stm32/usbd_cdc_interface: Handle disconnect IRQ to set VCP disconnected.

pyb.USB_VCP().isconnected() will now return False if the USB is
disconnected after having previously been connected.

See issue #4210.

ports/stm32/usbd_cdc_interface.c

@@ -81,6 +81,11 @@ uint8_t *usbd_cdc_init(usbd_cdc_state_t *cdc_in) {
     return cdc->rx_packet_buf;
 }
 
+void usbd_cdc_deinit(usbd_cdc_state_t *cdc_in) {
+    usbd_cdc_itf_t *cdc = (usbd_cdc_itf_t*)cdc_in;
+    cdc->dev_is_connected = 0;
+}
+
 // Manage the CDC class requests
 // cmd: command code
 // pbuf: buffer containing command data (request parameters)

ports/stm32/usbdev/class/inc/usbd_cdc_msc_hid.h

@@ -185,6 +185,7 @@ uint8_t USBD_HID_ClearNAK(usbd_hid_state_t *usbd);
 
 // These are provided externally to implement the CDC interface
 uint8_t *usbd_cdc_init(usbd_cdc_state_t *cdc);
+void usbd_cdc_deinit(usbd_cdc_state_t *cdc);
 int8_t usbd_cdc_control(usbd_cdc_state_t *cdc, uint8_t cmd, uint8_t* pbuf, uint16_t length);
 int8_t usbd_cdc_receive(usbd_cdc_state_t *cdc, size_t len);
 

ports/stm32/usbdev/class/src/usbd_cdc_msc_hid.c

@@ -820,6 +820,8 @@ static uint8_t USBD_CDC_MSC_HID_DeInit(USBD_HandleTypeDef *pdev, uint8_t cfgidx)
     if ((usbd->usbd_mode & USBD_MODE_CDC) && usbd->cdc) {
         // CDC VCP component
 
+        usbd_cdc_deinit(usbd->cdc);
+
         // close endpoints
         USBD_LL_CloseEP(pdev, CDC_IN_EP);
         USBD_LL_CloseEP(pdev, CDC_OUT_EP);
@@ -830,6 +832,8 @@ static uint8_t USBD_CDC_MSC_HID_DeInit(USBD_HandleTypeDef *pdev, uint8_t cfgidx)
     if ((usbd->usbd_mode & USBD_MODE_CDC2) && usbd->cdc2) {
         // CDC VCP #2 component
 
+        usbd_cdc_deinit(usbd->cdc2);
+
         // close endpoints
         USBD_LL_CloseEP(pdev, CDC2_IN_EP);
         USBD_LL_CloseEP(pdev, CDC2_OUT_EP);