2003 CM4 Tiny HDMIx2(Dual HDMI Expansion Board)

Keywords

Raspberry Pi, CM4 Core board, System Flashing, 4G, RPiOS, eMMC, Dual HDMI, Dual-screen different display

Ⅰ、Introduction

The CM4_Tiny dual HDMI expansion board is designed based on the Raspberry Pi CM4 core board and is a expansion board for applications such as media players, dual-screen different displays, image and video capture, human-computer interaction, remote control, and more.

The CM4_Tiny dual HDMI expansion board has two full-sized HDMI ports, which can be used to output different content to two display devices, and it supports 4K output. It also has native Gigabit Ethernet and a native USB host port, and it includes a reserved 22-pin 0.5mm CAM interface, which can be used to connect various cameras for image and video capture and processing. In addition, there is a 2.54mm pitch 2x6 GPIO header, it is containing I²C, UART, and SPI signals, which can be used for conventional peripheral expansion.

The CM4_Tiny dual HDMI expansion board is powered by a USB-C port at 5V3A.

Ⅱ、Hardware Resources

1. One native Gigabit Ethernet port, using an integrated transformer, which provides better electromagnetic performance.

2. Two standard HDMI ports, supporting 4K output.

3. One native USB OTG A port (an USB A-A cable can be optionally used to flash system for the eMMC version of the core board via this host port).

4. One camera CSI interface, 22-pin with 0.5mm pitch, with an optional flexible flat cable adapter from 1mm 15-pin to 0.5mm 22-pin.

5. The 12-pin GPIO is broken out, containing I2C, UART, and SPI signals, 2.54mm.

6. One USB-C power supply interface, 5V3A, supporting PD protocol chargers.

Ⅲ、System flashing and setting

3.1 Overview

This document uses the Raspberry Pi OS and OpenWrt system for testing.

The version of the Raspberry Pi OS is: 2024-07-04-raspios-bookworm-arm64.img.xz

You can download the Raspberry Pi OS in:

https://www.raspberrypi.com/software/operating-systems/#raspberry-pi-os-64-bit

The version of the OpenWrt is: openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade-linux-6.1.100-20240805.img.gz

3.2 Boot from TF card

If the core board does not have an eMMC, the system will boot from the TF card.

3.2.1 Use the Imager to flash the system

First, install the Imager on the Windows. You can download it in: https://www.raspberrypi.com/software/

Insert the TF card into the card reader after installation, plug the card reader into the PC's USB port, and then open the software.

Raspberry Pi Device: Choose Raspberry Pi 4；

Operating System:

Choose Raspberry Pi OS(64-bit), to flash the system image downloaded from the Raspberry Pi official website (internet connection required).

Choose Use Custom, to flash the system image already downloaded onto the hard drive (no internet connection required).

Storge: Select the TF card that needs to be flashed (i.e., the card inserted into the PC's USB port).

After making your selection, press "NEXT." It is recommended to click "Edit Settings" to pre-set some parameters in the flashing software. This way, you won't need to set them again when the system starts up, making it easier to use.

If you need to use the pre-set settings, press "Yes"; if you do not need to use the pre-set settings, press "No". Proceed to the next page, and click "Yes" to start the flashing and verification process. After the flashing is complete, follow the prompts to remove the card.

The above instructions describe how to flash the Raspberry Pi OS. For flashing the Ubuntu system or the OpenWrt system, similar operations are used; when you reach the step "Operating System", you need to select Use Custom, and then choose the pre-downloaded image.

3.2.2 Use the balenaEtcher to flash the system

First, install the balenaEtcher on the Windows. You can download it in: https://etcher.balena.io/#download-etcher

Insert the TF card into the card reader after installation, plug the card reader into the PC's USB port, and then open the software.

Flash from file: Select the pre-downloaded Raspberry Pi OS or Ubuntu system image.

Select target: Select the TF card that needs to be flashed (i.e., the card inserted into the PC's USB port).

Then click "Flash!" to start the process, and wait for it to complete.

3.2.3 Boot the system

Remove the TF card from the card reader, insert it into the TF card slot of the Raspberry Pi, and power the board on to enter the system.

3.3. Boot from eMMC

If the core board has onboard eMMC, the system will ignore the TF card and boot from the eMMC instead.

To flash the system to the eMMC, you need to install the driver package on the PC first. You can download it in:

http://www.mcuzone.com/down/Software.asp?ID=10000623

Then use a jumper cap to short the BOOT pin and the GND pin on the expansion board (located between the two HDMI ports):

Use a USB Type A-A data cable to connect the USB OTG port (i.e., the USB-A port on the expansion board) to the computer.

After connecting to the computer, open the Computer's Device Manager and check if a new USB device appears. In the image below, it is a USB device named "BCM2711 Boot":

Under All Programs in the PC's Start menu, there is a shortcut called rpiboot under Raspberry Pi.

Open this software, and the computer will format and partition the eMMC or TF card:

Wait a moment; a partition will appear in the File Explorer (in this example, the partition is named bootfs, but the actual name may vary):

Then, we can use the balenaEtcher software to flash this partition.

Open the balenaEtcher software, first, click "Flash from file" and select the file you want to flash to the eMMC. then, choose the bootfs partition mentioned above, and click "Flash!" to start flashing the file:

After the flashing is complete, we need to remove the jumper cap that was previously connected; otherwise, the core board will not start normally. Then, power the system on, and wait for it to boot up.

Ⅳ、Hardware testing under Raspberry Pi OS

4.1 Native Gigabit Ethernet port test

Plug the Ethernet cable into the native Gigabit Ethernet port. The system will automatically acquire an IP address. Open the terminal and install the speed testing software iperf3.

sudo apt-get install iperf3

Then we use iperf3 for testing.

The speed test results for the native Gigabit Ethernet, with the client mode showing about 942Mbps:

The server mode showing about 949Mbps:

Note: The speed of the native Gigabit network test can be affected by the network environment and the testing method. Speeds should be considered based on actual results; this test is for reference only.

4.2 CSI test

First, connect the camera to the CAM1 interface (this document uses the OV5647 camera):

After connecting everything, power on the board. Once the system is running, open the terminal and run the following command:

sudo nano /boot/firmware/config.txt

Add the following statements at the end of the file:

dtoverlay=ov5647,cam0

dtoverlay=ov5647,cam1

In actual use, add according to your model, save the changes, and then restart the system to be able to use the OV5647 camera.

After rebooting, enter the following command in the terminal:

ls /dev

Then you will be able to see the video0 device.

Enter libcamera-hello --camera 0 in the terminal to open the corresponding camera for viewing.

If you need to take a photo, enter:

libcamera-jpeg -o test.jpg

The photo is saved in the /home/mcuzone directory (which is the home directory), and the photo effect is as follows:

4.3 Dual HDMI test

将扩展板上的两个HDMI口各插一个显示器，可实现一主一副双屏扩展显示，先插入的显示器为主屏。

点击左上角的树莓派标志，Preferences下有个Screen Configuration：

打开软件后，可以在里面调节双屏的相对位置、分辨率、转向、刷新率等参数：

4.4 扩展4G模组测试

本扩展板有2个版本，连接4G模组的方法如下：

1. 如果你是A版本扩展板，用一根USB Type C-A线，将4G模组接到扩展板的USB Type A口；

2. 如果你是B版本扩展板，4G模组的1.25 4pin接口接到扩展板内置的1.25 4pin USB口，同时可以装进外壳。

下图左为A版本，右为B版本：

无论用哪种方法，都会占用扩展板的USB Type A口，因此此时无法使用键盘鼠标，需要用SSH软件通过网口去操作系统。

如果有必须使用键盘鼠标的需求，可以在扩展板A版本上接一个USB HUB，然后把4G模组和键鼠都接在USB HUB上。但是因为4G模组的能耗较大，因此建议使用带外接电源的USB HUB。

本文档使用的4G模组型号为CM4 4G mini（国产CAT4）。

正确连接扩展板和4G模组后，启动系统，在SSH软件中执行命令lsusb，如下图所示：

本模块的id为1286 4e3d。

在SSH软件中执行ifconfig -a，我们可以看到4G模块（eth1）已经正确获得了IP地址：

4G模组正确获得ip地址后，我们可以ping外网地址，如：

ping www.mcuzone.com

表示此时已经可以正常上网。

五、OpenWrt系统下的硬件测试

此扩展板搭配树莓派CM4核心板，在OpenWrt系统下可配置为一进一出的交换机模式：

方式一：扩展板上扩展4G模组可作为WAN口（直接4G上网），网口配置为LAN口，用于连接PC（4G进，有线网口出）。

方式二：CM4核心板自带的WiFi配置为WAN口（需要是带WiFi版本的CM4核心板），扩展板上网口配置为LAN口（WiFi进,网口出）。

本文使用的OpenWrt系统为：openwrt-bcm27xx-bcm2712-rpi-5-squashfs-sysupgrade-linux-6.1.100-20240805.img.gz

5.1 准备工作

烧写OpenWrt系统并上电启动后，我们通过扩展板自带网口连接网线至PC网口，待PC的网卡与扩展板的网口连接成功后，我们在Windows设置中找到网络和Internet，在以太网中打开连接的网络查看默认网关的IP地址，这个地址就是OpenWrt系统的后台配置页面地址，如图所示，本文测试的地址为192.168.198.1：