src/dev/serial/serial.hh

   1 /*
   2  * Copyright (c) 2014, 2017 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
  18  * redistributions in binary form must reproduce the above copyright
  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  31  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  32  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  */
  37
  38 #ifndef __DEV_SERIAL_HH__
  39 #define __DEV_SERIAL_HH__
  40
  41 #include <functional>
  42
  43 #include "sim/sim_object.hh"
  44
  45 struct SerialDeviceParams;
  46 struct SerialNullDeviceParams;
  47
  48 /**
  49  * Base class for serial devices such as terminals.
  50  *
  51  * This class provides a unified interface that all serial (RS232 or
  52  * similar) devices must implement. A device can be wired to exactly
  53  * one host serial interface (serial port model).
  54  *
  55  * SerialDevices are passive devices that are <i>driven</i> by the
  56  * serial interface using the writeData(c) (the interface sends a
  57  * character) and readData() (the interface reads a character)
  58  * methods. Serial devices need to override these methods to
  59  * communicate with the host interface layer.
  60  *
  61  * To implement basic flow control, serial devices must implement the
  62  * dataAvailable() method. This method returns true if a valid
  63  * character can be read using the readData() method. When data
  64  * becomes available, the serial device must call the
  65  * notifyInterface() method to send a callback to the interface layer.
  66  *
  67  * To send a character (host to device), the interface layer calls
  68  * writeData(char) to send a character to the serial device.
  69  *
  70  * To read a character (device to host), the interface layer calls
  71  * dataAvailable() to determine if there is a character pending. If
  72  * there is data available, it immediately calls readData() to get the
  73  * character. The receive loop in the serial device typically looks
  74  * like this:
  75  *
  76  * \code{.cc}
  77  * while (device.dataAvailable()) {
  78  *    printf("%c", (int)device.readData());
  79  * }
  80  * \endcode
  81  *
  82  * To avoid polling, the interface layer may register a data available
  83  * callback using the regInterfaceCallback() method. The device uses
  84  * this callback to notify the interface layer whenever there is new
  85  * data pending. Note that devices will normally only notify the
  86  * interface layer when there is a state transition in the
  87  * device. E.g., the dataAvailable() transitions from false to
  88  * true. This means that there can be multiple pending characters when
  89  * the interface layer receives the callback.
  90  */
  91 class SerialDevice : public SimObject
  92 {
  93   public:
  94     SerialDevice(const SerialDeviceParams &p);
  95     ~SerialDevice();
  96
  97   public: // Serial device API (UART->Device)
  98     /**
  99      * Register a data available callback into the host interface layer.
 100      *
 101      * Serial devices need to call the underlying host interface layer
 102      * to inform it of state change such as pending data that can be
 103      * read from the device by the interface layer using the readData()
 104      * method. The interface layer may use this method to register a
 105      * callback that informs it of pending data.
 106      *
 107      * @param c Callback from interface layer.
 108      */
 109     void regInterfaceCallback(const std::function<void()> &callback);
 110
 111     /**
 112      * Check if there is pending data from the serial device.
 113      *
 114      * @return true if there is data pending that can be read using
 115      * the readData() method.
 116      */
 117     virtual bool dataAvailable() const = 0;
 118
 119     /**
 120      * Transmit a character from the host interface to the device.
 121      *
 122      * @param c Received data.
 123      */
 124     virtual void writeData(uint8_t c) = 0;
 125
 126     /**
 127      * Read a character from the device.
 128      *
 129      * @return Character from the device's output buffer, undefined if
 130      * no data is pending.
 131      */
 132     virtual uint8_t readData() = 0;
 133
 134   protected:
 135     /** Notify the host interface of pending data. */
 136     void notifyInterface();
 137
 138   private:
 139     /** Currently regisxtered host interface layer callback */
 140     std::function<void()> interfaceCallback;
 141 };
 142
 143 /**
 144  * Dummy serial device that discards all data sent to it.
 145  */
 146 class SerialNullDevice : public SerialDevice
 147 {
 148   public:
 149     SerialNullDevice(const SerialNullDeviceParams &p);
 150
 151   public:
 152     bool dataAvailable() const override { return false; }
 153     void writeData(uint8_t c) override {};
 154     uint8_t readData() override;
 155 };
 156
 157 #endif // __DEV_SERIAL_HH__