For testing the Java Does USB library, a dedicated USB test device is needed. This is the code for an STM32F103C8 microcontroller. This microcontroller is found on many inexpensive development board, most notabily on the so called Blue Pill. Such boards are available for about 3 USD, including the required ST-Link programmer.
All data sent to endpoint 0x01 (OUT) is sent back on endpoint 0x82 (IN). Both endpoints use bulk transfer with a maximum packet size of 64 bytes. The device uses an internal buffer of about 500 bytes. Up to this amount, the data can be first sent and then received.
Several vendor-specific control requests are supported for testing:
bmRequest |
bRequest |
wValue |
wIndex |
wLength |
Data | Action |
|---|---|---|---|---|---|---|
| 0x41 | 0x01 | value | 0 | 0 | none | Host to device: value is saved in device |
| 0x41 | 0x02 | 0 | 0 | 4 | value (32-bit LE) | Host to device: value is saved in device |
| 0xC1 | 0x03 | 0 | 0 | 4 | value (32-bit LE) | Device to host: saved value is transmitted |
This project requires PlatformIO. The easiest way to get up and running is to use Visual Studio Code and then install the PlatformIO IDE extension.
After the extension is installed, open this folder and then click checkbox icon (Build action) in the status bar.
To upload the code to the microcontroller:
- Connect the ST-Link programmer to the development board
- Connect the ST-Link programmer to your computer
- Click the arrow icon (Upload action) in the status bar
The directory bin contains a pre-built firmware. In order to upload it, a utility is needed, either STM32CubeProgrammer (requires an STM account, does not properly work on macOS) or the open-source ST-Link command line utility. See the respective web site for installation instructions.
If the commmand line utility is used, run these commands to upload it:
cd stm32-loopback/bin
st-flash write firmware.bin 0x08000000