Debugging problems with STM32F4 VCP

        The board has been made, and its function is: accurate positioning using sensors and GPS. The board uses the debugging STM32F4 VCP, which is USB to serial port. The problems and solutions that occurred when transplanting ST official programs are listed below:

1. Because the download interface is 5-pin SWD, and the downloader is st-link v2  ST-LINK/V2 . First of all, we need to figure out how to connect the SWD interface and st-link v2. The key point here is to connect the VCC pin of SWD to the first pin of st-link v2. If it is not connected in this way, an internal command error will occur. This error sometimes occurs because of a reset problem. If the download can be carried out normally, then the following problems will be easy to solve! I was entangled here for a long time.

2. Check whether the crystal oscillator of the board is oscillating, and measure it with an oscilloscope. The modification places are HSE_VAlUE and PLL_M in system_stm32f4xx.c.

3. Because the default USB configuration of ST company uses high-speed USB port, we need to remove the macro definition of HS in the c/c++ option of keil options. As shown below:

           4. When configuring your own serial port, pay attention to which serial port to use, the baud rate (LINE_CODING linecoding), the serial port clock enable function, and the serial port interrupt. There must be an interrupt program. If there is no interrupt program, the program will freeze when it runs to B.ENDP ALIGN of startup_stm32f4xx.s.

           5. If the program cannot run after jumping to 0x08001460 BEAB BKPT 0xAB, you need to set the microlibrary Use MicroLIB.