diff options
Diffstat (limited to 'docs/source/usb.rst')
| -rw-r--r-- | docs/source/usb.rst | 163 |
1 files changed, 8 insertions, 155 deletions
diff --git a/docs/source/usb.rst b/docs/source/usb.rst index baabde5..f502f31 100644 --- a/docs/source/usb.rst +++ b/docs/source/usb.rst @@ -6,21 +6,6 @@ USB ===== -.. note:: Changes and Caveats - - The SerialUSB functionality was modified for the 0.0.6 IDE - release. It now 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 SerialUSB writes or prints in your code and you are not - monitoring on a computer your program will run much, much slower - than if it is being monitored or totally disconnected (battery). - - You can avoid this behavior by :ref:`deciphering the port status - <usb-safe-print>` using the DTR and RTS line status; the behavior - of these control lines is platform dependent and we no longer - interpret them by default. - The Maple STM32 microprocessor includes a dedicated USB peripheral which can be configured to act as a general USB slave device with transfer rates up to 12Mbps (it unfortunately can't be configured as a @@ -30,152 +15,21 @@ and second, 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). Users -requiring faster data transfer should consider implementing a -different communications protocol; the Maple could be reprogrammed to -appear as a mass storage device (thumb drive), human interface device -(mouse or keyboard), microphone, or any other USB device. +for transferring data at regular serial speeds (kilobaud). Library +support for accessing the emulated terminal is available at the +:ref:`SerialUSB <lang-serialusb>` reference. -The SerialUSB channel is also used as part of the auto-reset feature -of the IDE to program the board (on Maple Rev3): a :ref:`magic +The SerialUSB channel is used as part of the auto-reset feature of the +IDE to program the board on Maple Rev 3 and Rev 5: a :ref:`magic sequence of control line toggles and transmitted data <bootloader-rev3>` causes the Maple to reset itself and enter bootloader mode. As an unfortunate consequence, the auto-reset will not work if the IDE can not access the serial port, either due to a conflict with another program (serial monitor) or because the interface has been disabled from the Maple side (through -``SerialUSB.end()``). - -Function Reference ------------------- - -``SerialUSB.print(...)``/\ ``SerialUSB.println(...)`` - - Writes data into the port buffer to be transmitted as soon as - possible. Accepts strings (``char*``). If a raw integer is passed - the corresponding ASCII character will be transmitted; to print - out a number in human readable form add a second parameter with - the base system. For example, to print out the decimal number - "1234", use ``SerialUSB.print(1234, DEC)``; to print out the - binary number "1001", use ``SerialUSB.print(9, BIN)``. - -.. _usb-write: - -``SerialUSB.write(bytes)`` - - ``write`` is a lower-level function that writes bytes directly - into the buffer. :ref:`print() <usb-print>` often calls this - function dozens of times to write out a single formatted number; - user code can optimize raw data speed by calling this function - with 64-byte chunks instead. - -``SerialUSB.available()``/\ ``SerialUSB.read()`` - - ``SerialUSB.read()`` will return the next available character - (``byte``) that has been received over the port. - ``SerialUSB.available()`` returns how many such bytes are actually - available. If there is no data, ``read`` will block/fail, so the - usual program structure is to poll with ``available`` and only - ``read`` if there are data to read. - -``SerialUSB.read(buffer, length)`` - - An alternative version of ``SerialUSB.read``; will write the next - ``length`` available characters into the array ``buffer``. - -``SerialUSB.pending()`` - - Returns the number of bytes waiting in the transmit - buffer. Usercode can use this to prevent any blocking/waiting when - using the direct :ref:`write <usb-write>` functions, or to check - if data was actually requested/received by the host. - -``SerialUSB.getRTS()`` - - Returns the state (1 or 0) of the virtual RTS ("ready to send") - line. This can be used to guess if the USB host is actively - waiting for data (e.g., if a serial monitor program is running) or - just "configured" (i.e., the virtual serial port is configured, - but no program is reading data). - -``SerialUSB.getDTR()`` - - Returns the state (1 or 0) of the virtual DTR ("data terminal - ready") line. This can be used to guess if the USB host is - actively waiting for data (e.g., if a serial monitor program is - running) or just "configured" (i.e., the virtual serial port is - configured, but no program is reading data). - -.. TODO deprecate crap out of above two functions; write a sane API - -``SerialUSB.isConnected()`` - - Returns 1 if the USB host is connected and the virtual serial - interface is initialized (though not necessarily active). - Otherwise, returns 0. - -``SerialUSB.end()``/\ ``SerialUSB.begin()`` - - The USB peripheral is enabled by default so that the auto-reset - feature will work, but it can be disabled/restarted at any time - with the ``SerialUSB.end()`` and ``SerialUSB.begin()`` - functions. - - ``SerialUSB.end()`` is a relatively hard shutdown, similar to - unplugging the board; this may crash or confuse any programs - running host-side. Note that calling this function will require - the Maple to be put into :ref:`perpetual bootloader mode - <troubleshooting-perpetual-bootloader>` before another program can - be uploaded onto it, unless ``SerialUSB.begin()`` is called before - the upload is attempted. - - It's probably wise to wait a few seconds between calls to - ``SerialUSB.end()`` and ``SerialUSB.begin()`` (or to - ``SerialUSB.begin()`` and ``SerialUSB.print()``) to let the - computer reconfigure. - -Code Examples -------------- - -.. _usb-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); - } +:ref:`SerialUSB.end() <lang-serialusb-end>`). A solution to the +second problem is the use of :ref:`perpetual bootloader mode +<troubleshooting-perpetual-bootloader>`. Recommended Reading ------------------- @@ -185,7 +39,6 @@ Recommended Reading * Linux Kernel documentation for `USB ACM <http://www.kernel.org/doc/Documentation/usb/acm.txt>`_ and `USB Serial <http://www.kernel.org/doc/Documentation/usb/usb-serial.txt>`_ * STMicro documentation for STM32F103RB microcontroller: - * `All documents <http://www.st.com/mcu/devicedocs-STM32F103RB-110.html>`_ * `Datasheet <http://www.st.com/stonline/products/literature/ds/13587.pdf>`_ (pdf) * `Reference Manual <http://www.st.com/stonline/products/literature/rm/13902.pdf>`_ (pdf) * `Programming Manual <http://www.st.com/stonline/products/literature/pm/15491.pdf>`_ (pdf; assembly |