intel® joule™ developer kit & innovator group overview intent of thermal management the...

Thermal Management Overview

Revision 1.0

November 2016

Intel® Joule™ Developer Kit

Maker & Innovator Group

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Contents:1. Thermal Management Objectives

2. Hardware Control and Firmware Settings

3. Workload Measurement and Setting Power Limit in BIOS

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Thermal Management Objectives

Section 1


OverviewIntent of thermal management

The Intel® Joule™ compute module integrates a powerful four-core, 64-bit Intel® Atom™ processor, high definition graphics, and wireless communications into a compact system on module (SoM) form factor.

The module generates thermal energy relative to workload; the goal of thermal management is to maintain balance between user safety, system performance, and platform capacity for heat dissipation.

Successful thermal management techniques:

• Provide user safety through thermal ergonomics that control exposed surface temperatures.

• Prevent thermal runaway (uncontrolled overheating) that can result in platform instability.

Thermal management solutions will vary significantly per use case:

• Device workloads and software decisions can have the greatest influence on thermal generation.

• Operating environments and enclosure designs are a critical part of thermal calculations.

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OverviewThermal management basics

The module provides two (BIOS) methods that work together to maintain a thermal target. It is the responsibility of the developer and validation team to ensure each is properly configured and enabled.

Temperature Limit Setting:

• Programmable temperature when throttling to begins; module shutdown will happen at 105˚C.

• Can be set lower than the programmed maximum of (75˚C) to accommodate for safety ergonomics.

Run-time Average Power Limit (RAPL):

• Module firmware can automatically adjust processor power to maintain temperature targets.

• The fixed maximum power limit helps avoids issues that can arise from rapid thermal transients.

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OverviewThermal control methods

There and numerous ways to remove thermal energy (heat) from the module. This overview outlines the reference heatsink and cooling fan assembly mounted to the Intel® Joule™ module expansion board.

Passive dissipation:

• Workloads with low heat generation can radiate thermal energy into their environment.

• Enclosures can be designed to encourage thermal convection (natural airflow).

Active control:

• A powered fan can provide constant airflow across the thermal plate or heatsink.

• Module power can be varied to maintain module within an ideal thermal range.

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Hardware Control and Firmware Settings

Section 2


Hardware ControlIntroduction

The module provides hardware thermal controls that are intended to maintain operation within a set temperature range by adjusting processor speed or capping the maximum power consumption.

These controls are configured within the BIOS; they operate independently of any operating system or software based thermal control loops and can influence system performance and power consumption.

• Thermal Control Circuit (TCC): Specified maximum temperature limit at which processor power will be automatically reduced. TCC can be set below the maximum default value, but not above it. The amount and rate of processor speed adjustment is hardcoded in the module and cannot be changed.

• Power Limit 1 (PL1): Processor Run-time Averaged Power Limit (RAPL). PL1 is a static limit of the maximum module power while TCC is below set point. When module temperature is above the TCC set point, the TCC function dynamically lowers PL1 until the TCC value returns below the set point.

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Hardware ControlEnter the module BIOS system

Press the [F2] key during boot up splash to enter the BIOS system.

Select “Device Manager” using arrow keys depress the [ENTER] key to reach the next menu level.

Select “System Setup” and depress the [ENTER] key to reach the next menu level.

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Hardware ControlSelect CPU Configuration menu and enable the TM1 and DTS sensors

Next select the CPU Power Management sub-menu.

The TM1 and DTS (module thermal sensors) must be enabled for the TCC to function.

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Power Limit 1 attributes:

Hardware ControlSet PL1 attributes as needed for design intent, environment, and workload

Use the Go Back option to navigate and [F4] to commit changes.

Power Limit 1 Function [Enable / Disable]Disable will allow module to operate without input power limit and prevents software thermal controls that utilize the PL1 function.

Power Limit 1 Power [#]Range from 1 to 10 in whole numbers

4 is recommended max with reference heatsink and no fan.

5 and above should have active cooling solutions.

8 is only recommended for fully profiled and validated designs.

Power Limit 1 Time Window <#>Smaller time window values increase power sampling and response rate.

Some applications will need a higher value if they have infrequent bursts of workload that are best if not quickly power limited.

Power Limit 1 Clamp Mode [Enable / Disable]Disable will prevent setting clock below base frequency for any domain.

Enable allows firmware to set clock below base to meet thermal target.

It is recommended that Clamp Mode always be enabled.

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Hardware ControlOverview of the Thermal Configuration Parameters

Hardware Control Parameters:

Thermal Control Offset [#]Offset is specified relative to 88 °C (Tj value).

For example, Thermal Control Offset of 10 will result in TCC activation at (Tj) 88 °C – 10 °C offset = 78 °C TCC trip.

Critical Trip Point <### C>Temperature where module will perform an automatic (hard) shutdown without alerting the operating system.

Passive Trip Point <### C>Temperature where the module will assert the TBD signal to inform operating system or other control structure that thermal management needs to activated before the module initiates a hard shutdown.

Automatic Thermal Reporting [Enable / Disable]Enable will permit the BIOS to report ACPI trip points and active cooling gag to ACPI enabled operating systems.

NOTE: The critical and passive trip points are for software packages that support ACPI functions:

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Workload Measurement and Setting Power Limit in BIOS

Section 3


Module Power CharacterizationIntroduction to method

The following elements will facilitate collecting power data that can be used to determine the cooling capacity required to maintain temperatures within a target range for the application workload:

• Active heatsink properly attached to the module.

• BIOS settings configured for maximum system performance.

• Stable and robust platform power supply that exceeds workload needs.

• All accessory devices connected and operational for the defined used case.

The following slides will outline how to configure the platform, and collect the power measurement data that is used to determine the best BIOS power limit settling for the profiled application.

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Module Power CharacterizationConfigure BIOS to allow maximum module performance

• In the CPU settings / System Power Options menu:• Enable Intel® Turbo Boost Technology• Configure Power Limit options as shown:

• In the Thermal menu:• Set Thermal Control Offset to [0]• Disable Automatic Thermal Reporting• Set Critical and Passive trip points to <103 C>

Use the Go Back option and depress [F4] to commit changes to BIOS

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Module Power CharacterizationTheory of measuring processor power

Processor power will be measured by accessing the RAPL driver’s energy counter and recording periodic results to a log file for later analysis. The energy counter counts the amount of energy spent by the processor in micro (1×10-6) joules. Therefore, processor power can be calculated by logging two instances of the energy counter and then dividing the difference by the measurement interval.

𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 =𝐸𝐸𝐸𝐸𝑃𝑃𝑃𝑃𝐸𝐸𝐸𝐸𝑇𝑇𝑇 − 𝐸𝐸𝐸𝐸𝑃𝑃𝑃𝑃𝐸𝐸𝐸𝐸𝑇𝑇𝑇

𝑇𝑇𝑇 − 𝑇𝑇𝑇

RAPL driver’s energy counter can be accessed at /sys/class/powercap/intel-rapl/intel-rapl:0/energy_ujand an example script to collect data is shown on the following page.

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Module Power CharacterizationUsing a shell script to capture power data

2. Power measurement script example to collect power, in watts, every two seconds (adjust as appropriate).while truedo

P1=$(cat /sys/class/powercap/intel-rapl/intel-rapl\:0/energy_uj)T1=$(date +%s)sleep 2P2=$(cat /sys/class/powercap/intel-rapl/intel-rapl\:0/energy_uj)T2=$(date +%s)PWR=$(echo “scale=2;($P2-$P1)/($T2-$T1)/1000000” | bc)echo $PWR

done

3. Run your application and the power measurement script simultaneously to collect workload data.

1. Stop executing Thermal Daemon to halt operating system based thermal controls.sh-4.3# ps~~~~~~~~~~~~~~~~580 root 50543 S /usr/sbin/connmand –n586 root 123m S /usr/sbin/thermald --no-daemon --dbus-enable --config-file590 root 21456 S STUBINIT601 root 43289 S /usr/sbin/wpa_supplicant –u~~~~~~~~~~~~~~~~sh-4.3# kill 586

Note: This script measures time averaged power, which is useful for thermal assessment.

This method will not measure instantaneous spikes that are needed for power delivery validation.

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Module Power CharacterizationReading the log to determine peak power consumption

After running the target application through all use cases and long enough to collect sufficient data, stop the logging script activity and open the log file. The long file contains Watts used expressed as integers.

Module power limit (PL1) should be set at the next whole number above maximum power recorded.

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log data:….51.691.101.402.302.502.502.101.30.75.44…

The log files shows a peak power consumption of 2.50 Watts.

PL1 is set in whole number increments, setting PL1 to 3 provides reasonable

overhead capacity and device protection.


This chart shows the ambient temperature (Y-axis) range for a known workload (X-axis) when using either the passive reference heatsink or the reference heatsink combined with a forced air fan.

Our example 2.5 Watt application can run with the reference heatsink, as long as the ambient temperature remains below 30 ˚C and above 30 ˚C with the addition of a fan.

With the reference heatsink and a forced air fan, a 7 Watt application could run in an ambient environment of up to 25 ˚C.

Results will vary per fan size, speed and placement location upon the platform.

2.5 Watt Application

Heatsink Selection for Example Application

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Reference heatsink

without a fan

Reference heatsink with

a fan

7 Watt Example

Maker & Innovator GroupUse the Go Back option and depress [F4] to commit changes to BIOS.

Module Power CharacterizationConfigure BIOS settings for characterized results

• In the CPU settings / System Power Options menu:• Choose Intel® Turbo Boost setting for your use case.• Set PL1 to next whole number above the max power recorded in the log file; 3 for our 2.5W example.

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