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diff --git a/docs/source/lang/serialusb.rst b/docs/source/lang/serialusb.rst index 730fb07..9beee82 100644 --- a/docs/source/lang/serialusb.rst +++ b/docs/source/lang/serialusb.rst @@ -1,8 +1,240 @@ +.. 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); + } + |