Examples: Add USB CDC example (currently only works on DK board).

examples/if_usbcdc.cpp

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2022 Micro:bit Educational Foundation and contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "mbed.h"
+#include "USBSerial.h"
+#include "USBCDC.h"
+
+// WARNING! This example currently only works with the nRF52833 DK board!
+
+/**
+ * USBSerial or USBCDC can both be used (not simultaneously) and they have
+ * the same constructor.
+ */
+// USBSerial usb_serial(
+USBCDC usb_serial (
+    false,   // connect_blocking
+    0x0d28,  // vendor_id (test value from DAPLink)
+    0x0204,  // product_id (test value from DAPLink)
+    0x0001   // product_release
+);
+
+int main(void) {
+    char msgUSB[] = "Hello from nRF52 USB CDC!\r\n";
+    DigitalOut led_orange(LED1, 0);
+    DigitalOut led_red(LED2, 0);
+
+    // Blink both LEDs to show the programme is running
+    ThisThread::sleep_for(250);
+    led_orange = 1;
+    led_red = 1;
+    ThisThread::sleep_for(250);
+    led_orange = 0;
+    led_red = 0;
+
+    // Block here and blink the red LED until the CDC port is connected
+    usb_serial.connect();
+    while (!usb_serial.ready()) {
+        ThisThread::sleep_for(250);
+        led_red = !led_red;
+    }
+    led_red = 1;
+
+    // Send a message via USB CDC and blink the orange LED
+    while (true) {
+        ThisThread::sleep_for(1000);
+        led_orange = !led_orange;
+        usb_serial.send((uint8_t *)msgUSB, strlen(msgUSB));
+        //usb_serial.printf(msgUSB); // printf only available with USBSerial constructor
+    }
+}