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+.. highlight:: cpp
+
.. _lang-serialusb:
-Serial over USB Communications
-==============================
+``SerialUSB``
+=============
+
+Used for communication between the Maple board and a computer.
+
+.. contents:: Contents
+ :local:
+
+Introduction
+------------
+
+In addition to three :ref:`serial ports <lang-serial>`, the Maple's
+STM32 microprocessor includes a dedicated USB peripheral. This
+peripheral is used to emulate a regular serial port for use as a
+terminal (text read/write). The emulated terminal is relatively slow
+and inefficient; it is best for transferring data at regular serial
+speeds (kilobaud).
+
+Library access to the emulated serial port is provided through the
+``SerialUSB`` object. You can mostly use ``SerialUSB`` as a drop-in
+replacement for ``Serial1``, ``Serial2``, and ``Serial3``.
+
+.. warning:: The ``SerialUSB`` functionality includes a 50 millisecond
+ timeout for writes, and does not try to detect if the USB host is
+ "really" connected, or just enumerated and initialized.
+
+ This means that if you have a number of calls to one of the
+ ``SerialUSB`` ``write()`` or ``print()`` functions in your code,
+ and you are not monitoring the emulated on a computer, your program
+ will run much, much slower than if it is being monitored or totally
+ disconnected (run off of a battery).
+
+ You can avoid this behavior by :ref:`deciphering the port status
+ using the DTR and RTS line status <lang-serialusb-safe-print>`; the
+ behavior of these control lines is platform dependent and we no
+ longer interpret them by default.
+
+Library Documentation
+---------------------
+
+The ``SerialUSB`` object is an instance of the ``USBSerial`` class,
+which is documented in this section. This means that you can use any
+of these functions by writing
+``SerialUSB.functionName(arguments...)``. For example, to print the
+message "hello, world!", you can write ``USBSerial.println("hello,
+world!")``.
+
+.. cpp:class:: USBSerial
+
+ Emulated serial-over-USB class. ``SerialUSB`` is the predefined
+ instance.
+
+.. cpp:function:: USBSerial::begin()
+
+ Set up the USB peripheral for emulated serial communication. The
+ peripheral is configured this way by default; calling this function
+ should only be necessary if you have disabled the peripheral using
+ ``SerialUSB.end()``.
+
+.. _lang-serialusb-end:
+
+.. cpp:function:: USBSerial::end()
+
+ Disables the USB peripheral.
+
+.. cpp:function:: unsigned int USBSerial::available()
+
+ Returns the number of bytes available for reading.
+
+.. cpp:function:: unsigned char USBSerial::read()
+
+ Returns the next available, unread character. If there are no
+ available characters (you can check this with :cpp:func:`available
+ <USBSerial::available>`), the call will block until one
+ becomes available.
+
+.. cpp:function:: USBSerial::flush()
+
+ Removes the contents of the Serial's associated input buffer. That
+ is, clears any buffered characters, so that the next character read
+ is guaranteed to be new.
+
+.. cpp:function:: USBSerial::print(unsigned char b)
+
+ Print the given byte over the USB connection.
+
+.. cpp:function:: USBSerial::print(char c)
+
+ Print the given character over the USB connection. 7-bit clean characters
+ are typically interpreted as ASCII text.
+
+.. cpp:function:: USBSerial::print(const char *str)
+
+ Print the given null-terminated string over the USB connection.
+
+.. cpp:function:: USBSerial::print(int n)
+
+ Print the argument's digits over the USB connection, in decimal format.
+ Negative values will be prefixed with a ``'-'`` character.
+
+.. cpp:function:: USBSerial::print(unsigned int n)
+
+ Print the argument's digits over the USB connection, in decimal format.
+
+.. cpp:function:: USBSerial::print(long n)
+
+ Print the argument's digits over the USB connection, in decimal
+ format. Negative values will be prefixed with a ``'-'`` character.
+
+.. cpp:function:: USBSerial::print(unsigned long n)
+
+ Print the argument's digits over the USB connection, in decimal
+ format.
+
+.. cpp:function:: USBSerial::print(long n, int base)
+
+ Print the digits of ``n`` over the USB connection, in base ``base``
+ (which may be between 2 and 16). The ``base`` value 2 corresponds
+ to binary, 8 to octal, 10 to decimal, and 16 to hexadecimal.
+ Negative values will be prefixed with a ``'-'`` character.
+
+.. cpp:function:: USBSerial::print(double n)
+
+ Print ``n``, accurate to 2 digits after the decimal point.
.. _lang-serialusb-println:
-Stub.
+.. cpp:function:: USBSerial::println(char c)
+
+ Like ``print(c)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(const char *c)
+
+ Like ``print(c)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(unsigned char b)
+
+ Like ``print(b)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(int n)
+
+ Like ``print(n)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(unsigned int n)
+
+ Like ``print(n)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(long n)
+
+ Like ``print(n)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(unsigned long n)
+
+ Like ``print(n)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(long n, int base)
+
+ Like ``print(n, b)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println(double n)
+
+ Like ``print(n)``, followed by ``"\r\n"``.
+
+.. cpp:function:: USBSerial::println()
+
+ Prints ``"\r\n"`` over the USB connection.
+
+.. cpp:function:: USBSerial::write(unsigned char ch)
+
+ Sends one character over the USB connection. This function is
+ currently blocking, although nonblocking writes are a planned
+ future extension.
+
+ This is a low-level function. One of the ``print()`` or
+ ``println()`` functions is likely to be more useful when printing
+ multiple characters, when formatting numbers for printing, etc.
+
+.. cpp:function:: USBSerial::write(const char* str)
+
+ Send the given null-terminated character string over the USB
+ connection.
+
+ This is a low-level function. One of the ``print()`` or
+ ``println()`` functions is likely to be more useful when printing
+ multiple characters, when formatting numbers for printing, etc.
+
+.. cpp:function:: USBSerial::write(void *buf, unsigned int size)
+
+ Writes the first ``size`` bytes of ``buf`` over the USB connection.
+ Each byte is transmitted as an individual character.
+
+ This is a low-level function. One of the ``print()`` or
+ ``println()`` functions is likely to be more useful when printing
+ multiple characters, when formatting numbers for printing, etc.
+
+Examples
+--------
+
+.. _lang-serialusb-safe-print:
+
+**Safe print**: This function should run smoothly and not block; the
+LED should blink at roughly the same speed whether being monitored,
+running from battery, or connected but not monitored. You may need to
+experiment with the DTR/RTS logic for your platform and device
+configuration. ::
+
+ #define LED_PIN 13
+
+ void setup() {
+ /* Set up the LED to blink */
+ pinMode(LED_PIN, OUTPUT);
+ }
+
+ void loop() {
+ // LED will stay off if we are disconnected;
+ // will blink quickly if USB is unplugged (battery etc)
+ if(SerialUSB.isConnected()) {
+ digitalWrite(LED_PIN, 1);
+ }
+ delay(100);
+
+ // If this logic fails to detect if bytes are going to
+ // be read by the USB host, then the println() will fully
+ // many times, causing a very slow LED blink.
+ // If the characters are printed and read, the blink will
+ // only slow a small amount when "really" connected, and fast
+ // when the virtual port is only configured.
+ if(SerialUSB.isConnected() && (SerialUSB.getDTR() || SerialUSB.getRTS())) {
+ for(int i=0; i<10; i++) {
+ SerialUSB.println(123456,BIN);
+ }
+ }
+ digitalWrite(LED_PIN, 0);
+ delay(100);
+ }
+