Practical Raspberry Pi Linux Compilation Guide

1.1 Burning Software

1.2 Downloading the Image File

1.2.1 Image File Download Link

For the image file, it is recommended to use the 32-bit version, but the 64-bit version can also be used.

Note: If you want to use a graphical interface, please select the desktop version of the image file when downloading, preferably with commonly used software, and try to use the 32-bit version, as I have not successfully compiled the 64-bit version.

Image file download link:https://www.raspberrypi.com/software/operating-systems/

1.2.2 High-speed Download Tool

If the download speed is slow, you can first download a tool called Motrix, and then open the download link with it.

Motrix download link:

https://motrix.app/zh-CN/

1.3 Burning Process

After downloading, select Use Custom Image, then insert the SD card and proceed with the burning.

Special Reminder: It is best to use an SD card of at least 32G; 16G is also acceptable, but it is recommended to choose a faster SD card, as the entire system’s burning and writing, including the subsequent compilation, are completed on the SD card.

2.1 SSH Method

After burning is complete, the SD card will be divided into two partitions: one is a system partition that cannot be opened, and the other is a file system partition that can be opened.

If you did not enable SSH in the official burning tool beforehand, you need to open that file system partition on your computer and create a new file named SSH without any file extension.

After creating the file, insert the memory card into the Raspberry Pi, connect an Ethernet cable to the router for the Raspberry Pi, power it on,the official recommended power supply for the Raspberry Pi is 5V3A(Note: If the power supply is less than this and you have multiple devices connected, including a screen, it may cause unstable power supply leading to module restarts and other issues).

Next, open your router management backend and find the Raspberry Pi. If you set the name for the Raspberry Pi in the previous step, it should be easier to find. If not set, the default name for the Raspberry Pi is raspberry, and the default password for the root user is also raspberry.If you are using the Raspberry Pi for a long time, it is recommended to assign a static IP.

The management interface on my side looks like this:

Compilation can be either local or cross-compilation, both of which are possible. Local compilation means the Raspberry Pi compiles itself, while cross-compilation means using another machine with better performance than the Raspberry Pi (like your own computer) to compile the drivers, and then replacing the compiled kernel onto the SD card before inserting it back into the Raspberry Pi.

This article will only explain the local compilation method:

5.1 Local Compilation

The advantage of local compilation is that it does not require too many commands, making it friendly for beginners.

The downside is that it is limited by the Raspberry Pi’s weak performance, making the compilation speed painfully slow. If all four cores are open, compiling once takes about one to two hours.If you use the default compilation command and only open one core, I have tried it once, and it took about four hours.

5.1.1 Downloading the Linux Kernel Source Code

Open the command line, navigate to the directory you want, such as the desktop or dowon, you can also create a new directory, but remember not to write in Chinese, then use the following command to download the latest kernel for the Raspberry Pi.

-depth=1 means a shallow copy, only cloning the current project’s code without historical modification records. The common git clone is a deep copy, containing all operations since the repository was initialized.

We are only learning/compiling the current version of the kernel and do not need to look at those things. If we cloned everything, it would be over 3G, and downloading without a proxy would take a long time, even if using a free proxy, most have a maximum repository limit of 2G.

The original repository is here:

https://github.com/raspberrypi/linux

5.1.2 Modifying the Corresponding Driver Files

If using the SSH command line to modify, you can use the nano editor to modify files. Remember to enter su to become a superuser first, otherwise the modifications may fail. (Note: If you have encountered Linux in college, you should know about VI and VIM editors, both can be used, but nano is a bit easier.)

The specific commands are as follows:

5.1.2.1 Modifying the option.c File

sudo nano drivers/usb/serial/option.c — use the nano editor to enter the option.c file

Remember: Do not use the mouse to scroll up and down in the file, use the keyboard’s up and down keys! Using the mouse will cause a bunch of ^H^L to be input into the corresponding file.

Modifications needed in the option.c file:

First Modification:

Under the static const struct usb_device_id option_ids[] function, add a line below the “{“.

Second Modification:

In the static struct usb_serial_driver option_lport_device function, add a line below the last line: .resume = usb_wwan_resume.

Third Modification:

Under the line struct usb_interface_descriptor, add a line.

Fourth Modification:

Under the line If (iface_desc->bINterfaceClass to return -ENODEV;, add the following lines:

After completing the modifications, use ctrl+o to save the changes and ctrl+x to exit the file editor.

5.1.2.2 Modifying the usb_wwan.c File

Use: sudo nano drivers/usb/serial/usb_wwan.c — use the nano editor to open the usb_wwan.c file.

There is only one modification in this file:

In the static struct urb *usb_wwan_setup_urb function, after the line if (intfdata->use_zlp to PACKET;, add the following lines:

After completing the modifications, use ctrl+o to save the changes and ctrl+x to exit the file editor.

At this point, the driver modifications are complete, and you can enter the kernel editing interface, mainly to configure some features that are not enabled by default, such as ECM/PPP.

5.1.3 Preparing for Compilation Before Code Modifications

First, install Git and build dependencies:

Check the version of the Raspberry Pi you have and whether the downloaded system version is 32-bit or 64-bit, and choose the corresponding command below.

If you are already in the Linux directory, you do not need the first command cd linux.

1) For Raspberry Pi 1, Zero, and Zero W, as well as Raspberry Pi Compute Module 1, default (only 32-bit) build configuration:

2) For Raspberry Pi 2, 3, 3+, and Zero 2 W, as well as Raspberry Pi Compute Module 3 and 3+, default 32-bit build configuration:

3) For Raspberry Pi 4 and 400, as well as Raspberry Pi Compute Module 4, default 32-bit build configuration:

4) For Raspberry Pi 3, 3+, 4, 400, and Zero 2 W, as well as Raspberry Pi Compute Module 3, 3+, and 4, default 64-bit build configuration:

If any of the above commands report an error, you can search for solutions on Baidu or consult Hezhou FAE.

5.1.4 Kernel Configuration

In the Linux path, enter:

Enter the kernel configuration interface. If you cannot enter, first check whether your current user is a superuser. If not, enter su to become a superuser; then proceed to config.

In the kernel configuration interface, press “/” to search for the place you want to modify. For example, when searching for RNDIS, if there are many related configuration items, you can scroll the mouse to view in this interface, ensuring that the status of the options related to RNDIS is y or m:

Below are the paths of the related configuration items:

ECM/PPP/CMUX works the same way; for CMUX, make sure to search for N_GSM:

You can select a project, configure it, and then press the left and right keys to choose Save to save the configuration. After checking all options, press the left and right keys to select Exit, until a dialog box pops up asking whether to save. Select yes to save the configuration, and you are done with all configuration work.

5.1.5 Building the Kernel

Generate and install the kernel, modules, and device tree blob. This step may take a long time, depending on the Raspberry Pi model used.

For 32-bit kernels:

For 64-bit kernels:

Note 2: -j4 indicates that four cores will be started to compile together.

Remember to put a fan on the Raspberry Pi for cooling, as it can get very hot.

Once all projects are completed, restart, and your Raspberry Pi should be running your newly compiled kernel!

Insert the Hezhou Air724/Air780E/1802/1603 series board into the Raspberry Pi, power it on, and enter:

You should see three ports:

Note 1: These three ports are assigned by Linux; the port numbers may not be fixed. If you want to fix the port numbers, you can use the solution mentioned in this link:

https://doc.openluat.com/article/2080/0

Note 2: The 618 may not be named ttyUSB; it could be ttyACM or something else:

There are many serial debugging tools under Linux, the most well-known being minicom. The simple usage method is as follows:

I personally find it not very user-friendly, so I use our own serial tool, the usage method is as follows:

https://doc.openluat.com/article/645/0

After compilation, an executable file named at.out will be generated in the directory. Here is an example of usage:

5.2 Possible Issues After Compilation

5.2.1 Cannot Find Port

If lsusb can display the corresponding module’s PID VID but cannot find those virtual serial ports.

Solution: Send the command

1) For 8910 series Air724UG/720UH/720UG/722UG/820UG/600UG… send this:

Then check for the port again. If found, it proves that the PID VID modification was unsuccessful, and you need to start again from 5.1.1.

If lsusb cannot find the corresponding port, first check whether the module’s vdd_ext has voltage when powered on. If not, connect powerkey to ground and supply 4V to vbat; if there is voltage, it is recommended to pull out four wires for vbus, DM, DP, and gnd, and connect a USB cable to a Win10 computer. After powering on the module, see if there are three ports on the Win10 computer.

5.2.2 Abnormal Port Display

If lsusb shows the port as 17d1 0001 instead of 19d1 0001.

Solution: 17D1 0001 is the port number displayed by the 618 module after entering boot in Linux. Usually, simply rebooting the 618 module will solve the problem.

If after rebooting it still shows 17D1 0001, it indicates that the vdd_ext pin and uboot pin are shorted together, or the uboot pin is connected to another high-level pin such as 3.3V or vbat.

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