle restarts for

both monitoring channels (P1_PROCHOT and P2_PROCHOT). Also note, that a strict average of two 8-

bit values may result in Average Px_PROCHOT reflecting a value that is one LSB lower than the Current

Px_PROCHOT in steady state.

It should be noted that the 8-bit result has a positive bias of one half of an LSB. This is necessary

because a value of 00h represents that Px_PROCHOT was not asserted at all during the sampling

window. Any amount of throttling results in a reading of 01h.

The following table demonstrates the mapping for the 8-bit result:

SPACER

Functional Description

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