STM32H7使用USB获取设备描述符失败如何解决？

使用开发板：STM32H743IITX

1，通过CUBEMX开启USB_OTG_FS，选择device_only，开启USB ON THE GO GLOBAL interrupt

2，USB时钟选择48M内部晶振

3，修改board目录下的kconfig
config BSP_USING_USBD_FS bool "Enable OTGFS as USB device" select RT_USING_USB_DEVICE default n

4，copy CUBEMX生成的时钟初始化函数覆盖掉原来的board.c

5，在ENV板级驱动目录下开启前面kconfig添加的USB，并打开USB设备框架的虚拟串口

6，重新生成工程编译

7，修改main 函数

int main(void)
{
int count = 1;
rt_device_t dev = RT_NULL;
char buf[] = “hello rt-thread!
“;

/* set LED0 pin mode to output */
rt_pin_mode(LED0_PIN, PIN_MODE_OUTPUT);
dev = rt_device_find("vcom");
if (dev)
rt_device_open(dev, RT_DEVICE_FLAG_RDWR);
else
return -RT_ERROR;
while (count++)
{
rt_pin_write(LED0_PIN, PIN_HIGH);
rt_thread_mdelay(500);
rt_device_write(dev, 0, buf, rt_strlen(buf));
rt_pin_write(LED0_PIN, PIN_LOW);
rt_thread_mdelay(500);
}
return RT_EOK;
}```

8，下载程序，电脑端显示无法识别``` \ | /

RT - Thread Operating System
/ | \ 4.0.2 build Jul 10 2019
2006 - 2019 Copyright by rt-thread team
msh >list_device
device type ref count
vcom Character Device 1
usbd USB Slave Device 0
uart1 Character Device 2
pin Miscellaneous Device 0
msh >
msh >```