VirtualWire.h

// VirtualWire.h
//
// Virtual Wire implementation for Arduino
// See the README file in this directory fdor documentation
// 
// Author: Mike McCauley (mikem@open.com.au)
// Copyright (C) 2008 Mike McCauley
// $Id: VirtualWire.h,v 1.3 2009/03/30 00:07:24 mikem Exp $

#ifndef VirtualWire_h
#define VirtualWire_h

#include <stdlib.h>
#include <wiring.h>

// Maximum number of bytes in a message, counting the byte count and FCS
#define VW_MAX_MESSAGE_LEN 30

// The maximum payload length
#define VW_MAX_PAYLOAD VW_MAX_MESSAGE_LEN-3

// The size of the receiver ramp. Ramp wraps modulu this number
#define VW_RX_RAMP_LEN 160

// Number of samples per bit
#define VW_RX_SAMPLES_PER_BIT 8

// Ramp adjustment parameters
// Standard is if a transition occurs before VW_RAMP_TRANSITION (80) in the ramp,
// the ramp is retarded by adding VW_RAMP_INC_RETARD (11)
// else by adding VW_RAMP_INC_ADVANCE (29)
// If there is no transition it is adjusted by VW_RAMP_INC (20)
#define VW_RAMP_INC (VW_RX_RAMP_LEN/VW_RX_SAMPLES_PER_BIT)
#define VW_RAMP_TRANSITION VW_RX_RAMP_LEN/2
#define VW_RAMP_ADJUST 9
#define VW_RAMP_INC_RETARD (VW_RAMP_INC-VW_RAMP_ADJUST)
#define VW_RAMP_INC_ADVANCE (VW_RAMP_INC+VW_RAMP_ADJUST)

// Outgoing message bits grouped as 6-bit words
// 36 alternating 1/0 bits, followed by 12 bits of start symbol
// 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
#define VW_HEADER_LEN 8

// Cant really do this as a real C++ class, since we need to have 
// an ISR
extern "C"
{
    // Set the digital IO pin to be for transmit data
    // Defaults to 12
    extern void vw_set_tx_pin(uint8_t pin);

    // Set the digital IO pin to be for receive data
    // Defaults to 11
    extern void vw_set_rx_pin(uint8_t pin);

    // Set the digital IO pin to enable the transmitter (press to talk)
    // Defaults to 10
    extern void vw_set_ptt_pin(uint8_t pin);

    // By default the PTT pin goes high when the transmitter is enabled.
    // This flag forces it low when the transmitter is enabled.
    extern void vw_set_ptt_inverted(uint8_t inverted);

    // Initialise the VirtualWire software, to operate at speed bits per second
    // Call this one in your setup() after any vw_set_* calls
    // Must call vw_rx_start() before you will get any messages
    extern void vw_setup(uint16_t speed);

    // Start the Phase Locked Loop listening to the receiver
    // Must do this before you can receive any messages
    // When a message is available (good checksum or not), vw_have_message();
    // will return true.
    extern void vw_rx_start();

    // Stop the Phase Locked Loop listening to the receiver
    // No messages will be received until vw_rx_start() is called again
    // Saves interrupt processing cycles
    extern void vw_rx_stop();

    // Block until the transmitter is idle
    extern void vw_wait_tx();

    // Block until a message is available
    extern void vw_wait_rx();
    // or for a max time
    extern uint8_t vw_wait_rx_max(unsigned long milliseconds);

    // Send a message with the given length. Returns almost immediately,
    // and message will be sent at the right timing by interrupts
    // Returns true if the message was accepted for transmissions
    // Returns false if the message is too long (>VW_MAX_MESSAGE_LEN - 3)
    extern uint8_t vw_send(uint8_t* buf, uint8_t len);

    // Returns true if an unread message is available
    extern uint8_t vw_have_message();

    // If a message is available (good checksum or not), copies
    // up to *len octets to buf.
    // Returns true if there was a message and the checksum was good
    extern uint8_t vw_get_message(uint8_t* buf, uint8_t* len);
}

#endif