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The Dragonwing IQ‑9075 EVK is designed to consume up to 70 W, necessitating a substantial thermal solution. The default cooling solution is fan‑based, using a CPU cooler mounted to the bottom of the device. The fan controller used on this board is a Texas Instruments AMC6821SQDBQRQ1 PWM fan controller IC. The fan is connected using the JFAN connector (S6B‑XH‑SM4‑TB(LF)(SN)) on the mainboard. Fan Connector details with IQ-9075 EVK main board:

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Overview

The fan controller regulates fan speed based on temperature inputs to ensure optimal thermal performance and energy efficiency. It supports multiple operating modes and can be configured dynamically through system nodes.

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Features

  • Supports two operating modes: Manual and Automatic (Mode 2)
  • Dynamic fan speed control based on temperature inputs

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Operating Modes

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How It Works

1

Initialization

System boots and loads fan controller configuration.
2

Mode Selection

The pwm1_enable node is set to 2 for automatic mode.
3

Temperature Monitoring

Remote temperature sensors continuously monitor system temperature.
4

PWM Adjustment

Based on temperature, the controller adjusts the PWM signal (0–255) to control fan speed.
5

Fan Speed Control

Fan speed (fan1_input) increases or decreases accordingly.
6

Threshold Handling

If temperature drops below temp2_auto_point1_temp, the fan is turned off.

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Mode Details and Validation

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Description

In Auto Mode, fan speed is automatically controlled based on the remote temperature sensor (temp2_input). The system adjusts fan power and speed according to predefined temperature thresholds to ensure efficient cooling.

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Node Path

All relevant nodes are located under:

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Temperature Thresholds

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Key Nodes

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Validation

For IQ-9075, amc6821 is located at hwmon0, so X = 0.
1

Confirm Mode

Ensure the output is 2.
2

Monitor Temperature

3

Check Fan Speed

4

Check Power Input

5

Observe Behavior

  • Below temp2_auto_point1_temp: Fan should stop (fan1_input = 0, pwm1 = 0)
  • Between point1 and point2: Fan runs slowly (pwm1 ≈ 85)
  • Between point2 and point3: Fan runs at full speed (pwm1 = 255)
The actual hwmon number for the AMC6821 fan controller may vary. To determine the correct number:
Expected output: