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Thermal Management

Introduction​

Thermal management is the area concerned with making sure that the system and its components operate within defined temperature ranges, to guarantee the reliable operation of the whole system. It involves concepts such as power consumption, heat dissipation, and system temperature, which are related to the following topics:

  • Hardware: the heat generation is directly proportional to the power consumption of the device. Also, each different component has its specific operating temperature ranges and limits. Usually, one is concerned with the System on Chip (SoC) heat dissipation and the (System on Module) SoM operating temperature ranges. The optimal design of the carrier board may help reduce the power consumption of the system, which may reflect on a significant heat reduction.
  • Software: the power consumption - and thus the heat generation - of the system and its components are affected by the software load put on the hardware components, such as CPU cores, GPU, and peripherals. It is directly related to the use-case application but also affected by the BSP version and its fine-tuning.
  • Enclosing: the mechanical enclosing of the system - a box, for instance - must be taken into account when it comes to thermal management. A low-power SoM may fit a constrained enclosing, whereas a high-performance system may require a well-designed airflow or ventilation scheme for proper operation.
  • Environment: heat flux intensity depends on a difference of temperature, which in our case is the difference between the hardware - usually the SoC in this case - and the environment. Knowing the environment temperature range where the system will operate is essential for designing a thermal management solution that both satisfies the system requirements and uses the least complex cooling mechanism possible.

This article provides an overview of thermal management solutions applied to the Toradex system SoMs. It goes through the hardware and software BSP specifics as well as cooling solutions.

Hardware​

This section goes through the hardware specifics related to thermal management.

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Additional information can be found in the respective Toradex SoMs datasheets, under the Thermal Specification section. The datasheets are available in the corresponding product pages, under the Datasheets tab.

SoC (CPU) Limits​

The following table provides the maximum junction temperature for a specific SoC. Notice that this is the maximum temperature at the semiconductor level, measured by a sensor internal to the SoC die. This temperature is higher than the die/case temperature and is monitored by the underlying operating system and/or additional hardware mechanisms. If temperature throttling mechanisms fail to keep the SoC from reaching the junction temperature, a forced system shutdown is issued to prevent permanent damage.

Browse the dropdown table below for information about maximum junction temperature sorted by SoC:

Maximum Junction Temperature by SoC
FamilySoCMax. Junction Operating Temperature (°C)Thermal Resistance Junction-to-Ambient (°C/W)
Apalisi.MX 8QuadMax+12511.7
Apalisi.MX 8QuadMax IT+12511.7
Apalisi.MX 8QuadPlus+12511.7
Colibrii.MX 8QuadXPlus IT+12515.2
Colibrii.MX 8DualX+12515.2
Verdini.MX 8M Mini DualLite+9522.9
Verdini.MX 8M Mini DualLite IT+10522.9
Verdini.MX 8M Mini Quad IT+10522.9
Verdini.MX 8M Plus Quad+9520.44
Verdini.MX 8M Plus Quad IT+10520.44
Verdini.MX 8M Plus QuadLite IT+10520.44
Colibrii.MX7 Dual+10530.2
Colibrii.MX7 Solo+10530.2
Apalisi.MX6 Quad+10522.0
Apalisi.MX6 Quad IT+10515.0
Apalisi.MX6 Dual+10522.0
Apalisi.MX6 Dual IT+10515.0
Colibrii.MX6 DualLite+9523.0
Colibrii.MX6 DualLite IT+10523.0
Colibrii.MX6 Solo+9523.0
Colibrii.MX6 Solo IT+10523.0
Colibrii.MX 6ULL+9536.2
Colibrii.MX 6ULL IT+10536.2
ApalisTegra K1+10512.3
Apalis / ColibriTegra 3+9011.6
Apalis / ColibriTegra 3 IT+10511.6
ColibriTegra 2+9018.7
ColibriTegra 2 IT+10518.7
ColibriVF61 IT+10528.0
ColibriVF50+10528.0
ColibriVF50 IT+10528.0

SoM Limits​

The operating temperature of all the electrical components in an SoM defines the final module specification. As a consequence, the most critical element regarding temperature limits may not be the SoC, but instead another part. The dropdown tables below list the operating temperature range by Toradex SoM:

Apalis Family​

Maximum Operating Temperature by Apalis SoM
ModuleMin. Operating Temperature (°C)Max. Operating Temperature (°C)
Apalis iMX8 QuadMax 4GB Wi-Fi / Bluetooth IT-40+85
Apalis iMX8 QuadMax 4GB IT-40+85
Apalis iMX8 QuadPlus 2GB Wi-Fi / Bluetooth-25+85
Apalis iMX8 QuadPlus 2GB-25+85
Apalis iMX6 Quad 2GB IT-40+85
Apalis iMX6 Quad 1GB0+70
Apalis iMX6 Dual 1GB IT-40+85
Apalis iMX6 Dual 512MB0+70
Apalis TK1 2GB-25+85
Apalis T30 2GB0+70
Apalis T30 1GB0+70
Apalis T30 1GB IT-40+85

Colibri Family​

Maximum Operating Temperature by Colibri SoM
ModuleMin. Operating Temperature (°C)Max. Operating Temperature (°C)
Colibri iMX8 QuadXPlus 2GB Wi-Fi / Bluetooth IT-40+85
Colibri iMX8 QuadXPlus 2GB IT-40+85
Colibri iMX8 DualX 1GB Wi-Fi / Bluetooth-25+85
Colibri iMX8 DualX 1GB-25+85
Colibri iMX7 Dual 1GB-20+85
Colibri iMX7 Dual 512MB-20+85
Colibri iMX7 Solo 256MB-20+85
Colibri iMX6 DualLite 512MB0+70
Colibri iMX6 DualLite 512MB IT-40+85
Colibri iMX6 Solo 256MB0+70
Colibri iMX6 Solo 256MB IT-40+85
Colibri iMX6ULL 512MB Wi-Fi / Bluetooth IT-40+85
Colibri iMX6ULL 512MB Wi-Fi / Bluetooth0+70
Colibri iMX6ULL 512MB IT-40+85
Colibri iMX6ULL 256MB0+70
Colibri T30 1GB0+70
Colibri T30 1GB IT-40+85
Colibri T20 512MB0+70
Colibri T20 512MB IT-40+85
Colibri T20 256MB0+70
Colibri T20 256MB IT-40+85
Colibri VF61 256MB IT-40+85
Colibri VF50 128MB0+70
Colibri VF50 128MB IT-40+85

Verdin Family​

Maximum Operating Temperature by Verdin SoM
ModuleMin. Operating Temperature (°C)Max. Operating Temperature (°C)
Verdin iMX8M Mini Quad 2GB Wi-Fi / Bluetooth IT-40+85
Verdin iMX8M Mini Quad 2GB IT-40+85
Verdin iMX8M Mini DualLite 1GB Wi-Fi / Bluetooth IT-40+85
Verdin iMX8M Mini DualLite 1GB0+70
Verdin iMX8M Plus Quad 4GB Wi-Fi / Bluetooth IT-40+85
Verdin iMX8M Plus Quad 4GB IT-40+85
Verdin iMX8M Plus Quad 2GB Wi-Fi / Bluetooth IT-40+85
Verdin iMX8M Plus Quad 2GB0+70
Verdin iMX8M Plus QuadLite 1GB IT-40+85

Software and BSP​

This section goes through the software and BSP specifics related to thermal management.

Dynamic Voltage and Frequency Scaling (DVFS) and Thermal Throttling​

Dynamic Voltage and Frequency Scaling (DVFS) is a mechanism in which the operating system optimizes power consumption by adjusting the CPU clocks and voltage based on demand. A side-effect of power consumption optimization is that the system generates less heat in workloads that don't make full use of the CPU.

Thermal Throttling is a mechanism implemented in the operating system to preserve the integrity of the processor. It forces reduction of the system clock when it reaches certain temperatures, independent of DVFS.

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DVFS is disabled by default on WinCE. Please see DVFS on Windows Embedded Compact for further information.

CPU Hotplug​

It may be possible to enable/disable CPU cores dynamically if both the SoC and operating system support it, which saves power, thus generating less heat.

General tips​

This section has some tips on how to save power, which may help reduce heat generation and other aspects of the software that may affect thermal management.

  • If using peak performance for a short duration, heat dissipation is not a matter of concern because of the advanced power management.
  • Cooling solutions may optimize system performance.
  • Colling solutions can be passive or active.
  • When the application requires full CPU / Graphics performance for a more extended period, a general recommendation is testing the system's thermal behavior in the given condition.
  • Always refer to the Thermal Specification section in the respective module datasheet.
  • Thermal throttling configuration, also referred to as temperature trip points, can be adjusted in the BSP.
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We recommend the measuring of the system's power consumption, before and after making the changes. It helps in getting a better understanding of the power management of the system.

OS Specific Guidelines​

Choose your OS from the tabs below:

Linux​

Using Linux, DVFS can be disabled, and the CPU frequency manually set. See the CPU Frequency (Linux) article.

An application in the userspace can monitor the temperature. How to read it and which sensors are available is module-dependent. See the Temperature Sensor (Linux) article and Apalis/Colibri T30 Temperature Monitoring for additional information.

The Linux kernel executes the Thermal Throttling, and the generic Thermal Sysfs API provides access to its settings. The section below includes information about how to set temperature trip points in Linux:

How to Set Temperature Trip Points​

There are two temperature trip points used on iMX SoCs.

  • passive: This is the point where Linux starts to throttle the CPU.
  • critical: This is the point where Linux shuts itself down to protect the CPU.

Toradex decided to use the T_junction_max stated in the datasheet for the critical temperature and 10°C less for the passive trip point.

The following patch should be a guideline how to change these trip-points for iMX related SoCs:

i.MX 6(ULL) / i.MX 7​
diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 28072a7..591d6be 100644
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -656,10 +656,10 @@ static int imx_get_sensor_data(struct platform_device *pdev)
     }
 
     /*
-     * Set the critical trip point at 5C under max
+     * Set the critical trip point at max
      * Set the passive trip point at 10C under max (can change via Sysfs)
      */
-    data->temp_critical = data->temp_max + (1000 * 10);
+    data->temp_critical = data->temp_max;
     data->temp_passive = data->temp_max - (1000 * 10);
 
     return 0;

data->temp_max in this driver is used for the T_junction_max that is read out from the fuses.

data->temp_passive and data->temp_critical are the temperatures described above that a developer should set with the desired temperature in milli-degree Celsius.

i.MX 8/8X/8M Mini/8M Plus​

The i.MX 8/8X power management and temperature monitoring are entirely handled by the System Controller Firmware (SCFW).

The critical and passive points threshold set in their dtsi file and specify CONFIG_IMX8M_THERMAL in defconfig.

The thermal driver can be accessed through the following interface:

  • /sys/class/thermal/thermal_zoneX for i.MX 8 and i.MX 8X.
  • /sys/class/thermal/thermal_zone0 for i.MX 8M Mini.
  • /sys/class/thermal/thermal_zoneX for i.MX 8M Plus.

Inside the above directory, there are files named trip_point*. There you can read the type, current temperature, and hysteresis used by those trip points.

If you want to change the trip points, and you are using a i.MX 8M Mini/8M Plus, it'll require a deeper understanding on how they are configured by the system. There are two cases:

  • The temperature trip points for the thermal zones are edited by u-boot considering the SoC that was detected at runtime.
  • The trip points that are set on the kernel device tree are used by the NXP “wait for cooling” feature in u-boot. Whenever u-boot detects that the SoC is too hot, it stops the boot process and waits until the temperature is lower than the thresholds that are defined in the device tree.

Edit the trip points directly on the device tree only affects the cooling feature in u-boot (2nd case), but in this case, they are not persistent between boots. If you need the configuration to be persistent, it is possible to edit the trip points using sysfs, in which a systemd service can be created to perform the edit on boot.

CPU Hotplug​

See the article CPU (Linux) for detailed information on supported modules.

Additional Tips and Recommendations​

  • Disable unused Display Interfaces

  • Use a Lower Frequency

    • See the CPU Frequency (Linux) article to change the CPU frequency to test system performance and power consumption.

  • Avoid Toggling Pins

    • Make sure none of the pins are unnecessarily toggling. Also, make sure all input pins are in a defined state. The GPIO command-line tools will be helpful in testing, and the Device Tree Customization helps on tweaking the SoC pins configuration for device tree enabled modules.

  • Use Low Power Modes

    • Enter Suspend mode during idle time or even consider switching off the module completely. See the Suspend/Resume (Linux) article for reference.

  • Check CPU Load

    • Linux has many tools to monitor CPU load, such as top, htop, etc. If this value is unexpectedly high, then check the application software. Some easy modifications may help to lower the CPU load. e.g., use interrupts instead of polling, sleep instead of busy waits, etc.

  • Disable unused Drivers

    • For this step, you should measure the power consumption; in some cases, disabling drivers may negatively impact on power consumption. For this purpose, you may have to recompile the Linux kernel and modules. See the article Build U-Boot and Linux Kernel from Source Code for reference.

Mechanical Considerations - Cooling Solutions​

Colling solutions usually target the SoC and can be either passive or active. Passive means that the natural convection transports the heat from the surface to the air. By passive definition, it includes both having the SoC exposed to the environment with or without a heatsink. The efficiency of natural convection is dependent on the housings and the environment. This solution has no moving parts and does not produce noise. If the passive cooling is not sufficient, the most common active cooling solution for embedded systems is the use of a DC fan on top of the heat sink, which increases efficiency dramatically.

If a box encloses the hardware, there are two recommended approaches:

  1. The design of the enclosure should optimize the airflow.
  2. The enclosure should thermally couple to the SoC.

The temperature inside the enclosing has to respect the SoM operating temperature range.

Apalis​

The Apalis family has a robust, rigid mounting mechanism to support thermal solutions. It is ready-to-use on Toradex carrier boards and, if you plan to design your carrier board, the thermal solution implementation guidelines are available in the Apalis Carrier Board Design Guide.

The optimized Apalis Heatsink is available for each version of the Toradex Apalis module. The following table shows the compatibility of the available Apalis heatsinks:

Apalis Heatsink TypeCompatible Module
Type 1Apalis iMX6Q IT
Apalis iMX6D IT
Type 2Apalis T30
Type 3Apalis iMX6Q
Apalis iMX6D
Apalis TK1
Type 4Apalis iMX8QM

The Apalis heatsink has four holes intended for mounting a fan on top of it. Specifics are available in the Apalis Heatsink Fan article. Also, a 3D CAD model of the heatsink is available in the 3D CAD models page.

Apalis Heatsink

Colibri​

The Colibri family of SoMs does not have a cooling solution officially provided by Toradex. Nevertheless, we have tested a few off-the-shelf heatsink solutions available in the market with Colibri T20 and T30 modules. For more details, please refer to the following test reports:

Verdin​

The Verdin family has a robust, rigid mounting mechanism to support thermal solutions. It is ready-to-use on Toradex carrier boards and, if you plan to design your carrier board, the thermal solution implementation guidelines are available in the Verdin Carrier Board Design Guide.

The optimized Verdin Industrial Heatsink is available for each version of the Toradex Verdin module. The following table shows the compatibility of the available Verdin Industrial Heatsink:

Verdin Heatsink TypeCompatible Module
Type 1Verdin iMX8M Mini
Verdin iMX8M Plus

Verdin Industrial Heatsink

Legacy Information​

Colibri PXAxxx​

Colibri PXAxx modules run at a fixed frequency. Toradex provides ways to manually change the system frequency to tweak or optimize the system performance using software configurations. In most of the use cases, a cooling solution is not necessary. The maximum temperature is the case temperature of the PXA processor, which must not exceed 85°C. For more details, please refer to the respective Colibri module datasheet and Marvell's EMTS.



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