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  * Authors: Andreas Sandberg
  38  */
  39
  40 #ifndef __DEV_SERIAL_HH__
  41 #define __DEV_SERIAL_HH__
  42
  43 #include "base/callback.hh"
  44 #include "sim/sim_object.hh"
  45
  46 struct SerialDeviceParams;
  47 struct SerialNullDeviceParams;
  48
  49 /**
  50  * Base class for serial devices such as terminals.
  51  *
  52  * This class provides a unified interface that all serial (RS232 or
  53  * similar) devices must implement. A device can be wired to exactly
  54  * one host serial interface (serial port model).
  55  *
  56  * SerialDevices are passive devices that are <i>driven</i> by the
  57  * serial interface using the writeData(c) (the interface sends a
  58  * character) and readData() (the interface reads a character)
  59  * methods. Serial devices need to override these methods to
  60  * communicate with the host interface layer.
  61  *
  62  * To implement basic flow control, serial devices must implement the
  63  * dataAvailable() method. This method returns true if a valid
  64  * character can be read using the readData() method. When data
  65  * becomes available, the serial device must call the
  66  * notifyInterface() method to send a callback to the interface layer.
  67  *
  68  * To send a character (host to device), the interface layer calls
  69  * writeData(char) to send a character to the serial device.
  70  *
  71  * To read a character (device to host), the interface layer calls
  72  * dataAvailable() to determine if there is a character pending. If
  73  * there is data available, it immediately calls readData() to get the
  74  * character. The receive loop in the serial device typically looks
  75  * like this:
  76  *
  77  * \code{.cc}
  78  * while (device.dataAvailable()) {
  79  *    printf("%c", (int)device.readData());
  80  * }
  81  * \endcode
  82  *
  83  * To avoid polling, the interface layer may register a data available
  84  * callback using the regInterfaceCallback() method. The device uses
  85  * this callback to notify the interface layer whenever there is new
  86  * data pending. Note that devices will normally only notify the
  87  * interface layer when there is a state transition in the
  88  * device. E.g., the dataAvailable() transitions from false to
  89  * true. This means that there can be multiple pending characters when
  90  * the interface layer receives the callback.
  91  */
  92 class SerialDevice : public SimObject
  93 {
  94   public:
  95     SerialDevice(const SerialDeviceParams *p);
  96     ~SerialDevice();
  97
  98   public: // Serial device API (UART->Device)
  99     /**
 100      * Register a data available callback into the host interface layer.
 101      *
 102      * Serial devices need to call the underlying host interface layer
 103      * to inform it of state change such as pending data that can be
 104      * read from the device by the interface layer using the readData()
 105      * method. The interface layer may use this method to register a
 106      * callback that informs it of pending data.
 107      *
 108      * @param c Callback instance from interface layer.
 109      */
 110     void regInterfaceCallback(Callback *c);
 111
 112     /**
 113      * Check if there is pending data from the serial device.
 114      *
 115      * @return true if there is data pending that can be read using
 116      * the readData() method.
 117      */
 118     virtual bool dataAvailable() const = 0;
 119
 120     /**
 121      * Transmit a character from the host interface to the device.
 122      *
 123      * @param c Received data.
 124      */
 125     virtual void writeData(uint8_t c) = 0;
 126
 127     /**
 128      * Read a character from the device.
 129      *
 130      * @return Character from the device's output buffer, undefined if
 131      * no data is pending.
 132      */
 133     virtual uint8_t readData() = 0;
 134
 135   protected:
 136     /** Notify the host interface of pending data. */
 137     void notifyInterface();
 138
 139   private:
 140     /** Currently regisxtered host interface layer callback */
 141     Callback *interfaceCallback;
 142 };
 143
 144 /**
 145  * Dummy serial device that discards all data sent to it.
 146  */
 147 class SerialNullDevice : public SerialDevice
 148 {
 149   public:
 150     SerialNullDevice(const SerialNullDeviceParams *p);
 151
 152   public:
 153     bool dataAvailable() const override { return false; }
 154     void writeData(uint8_t c) override {};
 155     uint8_t readData() override;
 156 };
 157
 158 #endif // __DEV_SERIAL_HH__