How to detect if usb connection is established

[AlexandrosAA]

Hey. I'm trying to use my H7's usb interface and i've currently set it up as a cdc device.
What i'm trying to implement though is the following. 

The stm is supposed to create a virtual connection with either a python app or a tera term terminal.

Is there a function or a variable that detects if this kind of a connection is established ? For example, the pico equivalent is tud_cdc_connected()

 What i want to build is this

while(!exampleCOnnectionVariable)
{
   HAL_DELAY(500)
}

Meaning that my stm would wait during initialization, until a connection is established and then proceed with the super loop.

[gbm]

With classic ST USB stack, you need to implement CDC_SET_CONTROL_LINE_STATE request in usbd_cdc_if.c. When ControlLineState value changes from anything different from 3 to 3, the connection is established. You may start transmitting data no sooner than 50 ms after that change.

[TDK]

Check dev_state for configured status.

if (hUsbDeviceFS.dev_state == USBD_STATE_CONFIGURED) {
    ...
}

This doesn't mean the program has the port open, just that the computer is connected. No way to detect when a program opens the serial port.

[gbm]

dev_state remains at CONFIGURED even after you disconnect the USB cable...

[FBL]

Hello @AlexandrosAA 

If I understand your request correctly, in usbd_conf.c, you can check device connection from ISR through USBD_LL_DevConnected in callback.

[AlexandrosAA]

I tried something like this

while(CDC_Transmit_HS(messageOk,sizeof(messageOk))!=USBD_OK)
{

}

but it seems that the message is transmitted, even if the port is not open. Is there a similar approach to this ? The while loop should end only if the data are accepted by my computer.

[FBL]

@AlexandrosAA When stepping in debug, and you reach this line as previously mentioned.

if (hUsbDeviceFS.dev_state == USBD_STATE_CONFIGURED) {

 You are pretty sure your host is connected.

[TDK]

If your device is bus-powered, disconnecting the cable stops the program. No problems there.

If your device is self-powered, you are required (per USB standard) to monitor VBUS and de-initialize the peripheral when VBUS drops by calling MX_USB_DEVICE_DeInit(). This will reset the state machine back to USBD_STATE_DEFAULT.

Edit: If you ignore the standard, there's probably a state variable you could check somewhere. I may look into it.