Stm32 Virtual Com Port Device Driver For Mac

16-04-2021
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This USB driver (STSW-LINK009) is for ST-LINK/V2, ST-LINK/V2-1 and STLINK-V3 boards and derivatives (STM8/STM32 discovery boards, STM8/STM32 evaluation boards and STM32 Nucleo boards). It declares to the system the USB interfaces possibly provided by the ST-LINK: ST Debug, Virtual COM port and ST Bridge interfaces.

  • This core will allow you to use BSFrance AVR based boards with the Arduino ecosystem, it ibsed on STM32 HAL. At first drivers for the usb-serial (VCP, Virtual Com Port) and DFU (Device Firmware Upgrade) have to be installed. This applies to Windows only, Mac OSX and Linux users wont have to install drivers (in most cases).
  • The problem raises when I try to use the Virtual COM port on MAC OS X. The device is recognized as 'tty.usbmodemxxx' when I try to send/receive any byte it the ZTerm (used for testing purposes) returns me that the USB Port is busy/not available. I used my own tool and the FileDescriptor returns always -1 so it is not possible to access to it.

As I continue my journey with STM32 development, I wanted to share my findings with how to get a Virtual COM Port (VCP) working with a Nucleo board.

Specifically, I’m using the Nucleo-F042K6, as it has a built-in USB device peripheral (full speed), and it does not require an external crystal. I highly recommend looking over the USB Hardware and PCB Guidelines document from ST Microelectronics to learn about what’s needed for your particular STM32 part. Note that if you are using a Nucleo board with an STM32F401 or STM32F411, you will need to solder an external crystal to the board, as it is unpopulated on those boards.

To begin, strip a USB cable or get a USB breakout board (like this one from SparkFun) and connect the lines to a breadboard as shown in the Fritzing diagram below. Make the following connections:

  • VUSB → Diode → Nucleo 5V (don’t want to short something if we’re plugging in 2 USB cables!)
  • USB D- → Nucleo D10 (PA11)
  • USB D+ → Nucleo D2 (PA12)
  • USB GND → Nucleo GND
  • USB GND → USB Shield (don’t know if this is necessary, but it makes me feel better)

Also, this is super important: remove the jumper that comes default on your Nucleo board! It bridges D2 and GND and will short out our D+ line if left in place.

Plug the two USB cables from the Nucleo board into your computer. We’ll be sending our compiled program over to the ST-LINK side of the board, and the VCP will enumerate on the USB lines that we just added. I don’t have a bootloader working (yet) to where we can send binary files over VCP, but that’s on my to-do list.

For this, I’m using STM32CubeIDE along with the STM32F0 HAL API.

Stm Virtual Com Port Driver

In STM32CubeIDE, start a new project (File > New > STM32 Project). Choose your part or board. I’ll pick the Nucleo-F042K6, since that’s the board I have.

On the next screen, give your project a useful name (such as “nucleo-f042k6-vcp-test”). Leave everything else as default. We’ll be using C as our language for this example. Click Finish, and you’ll be asked a few questions:

  • Yes to “initialize all peripherals with their default Mode”
  • Yes to “open this perspective now”

In the CubeMX configuration perspective, you’ll need to enable a few options to initialize the USB as a Virtual COM Port. In the Pinout & Configuration tab, go to Categories > Connectivity and click USB. Enable Device (FS). You should see PA11 and PA12 be automatically configured for USB_DM and USB_DP.

Under Categories > Middleware, select USB_DEVICE. Change Class For FS IP to Communication Device Class (CDC). This tells the USB stack that we want to enumerate as a CDC device, which will allow us to send serial data to and from our computer across the USB lines.

Click on the Clock Configuration tab. The software will tell you that your clocks have issues. By default, the Nucleo-F042K6 board is configured for 8 MHz clocks for almost everything. We need to bump those up to 48 MHz for USB to work. Luckily, you can just click Yes on the pop-up when asked to run the automatic clock issues solver. This should automatically change all of the necessary clocks to 48 MHz.

In the Project Manager tab, change the Minimum Heap Size to 0x100. The STM32F042K6 comes with 6 kB of RAM, which isn’t a whole lot. USB functionality takes up probably 2-3 kB worth of that memory, so we need to be careful about how we use the rest.

We can free up some space by adjusting the minimum heap and stack sizes. These parameters essentially reserve sections of data memory for the heap and stack. By setting 0x200 and 0x400, we’ve told the processor to reserve 1 kB of RAM for the heap and stack, respectively. We need to lower one of them in order to accommodate the USB functions. I chose heap, as it seems less likely we’ll be using dynamically allocated memory for this application.

If you get an error message like `._user_heap_stack’ will not fit in region `RAM’ or region `RAM’ overflowed by 64 bytes when you compile, it means you are running out of RAM in your application. You will need to go into the Device Configuration Tool (the .ioc file) and adjust the stack and heap settings as described above. Alternatively, you can go into the .ld linker script and look for the _Min_Heap_Size and _Min_Stack_Size settings there (just know that this file will be overwritten if you make changes in the graphical Device Configuration Tool).

Click File > Save to save the changes to the CubeMX configuration. You’ll be asked if you want to generate Code. Click Yes.

Stm32 virtual com port

In your project files, navigate to the Src directory. Notice that you have several USB-related files that have been added. usbd_cdc_if.c contains the functions that allow us to send and receive serial data using the USB Communication Device Class. Feel free to peek in there, if you wish.

Open up Src > main.c. At the top, under /* USER CODE BEGIN Includes */ , enter the following line:

Stm32 Virtual Com Port Device Driver For Mac

This will let us call functions from the CDC library. Scroll down to our while(1) loop in main. Under /* USER CODE BEGIN 3 */ (but still inside the while loop), enter the following:

Here, we create a simple string and call a USB CDC function to send out that string over the USB lines. We then wait for 1 second before repeating this action ad infinitum.

Click Project > Build All to build the project. Click Run > Debug As > STM32 MCU C/C++ Application. A pop-up window will appear asking you to create a new launch configuration. Note that if you are not using a Nucleo board or an ST-LINK, you can change the hardware debugger (e.g. to a Segger J-LINK) in the Debugger tab. If you are using a Nucleo, leave everything as default and click OK.

Com

If asked to switch to the Debug perspective, click Switch. When the new perspective opens, click Run > Resume (or the play button on the toolbar).

Your code should now be running, and the microcontroller will enumerate as a USB device! Feel free to verify the new serial port in your OS’s device manager. This should show up as a USB serial or COM port.

Open your favorite serial terminal program, and enter the following connection details:

  • Port: USB serial or COM port discovered above
  • Baud rate: 9600
  • Data bits: 8 (default)
  • Parity: None (default)
  • Stop bits: 1 (default)

Open the serial connection, and you should be greeted by that oh-so-familiar phrase, repeating over and over again:

When you’ve had enough strings, feel free to press the stop button in the IDE to stop the program from running on the STM32.

Interestingly enough, the STM32 seems to support autobaud detection by default. Try changing the serial terminal’s baudrate to anything else and see if you can still receive text. I bet that disabling autobaud would save some RAM, but I have not discovered how yet.

From what I understand, CDC_Receive_FS() is a callback, so you’ll need to change its definition in usbd_cdc_if.c to get it to work. I haven’t played with it yet, so that’ll be a post for another time.

I hope that this helps you get started with your STM32 USB journey!

The Communication Device Class (CDC) is used for implementing virtual communication ports. This example demonstrates a bridge between a Virtual COM Port on the USB Host Computer and an UART port on the evaluation board.

The following picture shows an exemplary connection of the development board and the USB Host Computer.

The Abstract.txt file contained in the Documentation group of the Project window gives you more information on the general setup and the available I/O on the development board.

Driver

Stm32 Virtual Com Port Device Driver For Macbook Pro

Open the example project in MDK. The µVision Project window should display a similar project structure:

Source Files

Stm32 Virtual Com Port Driver Mac

  • VirtualCOM.c contains the main C function that initializes the board hardware and the USB Device Component. Furthermore, it contains the code that exchanges the data internally between the USB and the UART port.
  • The USBD_User_CDC_0.c is an adapted code template that implements all necessary file access functions. Refer to CDC: Communication Device Class (ACM) for details about these template functions.

If you are using RTOS other than CMSIS-RTOS2 RTX5 for your project please make sure to satisfy USB Device Resource Requirements.

You may now build and download the example project to the evaluation board using the µVision commands:

  • Project –> Build target (F7)
  • Flash –> Download (F8)

After these steps, the project should start executing on your evaluation kit. In case of errors, refer to the Evaluation Board User's Guide for configuration information.

Stm32 Virtual Com Port Driver 1.5

Hardware Setup

The setup of the Evaluation Board hardware is described in the Abstract.txt file.

  • Verify all jumper settings on the target hardware.
  • Connect the UART on the development board to your PC (you might need an USB to serial RS232 adapter). Use an USB cable to connect your development board to the Host PC and power up your board.
  • The Welcome to the Found New Hardware Wizard appears. Installation of the driver is described in detail in the Abstract.txt file.

PC Software

The USB Device Virtual COM example can be tested on a Windows PC using a terminal emulation program. Since Hyperterminal in not part of Windows any more, please download an appropriate program for this purpose (such as PuTTY for example). Open the two COM ports 'COMx' and 'COMy'. Any data from 'COMx' will be echoed on 'COMy' and visa versa:

About Host PC driver for Microsoft Windows

The example folder contains two files relevant for driver installation on the Microsoft Windows:

  • Driver setup information file (xxx-vcom.inf) which is used to create a digitally signed driver catalog file (xxx-vcom.cat)
  • Digitally signed driver catalog file (xxx-vcom.cat)

The driver files are provided as an example, the driver setup information file should be adapted and digitally signed driver catalog file should be created from adapted driver setup information file.

Driver setup information file should be adapted in the following way:

  • c251 in Vendor ID VID_c251 entries should be changed to the vendor ID number assigned to your company by the USB organization (c251 Vendor ID is reserved for Keil Software and should not be used)
  • xxxx in Product ID PID_xxxx entries should be changed to the product ID as assigned by your company
  • in [DeviceList.xxx] sections, entries not relevant for the device, should be removed or added as described below:
    • if device is pure CDC class device (not composite) then all entries ending with &MI_xx should be removed
    • if device is a composite device with one or more CDC class instances then entries not ending with &MI_xx should be removed and entries ending with &MI_xx should exist for each CDC class instance (example driver contains entries ending with &MI_00 and &MI_02 which are used for composite device containing two CDC class instances and each instance uses 2 interfaces where MI_00 describes first CDC instance and MI_02 entry describes second CDC instance)
  • [Strings] section should be changed as desired
Note
Vendor ID and Product ID are configured in the USBD_Config_n.c configuration file of the embedded application.
For producing digitally signed driver catalog file please refer to Microsoft Windows documentation.