support dropping Serial, add no_serial example

Author: hathach

examples/CDC/no_serial/no_serial.ino

@@ -0,0 +1,36 @@
+/*********************************************************************
+ Adafruit invests time and resources providing this open source code,
+ please support Adafruit and open-source hardware by purchasing
+ products from Adafruit!
+
+ MIT license, check LICENSE for more information
+ Copyright (c) 2019 Ha Thach for Adafruit Industries
+ All text above, and the splash screen below must be included in
+ any redistribution
+*********************************************************************/
+
+#include "Adafruit_TinyUSB.h"
+
+/* This sketch demonstrates USB CDC Serial can be dropped by simply
+ * call Serial.end() within setup(). This must be called before any
+ * other USB interfaces (MSC / HID) begin to have a clean configuration
+ *
+ * Note: this will cause device to loose the touch1200 and require
+ * user manual interaction to put device into bootloader/DFU mode.
+ */
+
+int led = LED_BUILTIN;
+
+void setup()
+{
+  Serial.end();
+  pinMode(led, OUTPUT);
+}
+
+void loop()
+{
+  digitalWrite(led, HIGH);
+  delay(1000);
+  digitalWrite(led, LOW);
+  delay(1000);
+}

src/arduino/Adafruit_USBD_CDC.cpp

@@ -77,7 +77,7 @@ void Adafruit_USBD_CDC::begin (uint32_t baud, uint8_t config)
 
 void Adafruit_USBD_CDC::end(void)
 {
-  // nothing to do
+  USBDevice.clearConfiguration();
 }
 
 uint32_t Adafruit_USBD_CDC::baud(void)

src/arduino/Adafruit_USBD_Device.cpp

@@ -70,8 +70,8 @@ void Adafruit_USBD_Device::clearConfiguration(void)
     .bDeviceSubClass    = 0,
     .bDeviceProtocol    = 0,
     .bMaxPacketSize0    = CFG_TUD_ENDPOINT0_SIZE,
-    .idVendor           = 0,
-    .idProduct          = 0,
+    .idVendor           = USB_VID,
+    .idProduct          = USB_PID,
     .bcdDevice          = 0x0100,
     .iManufacturer      = STRID_MANUFACTURER,
     .iProduct           = STRID_PRODUCT,
@@ -225,7 +225,6 @@ uint8_t Adafruit_USBD_Device::getSerialDescriptor(uint16_t* serial_utf16)
 bool Adafruit_USBD_Device::begin(uint8_t rhport)
 {
   clearConfiguration();
-  setID(USB_VID, USB_PID);
 
   // Serial is always added by default
   // Use Interface Association Descriptor (IAD) for CDC