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112 lines
4.3 KiB
112 lines
4.3 KiB
/*
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* Copyright (C) 2013,2014 by Jonathan Naylor G4KLX
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* CModem is the abstract base class for all hardware modem drivers
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* (DVAP, MMDVM, DVMega, GMSK USB, etc.).
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*
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* Threading model
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* ---------------
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* Each concrete driver runs its own I/O thread (started by start(), stopped by
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* stop()). That thread reads received frames from the hardware and pushes them
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* into the m_rxData ring buffer. The repeater thread then calls read() /
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* readHeader() / readData() to drain the buffer. The mutex guards the ring
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* buffer against concurrent access between the two threads.
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*
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* Read protocol
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* -------------
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* The repeater thread calls read() each tick. If a message is available,
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* read() returns the DSMT_TYPE tag and latches the payload into an internal
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* scratch buffer. The caller then calls the matching accessor:
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* - DSMTT_HEADER -> readHeader() (returns a heap-allocated CHeaderData)
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* - DSMTT_DATA -> readData() (copies bytes into the caller's buffer)
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* Other types (START, EOT, LOST) carry no payload and need no further call.
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*/
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#ifndef Modem_H
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#define Modem_H
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#include "HeaderData.h"
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#include "RingBuffer.h"
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#include "StdCompat.h"
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#include <atomic>
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#include <thread>
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#include <mutex>
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// Message type tags pushed by the driver thread into the ring buffer.
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// Each message is prefixed with [type:1][length:1][payload:length] bytes.
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enum DSMT_TYPE {
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DSMTT_NONE, // No message waiting
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DSMTT_START, // Hardware has started (carrier / sync detected)
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DSMTT_HEADER, // A valid D-Star header has been decoded from the air
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DSMTT_DATA, // One DV frame of voice + slow-data payload
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DSMTT_EOT, // End-of-transmission detected on air
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DSMTT_LOST, // Signal lost mid-frame (carrier dropped unexpectedly)
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};
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class CModem {
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public:
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CModem();
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virtual ~CModem();
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// Start the driver I/O thread and open the hardware device.
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virtual bool start() = 0;
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// Transmit a D-Star header (called before the first writeData()).
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virtual bool writeHeader(const CHeaderData& header) = 0;
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// Transmit one DV frame; set end=true for the final frame of a transmission.
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virtual bool writeData(const unsigned char* data, unsigned int length, bool end) = 0;
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// Number of DV frames the TX buffer can still accept.
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virtual unsigned int getSpace() = 0;
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// True when the hardware is ready to accept TX frames.
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virtual bool isTXReady() = 0;
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// True while the hardware is actively transmitting.
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virtual bool isTX();
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// Drain the next message from the ring buffer; returns its type tag.
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// Must be called before readHeader() or readData().
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virtual DSMT_TYPE read();
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// Returns the header decoded by the most recent read() == DSMTT_HEADER call.
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// Caller owns the returned object.
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virtual CHeaderData* readHeader();
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// Copies DV frame bytes from the most recent read() == DSMTT_DATA call.
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virtual unsigned int readData(unsigned char* data, unsigned int length);
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// Signal the driver thread to exit and wait for it to join.
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virtual void stop();
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protected:
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// SPSC ring buffer: driver thread writes, repeater thread reads.
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CRingBuffer<unsigned char> m_rxData;
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// Guards m_rxData against concurrent access.
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std::mutex m_mutex;
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std::atomic<bool> m_tx; // Current TX state of the hardware
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std::atomic<bool> m_stopped; // Set by stop() to terminate the thread
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std::thread m_thread; // The driver I/O thread
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private:
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// Scratch state populated by read() and consumed by readHeader()/readData().
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DSMT_TYPE m_readType;
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unsigned int m_readLength;
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unsigned char* m_readBuffer;
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};
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#endif
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