Redirect-printf-to-USB-VCP-on-STM32H7-MCU

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Redirect-printf-to-USB-VCP-on-STM32H7-MCU

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Enable printf() function to work with USB Virtual COM Port (STM32H743ZI)

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# Redirect printf() to USB Virtual COM Port on STM32H7 MCU
Enable printf() function to work with USB Virtual COM Port (STM32H743ZI)

__STM32CubeMX__
1. Turn on USB_OTG_FS with mode Device_Only
2. In the Middleware turn on USB_DEVICE with class Communication Device Class (Virtual Com Port)
3. Default settings
4. Generate Code

__main.c__
1. ```#include <stdio.h>```
2. Add code below between _/* USER CODE BEGIN 4 */_
```
int _write(int file, char *ptr, int len) { 
 CDC_Transmit_FS((uint8_t*) ptr, len); return len; 
}
```
For cpp project:
```
extern "C" int _write(int file, char *ptr, int len) { 
 CDC_Transmit_FS((uint8_t*) ptr, len); return len; 
}
```
That's it! 
Now you can use printf() anywere you want.

__NOTICE!__
When I started to using FreeRTOS I've noticed that printf displays an incorrect value.
Digging a bit, I found out that if you are enable the delay after CDC_Transmit_FS(), then everything works fine, so:

<details>
 <summary>using osDelay function (click to expand)</summary>
 
 
```
int _write(int file, char *ptr, int len) { 
 CDC_Transmit_FS((uint8_t*) ptr, len); 
 osDelay(1);
 return len; 
}
```
</details>

There is a better solution suggested by [Paunida](https://github.com/Paunida):

```
int _write(int file, char *ptr, int len) {
    static uint8_t rc = USBD_OK;

do {
        rc = CDC_Transmit_FS(ptr, len);
    } while (USBD_BUSY == rc);

if (USBD_FAIL == rc) {
        /// NOTE: Should never reach here.
        /// TODO: Handle this error.
        return 0;
    }
    return len;
}
```

work's for me!

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