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.