HDMI

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This document describes the connection, identification, display settings, touch usage, and audio/video playback methods for the HDMI display interface under Quectel Pi M2 Debian. An external HDMI display screen is used as an example.

Overview

HDMI is a commonly used audio and video output interface, suitable for desktop display, media playback, debugging operations, industrial dashboards, and human-machine interaction terminals. Quectel Pi M2 provides one HDMI 2.0 interface that can connect to an HDMI display to enter the Debian desktop environment.

The display-related interfaces on the Quectel Pi M2 are shown in the following table:

Interface	Description
HDMI	1× HDMI interface, HDMI 2.0. The display mode is negotiated by the system, monitor EDID, and cable together.
Touch	If the HDMI screen supports touch functionality, an additional USB touch cable is usually required.

Hardware Interface

HDMI Screen Connection

Connect the HDMI display to the HDMI interface on the board, and confirm that the display is properly powered and the HDMI cable is securely connected.

HDMI screen connection diagram:

Connection notes:

1. Before connecting the HDMI display, it is recommended to turn off the board power first.

2. Confirm that the HDMI cable is oriented correctly to avoid stress on the connector.

3. Confirm that the monitor has been switched to the corresponding HDMI input source.

4. If using an HDMI screen with touch functionality, the screen’s USB touch cable must also be connected.

Touch Connection

If the HDMI screen supports touch functionality, connect the screen’s USB touch interface to the board’s USB Host port. After the system recognizes the touch device, you can directly click, drag, and perform window operations in the Debian desktop.

HDMI touch connection diagram:

Quick Start

1. Turn off the board power.

2. Connect the HDMI cable to the board and the HDMI display.

3. Power on the HDMI display and select the corresponding HDMI input source.

4. Power on the board.

5. After the system boots, enter the Debian desktop. The system enters the GNOME desktop by default.

6. To confirm system status, run the following commands in the board terminal:

hostname -I
cat /sys/class/drm/card0-HDMI-A-1/status
cat /sys/class/drm/card0-HDMI-A-1/modes

HDMI desktop display:

Feature Usage (GNOME)

The following features are based on the M2 GNOME desktop environment.

Touch Function

After connecting the HDMI screen’s USB touch cable, you can directly use the touch function in the Debian desktop. If the touch is unresponsive, first check whether the USB touch cable is connected to the USB Host port, then re-plug and check whether the system recognizes the input device:

lsusb
cat /proc/bus/input/devices

Video Playback

You can first push a test video to the Videos directory on the board:

adb push /home/q/work/temp/test-1.mp4 /home/q/Videos/m1-mipi-display-test.mp4

Video playback via GUI: In the Debian desktop, you can use the file manager to navigate to the Videos directory and double-click m1-mipi-display-test.mp4 to play it.

Video playback via GStreamer command line: When playing video from the command line, you can use the following command.

💡 It is recommended to run the following playback commands in the board’s graphical desktop terminal. If executed via an ADB root shell, playback may fail due to missing graphical desktop and audio session environment variables.

In the board’s graphical desktop terminal (logged in as the q user), you can directly run:

gst-launch-1.0 playbin uri=file:///home/q/Videos/m1-mipi-display-test.mp4

If executing via an ADB root shell or SSH root login, first switch to the q user, then set the graphical desktop session environment variables in order, and finally run the playback command:

su - q
export DISPLAY=:0
export WAYLAND_DISPLAY=wayland-0
export XDG_RUNTIME_DIR=/run/user/1000
export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
gst-launch-1.0 playbin uri=file:///home/q/Videos/m1-mipi-display-test.mp4

The following is a screenshot of video playback using the GStreamer command line.

In this test, video playback via both the desktop file manager and GStreamer command line was verified, and the HDMI screen displayed video normally.

Audio Playback

You can first push a test audio file to the Music directory on the board:

adb push /home/q/work/temp/test.mp3 /home/q/Music/m1-mipi-audio-test.mp3

Audio playback via GUI: In the Debian desktop, you can use the file manager to navigate to the Music directory and double-click m1-mipi-audio-test.mp3 to play it.

Audio playback via GStreamer command line: When playing audio from the command line, you can use the following command.

💡 It is recommended to run the following playback commands in the board’s graphical desktop terminal. If executed via an ADB root shell, audio playback may fail due to missing audio session environment variables.

In the board’s graphical desktop terminal (logged in as the q user), you can directly run:

gst-launch-1.0 playbin uri=file:///home/q/Music/m1-mipi-audio-test.mp3

If executing via an ADB root shell or SSH root login, first switch to the q user, then set the audio session environment variables in order, and finally run the playback command:

su - q
export DISPLAY=:0
export WAYLAND_DISPLAY=wayland-0
export XDG_RUNTIME_DIR=/run/user/1000
export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
gst-launch-1.0 playbin uri=file:///home/q/Music/m1-mipi-audio-test.mp3

The following is a screenshot of audio playback using the GStreamer command line.

In this test, audio playback via both the desktop file manager and GStreamer command line was verified, and the current audio output device played sound normally. If using an external Bluetooth speaker or other audio device, please confirm that the system sound output device is correctly selected.

Audio Output Check

If there is no sound during video playback, you can check the audio service and default output device in the board’s graphical desktop terminal:

pactl info

If multiple audio output devices exist in the system, you can switch the output device in the GNOME desktop quick settings (upper-right corner), or go to Settings > Sound to view the audio output configuration.

Advanced Features

HDMI Screen Hot Plug

HDMI supports hot-plug. After connecting an HDMI display while the system is running, the system typically auto-detects the display and outputs the image.

Hot-plug usage:

1. While the system is running, connect the HDMI display to the board’s HDMI interface.

2. Wait for the system to auto-detect the display device.

3. If the image does not appear automatically: go to Settings > Displays to check whether the display is recognized, or check /sys/class/drm/card0-HDMI-A-1/status to see if the display is detected.

4. To disconnect the HDMI display, simply unplug the HDMI cable.

Command-Line Status Check

Common troubleshooting commands:

# Check HDMI connection status and supported display modes
cat /sys/class/drm/card0-HDMI-A-1/status
cat /sys/class/drm/card0-HDMI-A-1/modes

# Check display-related information in system logs
journalctl -b | grep -Ei 'HDMI|drm|display|edid'

# Check audio default output device
pactl info

Application Scenarios

• Media entertainment terminal: Play video, music, or display images through the HDMI screen.

• Industrial data visualization platform: Used for displaying device status, sensor data, dashboards, and alarm information.

• Smart interaction terminal: Pair with a touch HDMI screen to implement local menus, control panels, and human-machine interaction interfaces.

• Development and debugging display terminal: After connecting a common HDMI display, you can directly view the Debian desktop and debugging information.

Troubleshooting

Symptom	Possible Cause	Solution
Black screen after boot	Display not powered, incorrect input source selection, HDMI cable not fully inserted, or system has not finished booting	Check display power and input source; re-plug the HDMI cable; check whether the system booted normally via serial port or ADB.
No image after hot-plug	System did not detect the HDMI device in time, or monitor EDID read error	Wait a few seconds and check the connection status: go to Settings > Displays to check the display, or run cat /sys/class/drm/card0-HDMI-A-1/status. If necessary, re-plug the HDMI cable or restart the system.
Abnormal resolution	Monitor EDID read error, poor cable quality, or the current monitor does not support the mode negotiated by the system	Replace the HDMI cable or monitor; go to Settings > Displays to manually select an available resolution, or run cat /sys/class/drm/card0-HDMI-A-1/modes to view currently available display modes.
Screen artifacts or flickering	Poor HDMI cable quality, loose connector contact, or interference	Replace with a better-quality HDMI cable; confirm the connector is fully inserted; keep the cable away from strong interference sources.
Touch unresponsive	USB touch cable not connected, connected to the wrong port, or system did not recognize the input device	Check the USB touch cable connection; run lsusb and cat /proc/bus/input/devices to see if the touch device is recognized.
Video cannot play	Video codec not supported by the current player, or incorrect file path	Confirm the video file exists in /home/q/Videos/; try using the GNOME video player or GStreamer to play a common H.264 MP4 test video.
Video has image but no sound	Incorrect audio output device selected, volume muted, or the monitor does not support the current audio output	Check the sound settings in the upper-right corner, go to Settings > Sound to switch the output device; run pactl info to view the default output device. Confirm the audio device is connected and volume is not muted.