RH_ASK.h

// RH_ASK.h
//
// Copyright (C) 2014 Mike McCauley
// $Id: RH_ASK.h,v 1.17 2017/03/04 00:59:41 mikem Exp $

#ifndef RH_ASK_h
#define RH_ASK_h

#include <RHGenericDriver.h>

// Maximum message length (including the headers, byte count and FCS) we are willing to support
// This is pretty arbitrary
#define RH_ASK_MAX_PAYLOAD_LEN 67

// The length of the headers we add (To, From, Id, Flags)
// The headers are inside the payload and are therefore protected by the FCS
#define RH_ASK_HEADER_LEN 4

// This is the maximum message length that can be supported by this library. 
// Can be pre-defined to a smaller size (to save SRAM) prior to including this header
// Here we allow for 1 byte message length, 4 bytes headers, user data and 2 bytes of FCS
#ifndef RH_ASK_MAX_MESSAGE_LEN
 #define RH_ASK_MAX_MESSAGE_LEN (RH_ASK_MAX_PAYLOAD_LEN - RH_ASK_HEADER_LEN - 3)
#endif

#if !defined(RH_ASK_RX_SAMPLES_PER_BIT)
/// Number of samples per bit
 #define RH_ASK_RX_SAMPLES_PER_BIT 8
#endif //RH_ASK_RX_SAMPLES_PER_BIT  

/// The size of the receiver ramp. Ramp wraps modulo this number
#define RH_ASK_RX_RAMP_LEN 160

// Ramp adjustment parameters
// Standard is if a transition occurs before RH_ASK_RAMP_TRANSITION (80) in the ramp,
// the ramp is retarded by adding RH_ASK_RAMP_INC_RETARD (11)
// else by adding RH_ASK_RAMP_INC_ADVANCE (29)
// If there is no transition it is adjusted by RH_ASK_RAMP_INC (20)
/// Internal ramp adjustment parameter
#define RH_ASK_RAMP_INC (RH_ASK_RX_RAMP_LEN/RH_ASK_RX_SAMPLES_PER_BIT)
/// Internal ramp adjustment parameter
#define RH_ASK_RAMP_TRANSITION RH_ASK_RX_RAMP_LEN/2
/// Internal ramp adjustment parameter
#define RH_ASK_RAMP_ADJUST 9
/// Internal ramp adjustment parameter
#define RH_ASK_RAMP_INC_RETARD (RH_ASK_RAMP_INC-RH_ASK_RAMP_ADJUST)
/// Internal ramp adjustment parameter
#define RH_ASK_RAMP_INC_ADVANCE (RH_ASK_RAMP_INC+RH_ASK_RAMP_ADJUST)

/// Outgoing message bits grouped as 6-bit words
/// 36 alternating 1/0 bits, followed by 12 bits of start symbol (together called the preamble)
/// Followed immediately by the 4-6 bit encoded byte count, 
/// message buffer and 2 byte FCS
/// Each byte from the byte count on is translated into 2x6-bit words
/// Caution, each symbol is transmitted LSBit first, 
/// but each byte is transmitted high nybble first
/// This is the number of 6 bit nibbles in the preamble
#define RH_ASK_PREAMBLE_LEN 8

/////////////////////////////////////////////////////////////////////
/// \class RH_ASK RH_ASK.h <RH_ASK.h>
/// \brief Driver to send and receive unaddressed, unreliable datagrams via inexpensive ASK (Amplitude Shift Keying) or 
/// OOK (On Off Keying) RF transceivers.
///
/// The message format and software technology is based on our earlier VirtualWire library 
/// (http://www.airspayce.com/mikem/arduino/VirtualWire), with which it is compatible.
/// See http://www.airspayce.com/mikem/arduino/VirtualWire.pdf for more details. 
/// VirtualWire is now obsolete and unsupported and is replaced by this library.
///
/// RH_ASK is a Driver for Arduino, Maple and others that provides features to send short
/// messages, without addressing, retransmit or acknowledgment, a bit like UDP
/// over wireless, using ASK (amplitude shift keying). Supports a number of
/// inexpensive radio transmitters and receivers. All that is required is
/// transmit data, receive data and (for transmitters, optionally) a PTT
/// transmitter enable. Can also be used over various analog connections (not just a data radio), 
/// such as the audio channel of an A/V sender, or long TTL lines.
///
/// It is intended to be compatible with the RF Monolithics (www.rfm.com)
/// Virtual Wire protocol, but this has not been tested.
///
/// Does not use the Arduino UART. Messages are sent with a training preamble,
/// message length and checksum. Messages are sent with 4-to-6 bit encoding
/// for good DC balance, and a CRC checksum for message integrity.
///
/// But why not just use a UART connected directly to the
/// transmitter/receiver? As discussed in the RFM documentation, ASK receivers
/// require a burst of training pulses to synchronize the transmitter and
/// receiver, and also requires good balance between 0s and 1s in the message
/// stream in order to maintain the DC balance of the message. UARTs do not
/// provide these. They work a bit with ASK wireless, but not as well as this
/// code.
///
/// \par Theory of operation
///
/// See ASH Transceiver Software Designer's Guide of 2002.08.07
///   http://wireless.murata.com/media/products/apnotes/tr_swg05.pdf?ref=rfm.com
///
/// http://web.engr.oregonstate.edu/~moon/research/files/cas2_mar_07_dpll.pdf while not directly relevant 
/// is also interesting.
///
/// \par Implementation Details
///
/// Messages of up to RH_ASK_MAX_PAYLOAD_LEN (67) bytes can be sent
/// Each message is transmitted as:
///
/// - 36 bit training preamble consisting of 0-1 bit pairs
/// - 12 bit start symbol 0xb38
/// - 1 byte of message length byte count (4 to 30), count includes byte count and FCS bytes
/// - n message bytes (uincluding 4 bytes of header), maximum n is RH_ASK_MAX_MESSAGE_LEN + 4 (64)
/// - 2 bytes FCS, sent low byte-hi byte
///
/// Everything after the start symbol is encoded 4 to 6 bits, Therefore a byte in the message
/// is encoded as 2x6 bit symbols, sent hi nybble, low nybble. Each symbol is sent LSBit
/// first. The message may consist of any binary digits.
/// 
/// The Arduino Diecimila clock rate is 16MHz => 62.5ns/cycle.
/// For an RF bit rate of 2000 bps, need 500microsec bit period.
/// The ramp requires 8 samples per bit period, so need 62.5microsec per sample => interrupt tick is 62.5microsec.
///
/// The maximum packet length consists of
/// (6 + 2 + RH_ASK_MAX_MESSAGE_LEN*2) * 6 = 768 bits = 0.384 secs (at 2000 bps).
/// where RH_ASK_MAX_MESSAGE_LEN is RH_ASK_MAX_PAYLOAD_LEN - 7 (= 60).
/// The code consists of an ISR interrupt handler. Most of the work is done in the interrupt
/// handler for both transmit and receive, but some is done from the user level. Expensive
/// functions like CRC computations are always done in the user level.
///
/// \par Supported Hardware
///
/// A range of communications
/// hardware is supported. The ones listed below are available in common retail
/// outlets in Australia and other countries for under $10 per unit. Many
/// other modules may also work with this software. 
///
/// Runs on a wide range of Arduino processors using Arduino IDE 1.0 or later.
/// Also runs on on Energia, 
/// with MSP430G2553 / G2452 and Arduino with ATMega328 (courtesy Yannick DEVOS - XV4Y), 
/// but untested by us. It also runs on Teensy 3.0 (courtesy of Paul
/// Stoffregen), but untested by us. Also compiles and runs on ATtiny85 in
/// Arduino environment, courtesy r4z0r7o3. Also compiles on maple-ide-v0.0.12,
/// and runs on Maple, flymaple 1.1 etc. Runs on ATmega8/168 (Arduino Diecimila,
/// Uno etc), ATmega328 and can run on almost any other AVR8 platform,
/// without relying on the Arduino framework, by properly configuring the
/// library editing the RH_ASK.h header file for describing the access
/// to IO pins and for setting up the timer.
/// Runs on ChipKIT Core supported processors such as Uno32 etc.
///
/// - Receivers
///  - RX-B1 (433.92MHz) (also known as ST-RX04-ASK)
///  - RFM83C from HopeRF http://www.hoperfusa.com/details.jsp?pid=126
///  - SYN480R and other similar ASK receivers
/// - Transmitters: 
///  - TX-C1 (433.92MHz)
///  - RFM85 from HopeRF http://www.hoperfusa.com/details.jsp?pid=127
///  - SYN115, F115 and other similar ASK transmitters
/// - Transceivers
///  - DR3100 (433.92MHz)
///
/// \par Connecting to Arduino
///
/// Most transmitters can be connected to Arduino like this:
/// \code
/// Arduino                         Transmitter
///  GND------------------------------GND
///  D12------------------------------Data
///  5V-------------------------------VCC
/// \endcode
///
/// Most receivers can be connected to Arduino like this:
/// \code
/// Arduino                         Receiver
///  GND------------------------------GND
///  D11------------------------------Data
///  5V-------------------------------VCC
///                                   SHUT (not connected)
///                                   WAKEB (not connected)
///                                   GND |
///                                   ANT |- connect to your antenna syetem
/// \endcode
///
/// RH_ASK works with ATTiny85, using Arduino 1.0.5 and tinycore from
/// https://code.google.com/p/arduino-tiny/downloads/detail?name=arduino-tiny-0100-0018.zip
/// Tested with the examples ask_transmitter and ask_receiver on ATTiny85.
/// Caution: The RAM memory requirements on an ATTiny85 are *very* tight. Even the bare bones
/// ask_transmitter sketch barely fits in eh RAM available on the ATTiny85. Its unlikely to work on 
/// smaller ATTinys such as the ATTiny45 etc. If you have wierd behaviour, consider
/// reducing the size of RH_ASK_MAX_PAYLOAD_LEN to the minimum you can work with.
/// Caution: the default internal clock speed on an ATTiny85 is 1MHz. You MUST set the internal clock speed
/// to 8MHz. You can do this with Arduino IDE, tineycore and ArduinoISP by setting the board type to "ATtiny85@8MHz',
/// setting theProgrammer to 'Arduino as ISP' and selecting Tools->Burn Bootloader. This does not actually burn a
/// bootloader into the tiny, it just changes the fuses so the chip runs at 8MHz. 
/// If you run the chip at 1MHz, you will get RK_ASK speeds 1/8th of the expected.
///
/// Initialise RH_ASK for ATTiny85 like this:
/// // #include <SPI.h> // comment this out, not needed
/// RH_ASK driver(2000, 4, 3); // 200bps, TX on D3 (pin 2), RX on D4 (pin 3)
/// then:
/// Connect D3 (pin 2) as the output to the transmitter
/// Connect D4 (pin 3) as the input from the receiver.
/// 
///
/// For testing purposes you can connect 2 Arduino RH_ASK instances directly, by
/// connecting pin 12 of one to 11 of the other and vice versa, like this for a duplex connection:
///
/// \code
/// Arduino 1         wires         Arduino 1
///  D11-----------------------------D12
///  D12-----------------------------D11
///  GND-----------------------------GND
/// \endcode
///
/// You can also connect 2 RH_ASK instances over a suitable analog
/// transmitter/receiver, such as the audio channel of an A/V transmitter/receiver. You may need
/// buffers at each end of the connection to convert the 0-5V digital output to a suitable analog voltage.
///
/// Measured power output from RFM85 at 5V was 18dBm.
///
/// \par ESP8266
/// This module has been tested with the ESP8266 using an ESP-12 on a breakout board 
/// ESP-12E SMD Adaptor Board with Power Regulator from tronixlabs 
/// http://tronixlabs.com.au/wireless/esp8266/esp8266-esp-12e-smd-adaptor-board-with-power-regulator-australia/
/// compiled on Arduino 1.6.5 and the ESP8266 support 2.0 installed with Board Manager.
/// CAUTION: do not use pin 11 for IO with this chip: it will cause the sketch to hang. Instead
/// use constructor arguments to configure different pins, eg:
/// \code
/// RH_ASK driver(2000, 2, 4, 5);
/// \endcode
/// Which will initialise the driver at 2000 bps, recieve on GPIO2, transmit on GPIO4, PTT on GPIO5.
/// Caution: on the tronixlabs breakout board, pins 4 and 5 may be labelled vice-versa.
///
/// \par Timers
/// The RH_ASK driver uses a timer-driven interrupt to generate 8 interrupts per bit period. RH_ASK
/// takes over a timer on Arduino-like platforms. By default it takes over Timer 1. You can force it
/// to use Timer 2 instead by enabling the define RH_ASK_ARDUINO_USE_TIMER2 near the top of RH_ASK.cpp
/// On Arduino Zero it takes over timer TC3. On Arduino Due it takes over timer
/// TC0. On ESP8266, takes over timer0 (which conflicts with ServoTimer0).
///
/// Caution: ATTiny85 has only 2 timers, one (timer 0) usually used for
/// millis() and one (timer 1) for PWM analog outputs. The RH_ASK Driver
/// library, when built for ATTiny85, takes over timer 0, which prevents use
/// of millis() etc but does permit analog outputs. This will affect the accuracy of millis() and time
/// measurement.
class RH_ASK : public RHGenericDriver
{
public:
    /// Constructor.
    /// At present only one instance of RH_ASK per sketch is supported.
    /// \param[in] speed The desired bit rate in bits per second
    /// \param[in] rxPin The pin that is used to get data from the receiver
    /// \param[in] txPin The pin that is used to send data to the transmitter
    /// \param[in] pttPin The pin that is connected to the transmitter controller. It will be set HIGH to enable the transmitter (unless pttInverted is true).
    /// \param[in] pttInverted true if you desire the pttin to be inverted so that LOW wil enable the transmitter.
    RH_ASK(uint16_t speed = 2000, uint8_t rxPin = 11, uint8_t txPin = 12, uint8_t pttPin = 10, bool pttInverted = false);

    /// Initialise the Driver transport hardware and software.
    /// Make sure the Driver is properly configured before calling init().
    /// \return true if initialisation succeeded.
    virtual bool    init();

    /// Tests whether a new message is available
    /// from the Driver. 
    /// On most drivers, this will also put the Driver into RHModeRx mode until
    /// a message is actually received bythe transport, when it wil be returned to RHModeIdle.
    /// This can be called multiple times in a timeout loop
    /// \return true if a new, complete, error-free uncollected message is available to be retreived by recv()
    virtual bool    available();

    /// Turns the receiver on if it not already on.
    /// If there is a valid message available, copy it to buf and return true
    /// else return false.
    /// If a message is copied, *len is set to the length (Caution, 0 length messages are permitted).
    /// You should be sure to call this function frequently enough to not miss any messages
    /// It is recommended that you call it in your main loop.
    /// \param[in] buf Location to copy the received message
    /// \param[in,out] len Pointer to available space in buf. Set to the actual number of octets copied.
    /// \return true if a valid message was copied to buf
    virtual bool    recv(uint8_t* buf, uint8_t* len);

    /// Waits until any previous transmit packet is finished being transmitted with waitPacketSent().
    /// Then loads a message into the transmitter and starts the transmitter. Note that a message length
    /// of 0 is NOT permitted. 
    /// \param[in] data Array of data to be sent
    /// \param[in] len Number of bytes of data to send (> 0)
    /// \return true if the message length was valid and it was correctly queued for transmit
    virtual bool    send(const uint8_t* data, uint8_t len);

    /// Returns the maximum message length 
    /// available in this Driver.
    /// \return The maximum legal message length
    virtual uint8_t maxMessageLength();

    /// If current mode is Rx or Tx changes it to Idle. If the transmitter or receiver is running, 
    /// disables them.
    void           setModeIdle();

    /// If current mode is Tx or Idle, changes it to Rx. 
    /// Starts the receiver in the RF69.
    void           setModeRx();

    /// If current mode is Rx or Idle, changes it to Rx. F
    /// Starts the transmitter in the RF69.
    void           setModeTx();

    /// dont call this it used by the interrupt handler
    void            handleTimerInterrupt();

    /// Returns the current speed in bits per second
    /// \return The current speed in bits per second
    uint16_t        speed() { return _speed;}

#if (RH_PLATFORM == RH_PLATFORM_ESP8266)
    /// ESP8266 timer0 increment value
    uint32_t _timerIncrement;
#endif

protected:
    /// Helper function for calculating timer ticks
    uint8_t         timerCalc(uint16_t speed, uint16_t max_ticks, uint16_t *nticks);

    /// Set up the timer and its interrutps so the interrupt handler is called at the right frequency
    void            timerSetup();

    /// Read the rxPin in a platform dependent way, taking into account whether it is inverted or not
    bool            readRx();

    /// Write the txPin in a platform dependent way
    void            writeTx(bool value);

    /// Write the txPin in a platform dependent way, taking into account whether it is inverted or not
    void            writePtt(bool value);

    /// Translates a 6 bit symbol to its 4 bit plaintext equivalent
    uint8_t         symbol_6to4(uint8_t symbol);

    /// The receiver handler function, called a 8 times the bit rate
    void            receiveTimer();

    /// The transmitter handler function, called a 8 times the bit rate 
    void            transmitTimer();

    /// Check whether the latest received message is complete and uncorrupted
    /// We should always check the FCS at user level, not interrupt level
    /// since it is slow
    void            validateRxBuf();

    /// Configure bit rate in bits per second
    uint16_t        _speed;

    /// The configure receiver pin
    uint8_t         _rxPin;

    /// The configure transmitter pin
    uint8_t         _txPin;

    /// The configured transmitter enable pin
    uint8_t         _pttPin;

    /// True of the sense of the rxPin is to be inverted
    bool            _rxInverted;

    /// True of the sense of the pttPin is to be inverted
    bool            _pttInverted;

    // Used in the interrupt handlers
    /// Buf is filled but not validated
    volatile bool   _rxBufFull;

    /// Buf is full and valid
    volatile bool   _rxBufValid;

    /// Last digital input from the rx data pin
    volatile bool   _rxLastSample;

    /// This is the integrate and dump integral. If there are <5 0 samples in the PLL cycle
    /// the bit is declared a 0, else a 1
    volatile uint8_t _rxIntegrator;

    /// PLL ramp, varies between 0 and RH_ASK_RX_RAMP_LEN-1 (159) over 
    /// RH_ASK_RX_SAMPLES_PER_BIT (8) samples per nominal bit time. 
    /// When the PLL is synchronised, bit transitions happen at about the
    /// 0 mark. 
    volatile uint8_t _rxPllRamp;

    /// Flag indicates if we have seen the start symbol of a new message and are
    /// in the processes of reading and decoding it
    volatile uint8_t _rxActive;

    /// Last 12 bits received, so we can look for the start symbol
    volatile uint16_t _rxBits;

    /// How many bits of message we have received. Ranges from 0 to 12
    volatile uint8_t _rxBitCount;
    
    /// The incoming message buffer
    uint8_t _rxBuf[RH_ASK_MAX_PAYLOAD_LEN];
    
    /// The incoming message expected length
    volatile uint8_t _rxCount;
    
    /// The incoming message buffer length received so far
    volatile uint8_t _rxBufLen;

    /// Index of the next symbol to send. Ranges from 0 to vw_tx_len
    uint8_t _txIndex;

    /// Bit number of next bit to send
    uint8_t _txBit;

    /// Sample number for the transmitter. Runs 0 to 7 during one bit interval
    uint8_t _txSample;

    /// The transmitter buffer in _symbols_ not data octets
    uint8_t _txBuf[(RH_ASK_MAX_PAYLOAD_LEN * 2) + RH_ASK_PREAMBLE_LEN];

    /// Number of symbols in _txBuf to be sent;
    uint8_t _txBufLen;

};

/// @example ask_reliable_datagram_client.pde
/// @example ask_reliable_datagram_server.pde
/// @example ask_transmitter.pde
/// @example ask_receiver.pde
#endif