The development of embedded software is inseparable from the development board. Without physical development boards, similar virtual machines like QEMU can be used to simulate the development board. QEMU is a virtual machine that supports cross-platform virtualization. It can virtualize many development boards. To facilitate the experience of RT-Thread without a development board, RT-Thread provides a board-level support package (BSP) for QEMU-simulated ARM vexpress A9 development board.
The board-level support package (BSP) provided by RT-Thread simulates ARM vexpress A9 development board is located in the bsp/qemu-vexpress-a9 folder under the BSP directory of RT-Thread source code. This BSP implements LCD, keyboard, mouse, SD card, Ethernet card, serial port and other related drivers. The contents of the folder are shown in the following figure.
The main files and directories of qemu-vexpress-a9 BSP are described as follows:
| Fles/Directories | Description |
|---|---|
| .vscode | configuration file of vscode |
| applications | User application code directory |
| drivers | The underlying driver provided by RT-Thread |
| qemu.bat | Script files running on Windows platform |
| qemu.sh | Script files running on Linux platform |
| qemu-dbg.bat | Debugging script files on Windows platform |
| qemu-dbg.sh | Debugging script files on Linux platform |
| README.md | Description document of BSP |
| rtconfig.h | A header file of BSP |
Type the menuconfig command in the Env terminal to enter the configuration interface, and then configure the BSP:
You can use the keyboard ↑ key and ↓ key to look up and down menu items, use the Enter key to enter the selected directory, use the Space key to select or cancel bool variables, and use the Esc key to exit the current directory.
If a package is selected in menuconfig, download the package using the pkgs --update command.
The alternative and recommended way is by using menuconfig -s to select the Auto update pkgs config feature, so that when users exit the menuconfig, Env will automatically download and update software packages.
Compile using the scons command, or scons -j12 means 12 CPU cores compiling.
Open the Env folder and double-click the env.exe file to open the Env console:
Switch to the QEMU BSP directory and enter the scons or scons -j12 command to compile the project. If the compilation is correct, the rtthread.elf file will be generated in the BSP directory, which is a target file required for QEMU to run.
After compiling, type qemu.bat to start the virtual machine and BSP project. qemu.bat is a Windows batch file. This file is located in the BSP folder, mainly including the execution instructions of QEMU. The first run of the project will create a blank sd.bin file under the BSP folder, which is a virtual SD card with a size of 64M. The Env command interface displays the initialization information and version number information printed during the start-up of RT-Thread system, and the QEMU virtual machine is also running. As shown in the following picture:
RT-Thread supports Finsh, and users can use command operations in command line mode.
Type help or press Tab to view all supported commands. As shown in the figure below, commands are on the left and command descriptions are on the right.
For example, by entering the list_thread command, you can see the currently running threads, thread status and stack size; by entering the list_timer, you can see the status of the timers.
Type list_device to view all devices registered in the system. You can see the virtual SD card "sd0" device as shown in the following picture. Next, we can format the SD card using the mkfs sd0 command, which will format the SD card into a FatFS file system. FatFs is a Microsoft fat-compatible file system developed for small embedded devices. It is written in ANSI C, uses abstract hardware I/O layer and provides continuous maintenance, so it has good portability.
For more information on FatFS, click on the link: http://elm-chan.org/fsw/ff/00index_e.html
The file system will not be loaded immediately after the first formatting of the SD card, and the file system will be loaded correctly only after the second boot. So exit the virtual machine, and then restart the virtual machine and project by entering qemu.bat on the Env command line interface. Entering ls command, you can see that the Directory directory has been added, the file system has been loaded, and then you can experience the file system with other commands provided by RT-Thread:
- ls: Display file and directory information
- cd: Switch to the specified directory
- rm: Delete files or directories
- echo: Writes the specified content to the target file
- cat: Displays the details of a file
- mkdir: Create folders
Please enter help to see more commands.
Open the Env tool in the BSP directory and enter the menuconfig command:
You can configure more functions in the configuration interface. After the configuration is completed, save the configuration first, and then exit the configuration interface:
- If you choose a package, you need to use the command
pkgs --updateto download the package. - Compile with
sconsorscons -j12. - Then enter
qemu.batto run. - Use
helpto view all commands of the BSP. And then use the commands.