H743ZI-Nucleo USB-OTG-FS cofigured as virtual com port, usb speed is too low

[esukh]

I want to make a streaming from MCU to PC over USB and write as a binary file. Now I have some real problems with USB speed. I tried to measure it and

while (1)
  {
    /* USER CODE END WHILE */
    /* USER CODE BEGIN 3 */
    
    if ((dmaFlag != 0)) {
      for(int i = 0; i < DMA_BUFFER_SIZE/4096; ++i) {
        CDC_Transmit_FS(buffer + 4096*i, 4096*sizeof(unsigned int));
        while(strcmp(string, "copy") != 0);
        string[0] = 0;
        //printf("roger\r\n");
      }
      
      //printArray();
      CDC_Transmit_FS(endstring, strlen(endstring));
      dmaFlag = 0;
    }
    
  }

where

#define DMA_BUFFER_SIZE   65536

and PC listener code

#include <windows.h>
#include <stdio.h>
#include <stdint.h>
 
int64_t GlobalCounterFrequency;
 
inline float Win32GetSecondsElapsed(LARGE_INTEGER Start, LARGE_INTEGER End)
{
  float Result = (float)(End.QuadPart - Start.QuadPart) /
    (float)GlobalCounterFrequency;
  return(Result);
}
 
LARGE_INTEGER startCounter, endCounter;
float time = 0;
 
int main()
{
  // Define the five bytes to send ("hello")
  char* bytes_to_send = "send_data";
  
  // Declare variables and structures
  HANDLE hSerial;
  DCB dcbSerialParams = {0};
  COMMTIMEOUTS timeouts = {0};
  
  // Open the highest available serial port number
  fprintf(stderr, "Opening serial port...");
  hSerial = CreateFile(
    "\\\\.\\COM6", GENERIC_READ|GENERIC_WRITE, 0, NULL,
    OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );
  if (hSerial == INVALID_HANDLE_VALUE)
  {
    fprintf(stderr, "Error\n");
    return 1;
  }
  else fprintf(stderr, "OK\n");
  
  //SetupComm(hSerial, 1200, 1200);
  
  // Set device parameters (38400 baud, 1 start bit,
  // 1 stop bit, no parity)
  dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
  if (GetCommState(hSerial, &dcbSerialParams) == 0)
  {
    fprintf(stderr, "Error getting device state\n");
    CloseHandle(hSerial);
    return 1;
  }
  /*
  dcbSerialParams.BaudRate = CBR_38400;
  dcbSerialParams.ByteSize = 8;
  dcbSerialParams.StopBits = ONESTOPBIT;
  dcbSerialParams.Parity = NOPARITY;
  if(SetCommState(hSerial, &dcbSerialParams) == 0)
  {
    fprintf(stderr, "Error setting device parameters\n");
    DWORD lastError = GetLastError();
    CloseHandle(hSerial);
    return 1;
  }
  */
  // Set COM port timeout settings
  timeouts.ReadIntervalTimeout = 50;
  timeouts.ReadTotalTimeoutConstant = 50;
  timeouts.ReadTotalTimeoutMultiplier = 10;
  timeouts.WriteTotalTimeoutConstant = 50;
  timeouts.WriteTotalTimeoutMultiplier = 10;
  if(SetCommTimeouts(hSerial, &timeouts) == 0)
  {
    fprintf(stderr, "Error setting timeouts\n");
    CloseHandle(hSerial);
    return 1;
  }
  
  // Send specified text (remaining command line arguments)
#if 1
  DWORD bytes_written, total_bytes_written = 0;
  fprintf(stderr, "Sending bytes...");
  if(!WriteFile(hSerial, bytes_to_send, strlen(bytes_to_send), &bytes_written, NULL))
  {
    fprintf(stderr, "Error\n");
    CloseHandle(hSerial);
    return 1;
  }   
  fprintf(stderr, "%d bytes written\n", bytes_written);
#endif
  char *Filename = "orbita_data.bin";
  
  // this should always create new file data be written into
  HANDLE FileHandle = CreateFile(Filename, GENERIC_WRITE, 0, 0,
                                 CREATE_ALWAYS, 0, 0);
  if(FileHandle != INVALID_HANDLE_VALUE) {
    // NOTE(Egor): succeed
  }
  else {
    // NOTE(Egor); fail
  }
  
  LARGE_INTEGER CounterFrequencyResult;
  QueryPerformanceFrequency(&CounterFrequencyResult);
  GlobalCounterFrequency = CounterFrequencyResult.QuadPart;
  
  QueryPerformanceCounter(&startCounter);  
  for(;;) {
    
#define number_of_ccr 4096
    unsigned int lpBuffer[number_of_ccr] = {0};
    unsigned long nNumberOfBytesToRead = number_of_ccr*4;
    unsigned long lpNumberOfBytesRead;
    
 
    
    ReadFile(
      hSerial,
      lpBuffer,
      nNumberOfBytesToRead,
      &lpNumberOfBytesRead,
      NULL
      );
    
    if(!strcmp(lpBuffer, "end\r\n")) {
      CloseHandle(FileHandle);
      fprintf(stderr, "end flag was received\n");
      break;
    }
    else if(lpNumberOfBytesRead > 0) {
      // NOTE(Egor): succeed
      char *copyString = "copy";
      WriteFile(hSerial, copyString , strlen(copyString), &bytes_written, NULL);
      DWORD BytesWritten;
      // write data to file
      WriteFile(FileHandle, lpBuffer, nNumberOfBytesToRead, &BytesWritten, 0);
    }
    
  }
  
 
  QueryPerformanceCounter(&endCounter);
  time = Win32GetSecondsElapsed(startCounter, endCounter);
  char DebugBuffer[256];
  sprintf(DebugBuffer, "time: %f \n", time);
  OutputDebugStringA(DebugBuffer);
  
  // Close serial port
  fprintf(stderr, "Closing serial port...");
  if (CloseHandle(hSerial) == 0)
  {
    fprintf(stderr, "Error\n");
    return 1;
  }
  fprintf(stderr, "OK\n");
  
  // exit normally
  return 0;
}

give me no more that 256kb over 2.5(!!!) seconds if QPC doesn't lying to me.

Is something ridiculously wrong with my setup? Or it's a common speed for USB-OTG-FS configured as virtual com port? Could someone provide an exmaple or advice about USB streaming?

Thanks in advance, any help will be highly apreciated, actully I run out of ideas already.