STM32-RTOS-USB-HowToFix

Some useful tips to survive on STM32 using RTOS and USB CDC device

After a week of wasting time around ST generated code (for STM32H7) I have solved many problems, below a collection of my experience to solve many issues. Remember that afetr many fixes, if you generate code again, you lost all patches and you have to start again.

STM32CubeIDE and STM32CubeMX generates code for USB management that has malloc inside interrupt (bad practice) this can generate HEAP corrution, also some ST versions of FREERTOS doesn't manage memory correctly for a multithread enviroment.

1. If you use or don't use USB and you have problems with FREERTOS, memory management may be the problem
   Try to use heap_useNewlib.c by Dave Nadler instead of \Middlewares\Third_Party\FreeRTOS\Source\portable\MemMang\heap_4.c also take a look at http://www.nadler.com/embedded/newlibAndFreeRTOS.html for a very well explanation and also http://www.nadler.com/backups/20200111_draft2_STM_Cube_Issues_and_Workflow.html

2. Try to increase HEAP and STAK inside .ld file or by CodeGeneratore. Put HEAP to 0x400 or more and Stack to 0x800 for example, but be free to try whai is best for you.

3. USB code uses malloc inside interrupt, best is to replace malloc with a static struct. Look PDF UM1734 STM32Cube™ USB device library at point 6.7 Library footprint optimization, this will be a fist step to impruve the code.

4. On Windows 10 there are many problems opening a VCP, this is because the driver returns a bad parameters of VCP configuration, so in this situation the problem is not a memory management problem
   In file usbd_cdc_if.c, inside Private Variables section, declare
   static uint8_t uartcfg[7] = {0,0,0,0,0,0,0};
   then inside function CDC_Control_FS

    case CDC_SET_LINE_CODING:
      	uartcfg[0] = pbuf[0];
      	uartcfg[1] = pbuf[1];
      	uartcfg[2] = pbuf[2];
      	uartcfg[3] = pbuf[3];
      	uartcfg[4] = pbuf[4];
      	uartcfg[5] = pbuf[5];
      	uartcfg[6] = pbuf[6];
    break;

    case CDC_GET_LINE_CODING:
      	pbuf[0] = uartcfg[0];
      	pbuf[1] = uartcfg[1];
      	pbuf[2] = uartcfg[2];
      	pbuf[3] = uartcfg[3];
      	pbuf[4] = uartcfg[4];
      	pbuf[5] = uartcfg[5];
      	pbuf[6] = uartcfg[6];
    break;

this will prevent Windows 10 to take error opening CDC Virtual Com Port

5. Inside sysmem.c there is a function caddr_t _sbrk(int incr) that should be used for malloc but is never actually called so I think something is changed in memory management. Need to be investigated if there is some new code improvements