altos: Add Pico Beacon code as ao_aprs.c

[fw/altos] / src / drivers / ao_aprs.c

/** 
 * http://ad7zj.net/kd7lmo/aprsbeacon_code.html
 *
 * @mainpage Pico Beacon
 *
 * @section overview_sec Overview
 *
 * The Pico Beacon is an APRS based tracking beacon that operates in the UHF 420-450MHz band.  The device utilizes a 
 * Microchip PIC 18F2525 embedded controller, Motorola M12+ GPS engine, and Analog Devices AD9954 DDS.  The device is capable
 * of generating a 1200bps A-FSK and 9600 bps FSK AX.25 compliant APRS (Automatic Position Reporting System) message.


 *
 * @section history_sec Revision History
 *
 * @subsection v305 V3.05
 * 23 Dec 2006, Change include; (1) change printf format width to conform to ANSI standard when new CCS 4.xx compiler released.
 *
 *
 * @subsection v304 V3.04
 * 10 Jan 2006, Change include; (1) added amplitude control to engineering mode,
 *                                     (2) corrected number of bytes reported in log,
 *                                     (3) add engineering command to set high rate position reports (5 seconds), and
 *                                     (4) corrected size of LOG_COORD block when searching for end of log.
 *
 * @subsection v303 V3.03
 * 15 Sep 2005, Change include; (1) removed AD9954 setting SDIO as input pin, 
 *                                     (2) additional comments and Doxygen tags,
 *                                     (3) integration and test code calculates DDS FTW,
 *                                     (4) swapped bus and reference analog input ports (hardware change),
 *                                     (5) added message that indicates we are reading flash log and reports length,
 *                                     (6) report bus voltage in 10mV steps, and
 *                                     (7) change log type enumerated values to XORed nibbles for error detection.
 *
 *
 * @subsection v302 V3.02
 * 6 Apr 2005, Change include; (1) corrected tracked satellite count in NMEA-0183 $GPGGA message,
 *                                    (2) Doxygen documentation clean up and additions, and
 *                                    (3) added integration and test code to baseline.
 *
 * 
 * @subsection v301 V3.01
 * 13 Jan 2005, Renamed project and files to Pico Beacon.
 *
 *
 * @subsection v300 V3.00
 * 15 Nov 2004, Change include; (1) Micro Beacon extreme hardware changes including integral transmitter,
 *                                     (2) PIC18F2525 processor,
 *                                     (3) AD9954 DDS support functions,
 *                                     (4) added comments and formatting for doxygen,
 *                                     (5) process GPS data with native Motorola protocol,
 *                                     (6) generate plain text $GPGGA and $GPRMC messages,
 *                                     (7) power down GPS 5 hours after lock,
 *                                     (8) added flight data recorder, and
 *                                     (9) added diagnostics terminal mode.
 *
 * 
 * @subsection v201 V2.01
 * 30 Jan 2004, Change include; (1) General clean up of in-line documentation, and 
 *                                     (2) changed temperature resolution to 0.1 degrees F.
 *
 * 
 * @subsection v200 V2.00
 * 26 Oct 2002, Change include; (1) Micro Beacon II hardware changes including PIC18F252 processor,
 *                                     (2) serial EEPROM, 
 *                                     (3) GPS power control, 
 *                                     (4) additional ADC input, and 
 *                                     (5) LM60 temperature sensor.                            
 *
 *
 * @subsection v101 V1.01
 * 5 Dec 2001, Change include; (1) Changed startup message, and 
 *                                    (2) applied SEPARATE pragma to several methods for memory usage.
 *
 *
 * @subsection v100 V1.00
 * 25 Sep 2001, Initial release.  Flew ANSR-3 and ANSR-4.
 * 


 *
 *
 * @section copyright_sec Copyright
 *
 * Copyright (c) 2001-2009 Michael Gray, KD7LMO


 *
 *
 * @section gpl_sec GNU General Public License
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *  


 * 
 * 
 * @section design Design Details
 *
 * Provides design details on a variety of the components that make up the Pico Beacon.
 *
 *  @subpage power
 */

/**
 *  @page power Power Consumption
 *
 *  Measured DC power consumption.
 * 
 *  3VDC prime power current 

 *
 *    7mA Held in reset 

 *   18mA Processor running, all I/O off 

 *  110mA GPS running 

 *  120mA GPS running w/antenna 

 *  250mA DDS running and GPS w/antenna 

 *  420mA DDS running, GPS w/antenna, and PA chain on with no RF 

 *  900mA Transmit 

 *
 */

// Hardware specific configuration.
#include <18f2525.h>
#device ADC=10

// NOTE: Even though we are using an external clock, we set the HS oscillator mode to
//       make the PIC 18F252 work with our external clock which is a clipped 1V P-P sine wave.
#fuses HS,NOWDT,NOPROTECT,NOPUT,NOBROWNOUT,NOLVP

// C runtime library definitions.
#include 
#include 

// These compiler directives set the clock, SPI/I2C ports, and I/O configuration.

// TCXO frequency
#use delay(clock=19200000)

// Engineering and data extracation port.
#use rs232(baud=57600, xmit=PIN_B7, rcv=PIN_B6, STREAM=PC_HOST)

// GPS engine 
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)

#use i2c (master, scl=PIN_C3, sda=PIN_C4)

#use fast_io(A)
#use fast_io(B)
#use fast_io(C)

// We define types that are used for all variables.  These are declared
// because each processor has a different sizes for int and long.
// The PIC compiler defines int8_t, int16_t, and int32_t.

/// Boolean value { false, true }
typedef boolean bool_t;

/// Signed 8-bit number in the range -128 through 127.
typedef signed int8 int8_t;

/// Unsigned 8-bit number in the range 0 through 255.
typedef unsigned int8 uint8_t;

/// Signed 16-bit number in the range -32768 through 32767.
typedef signed int16 int16_t;

/// Unsigned 16-bit number in the range 0 through 65535.
typedef unsigned int16 uint16_t;

/// Signed 32-bit number in the range -2147483648 through 2147483647.
typedef signed int32 int32_t;

/// Unsigned 32-bit number in the range 0 through 4294967296.
typedef unsigned int32 uint32_t;

// Function and structure prototypes.  These are declared at the start of
// the file much like a C++ header file.

// Map I/O pin names to hardware pins.

/// Heartbeat LED - Port A2
#define IO_LED PIN_A2

/// AD9954 DDS Profile Select 0 - Port A3
#define IO_PS0 PIN_A3

/// UHF amplifier and PA chain - Port A4
#define IO_PTT PIN_A4

/// AD9954 DDS Update - Port A5
#define IO_UPDATE PIN_A5

/// AD9954 CS (Chip Select) - Port B0
#define IO_CS PIN_B0

/// GPS Engine Power - Port B1
#define IO_GPS_PWR PIN_B1

/// AD9954 DDS Profile Select 1 - Port C0
#define IO_PS1 PIN_C0

/// AD9954 DDS OSK (Output Shift Key) - Port C2
#define IO_OSK PIN_C2

/// GPS engine serial transmit pin - Port C6
#define IO_GPS_TXD PIN_C6

// Public methods, constants, and data structures for each class.

/// Operational modes of the AD9954 DDS for the ddsSetMode function.
enum DDS_MODE
{
    /// Device has not been initialized.
    DDS_MODE_NOT_INITIALIZED,

    /// Device in lowest power down mode.
    DDS_MODE_POWERDOWN,

    /// Generate FM modulated audio tones.
    DDS_MODE_AFSK,

    /// Generate true FSK tones.
    DDS_MODE_FSK
};

void ddsInit();
void ddsSetAmplitude (uint8_t amplitude);
void ddsSetOutputScale (uint16_t amplitude);
void ddsSetFSKFreq (uint32_t ftw0, uint32_t ftw1);
void ddsSetFreq (uint32_t freq);
void ddsSetFTW (uint32_t ftw);
void ddsSetMode (DDS_MODE mode);

void flashErase();
uint8_t flashGetByte ();
void flashReadBlock(uint32_t address, uint8_t *block, uint16_t length);
void flashSendByte(uint8_t value);
void flashSendAddress(uint32_t address);
void flashWriteBlock(uint32_t address, uint8_t *block, uint8_t length);

/// Type of GPS fix.
enum GPS_FIX_TYPE 
{
    /// No GPS FIX
    GPS_NO_FIX,

    /// 2D (Latitude/Longitude) fix.
    GPS_2D_FIX,

    /// 3D (Latitude/Longitude/Altitude) fix.
    GPS_3D_FIX
};

/// GPS Position information.
typedef struct 
{
    /// Flag that indicates the position information has been updated since it was last checked.
    bool_t updateFlag;

    /// Month in UTC time.
    uint8_t month;

    /// Day of month in UTC time.
    uint8_t day;

    /// Hours in UTC time.
    uint8_t hours;

    /// Minutes in UTC time.
    uint8_t minutes;

    /// Seconds in UTC time.
    uint8_t seconds;

    /// Year in UTC time.
    uint16_t year;

    /// Latitude in milli arc-seconds where + is North, - is South.
    int32_t latitude;

    /// Longitude in milli arc-seconds where + is East, - is West.
    int32_t longitude;

    /// Altitude in cm
    int32_t altitudeCM;

    /// Calculated altitude in feet
    int32_t altitudeFeet;

    /// 3D speed in cm/second.
    uint16_t vSpeed;

    /// 2D speed in cm/second.
    uint16_t hSpeed;

    /// Heading units of 0.1 degrees.
    uint16_t heading;

    /// DOP (Dilution of Precision)
    uint16_t dop;

    /// 16-bit number that represents status of GPS engine.
    uint16_t status;

    /// Number of tracked satellites used in the fix position.
    uint8_t trackedSats;

    /// Number of visible satellites.
    uint8_t visibleSats;
} GPSPOSITION_STRUCT;

void gpsInit();
bool_t gpsIsReady();
GPS_FIX_TYPE gpsGetFixType();
int32_t gpsGetPeakAltitude();
void gpsPowerOn();
bool_t gpsSetup();
void gpsUpdate();

int16_t lm92GetTemp();

/// Define the log record types.
enum LOG_TYPE 
{
    /// Time stamp the log was started.
    LOG_BOOTED = 0xb4,

    /// GPS coordinates.
    LOG_COORD = 0xa5,

    /// Temperature
    LOG_TEMPERATURE = 0x96,

    /// Bus voltage.
    LOG_VOLTAGE = 0x87
};

void logInit();
uint32_t logGetAddress();
void logType (LOG_TYPE type);
void logUint8 (uint8_t value);
void logInt16 (int16_t value);

bool_t serialHasData();
void serialInit();
uint8_t serialRead();
void serialUpdate();

uint16_t sysCRC16(uint8_t *buffer, uint8_t length, uint16_t crc);
void sysInit();
void sysLogVoltage();

/// 0% duty cycle (LED Off) constant for function timeSetDutyCycle
#define TIME_DUTYCYCLE_0 0

/// 10% duty cycle constant for function timeSetDutyCycle
#define TIME_DUTYCYCLE_10 1

/// 70% duty cycle constant for function timeSetDutyCycle
#define TIME_DUTYCYCLE_70 7

uint8_t timeGetTicks();
void timeInit();
void timeSetDutyCycle (uint8_t dutyCycle);
void timeUpdate();

/// Operational modes of the TNC for the tncSetMode function.
enum TNC_DATA_MODE
{
    /// No operation waiting for setup and configuration.
    TNC_MODE_STANDBY, 

    /// 1200 bps using A-FSK (Audio FSK) tones.
    TNC_MODE_1200_AFSK,

    /// 9600 bps using true FSK tones.
    TNC_MODE_9600_FSK
};

void tncInit();
bool_t tncIsFree();
void tncHighRate(bool_t state);
void tncSetMode (TNC_DATA_MODE dataMode);
void tnc1200TimerTick();
void tnc9600TimerTick();
void tncTxByte (uint8_t value);
void tncTxPacket(TNC_DATA_MODE dataMode);

/**
 *  @defgroup ADC Analog To Digital Converter
 *
 *  Control and manage the on board PIC A/D converter.
 *
 *  @{
 */

/// Filtered voltages using a single pole, low pass filter.
uint16_t adcMainBusVolt;

/// PIC ADC Channel number of the reference voltage.
#define ADC_REF 0

/// PIC ADC Channel number of the main bus voltage.
#define ADC_MAINBUS 1

/// Input diode drop in units of 0.01 volts.
#define MAIN_BUS_VOLT_OFFSET 20

/**
 *  Intialize the ADC subsystem.
 */
void adcInit()
{
    // Setup the ADC.
    setup_adc_ports(AN0_TO_AN1);
    setup_adc( ADC_CLOCK_DIV_32 );

    // Zero the ADC filters.
    adcMainBusVolt = 0;
}

/**
 *   Filtered main bus voltage in 10mV resolution.
 *
 *   @return voltage in 10mV steps
 */
uint16_t adcGetMainBusVolt()
{
    uint32_t volts;

    volts = (uint32_t) (adcMainBusVolt >> 3);

    volts = (volts * 330l) / 1023l;

    return (uint16_t) volts + MAIN_BUS_VOLT_OFFSET;
}

/** 
 *   Get the current ADC value for the main bus voltage.
 *
 *   @return ADC value in the range 0 to 1023
 */
uint16_t adcRawBusVolt()
{
    set_adc_channel(ADC_MAINBUS);
    delay_us(50);
    return read_adc();
}

/** 
 *   Get the current ADC value for the reference source voltage.
 *
 *   @return ADC value in the range 0 to 1023
 */
uint16_t adcRawRefVolt()
{
    set_adc_channel(ADC_REF);
    delay_us(50);
    return read_adc();
}

/**
 *   Read and filter the ADC channels for bus voltages.
 */
void adcUpdate(void)
{
    // Filter the bus voltage using a single pole low pass filter.
    set_adc_channel(ADC_MAINBUS);
    delay_us(50);
    adcMainBusVolt = read_adc() + adcMainBusVolt - (adcMainBusVolt >> 3);
}

/** @} */


/**
 *  @defgroup diag Diagnostics and Control
 *
 *  Functions for diagnostics and control of the hardware and flight data recorder.
 *
 *  @{
 */

/// Number of bytes per line to display when reading flight data recorder.
#define DIAG_BYTES_PER_LINE 32

/**
 *   Process the command to erase the data logger flash.
 */
void diagEraseFlash()
{
    // Confirm we want to erase the flash with the key sequence 'yes' .
    fprintf (PC_HOST, "Are you sure (yes)?  ");

    if (fgetc(PC_HOST) != 'y')
        return;

    if (fgetc(PC_HOST) != 'e')
        return;

    if (fgetc(PC_HOST) != 's')
        return;

    if (fgetc(PC_HOST) != 13)
        return;

    // User feedback and erase the part.
    fprintf (PC_HOST, "Erasing flash...");

    flashErase();

    fprintf (PC_HOST, "done.\n\r");
}

/**
 *   Display the engineering mode menu.
 */
void diagMenu()
{
    // User interface.
    fprintf (PC_HOST, "Options: (e)rase Flash, (r)ead Flash\n\r");
    fprintf (PC_HOST, "         Toggle (L)ED\n\r");
    fprintf (PC_HOST, "         (P)TT - Push To Transmit\n\r");
    fprintf (PC_HOST, "         (f)requencey down, (F)requency up - 1KHz step\n\r");
    fprintf (PC_HOST, "         (c)hannel down, (C)hannel up - 25KHz step\n\r");
    fprintf (PC_HOST, "         (a)mplitude down, (A)mplitude up - 0.5 dB steps\n\r");
    fprintf (PC_HOST, "         e(x)it engineering mode\n\r");
}

/**
 *   Process the command to dump the contents of the data logger flash.
 */
void diagReadFlash()
{
    bool_t dataFoundFlag, userStopFlag;
    uint8_t i, buffer[DIAG_BYTES_PER_LINE];
    uint32_t address;

    // Set the initial conditions to read the flash.
    address = 0x0000;
    userStopFlag = false;

    do 
    {
        // Read each block from the flash device.
        flashReadBlock (address, buffer, DIAG_BYTES_PER_LINE);

        // This flag will get set if any data byte is not equal to 0xff (erase flash state)
        dataFoundFlag = false;

        // Display the address.
        fprintf (PC_HOST, "%08lx ", address);

        // Display each byte in the line.
        for (i = 0; i < DIAG_BYTES_PER_LINE; ++i) 
        {
            fprintf (PC_HOST, "%02x", buffer[i]);

            // Set this flag if the cell is not erased.
            if (buffer[i] != 0xff)
                dataFoundFlag = true;

            // Any key will abort the transfer.
            if (kbhit(PC_HOST))
                userStopFlag = true;
        } // END for

        //  at the end of each line.
        fprintf (PC_HOST, "\n\r");

        // Advance to the next block of memory.
        address += DIAG_BYTES_PER_LINE;
    } while (dataFoundFlag && !userStopFlag);

    // Feedback to let the user know why the transfer stopped.
    if (userStopFlag)
        fprintf (PC_HOST, "User aborted download!\n\r");
}

void diag1PPS()
{
    uint16_t timeStamp, lastTimeStamp;

    lastTimeStamp = 0x0000;

    gpsPowerOn();

    for (;;)
    {
        timeStamp = CCP_2;

        if (timeStamp != lastTimeStamp)
        {
            delay_ms (10);

            timeStamp = CCP_2;

            fprintf (PC_HOST, "%lu %lu\n\r", timeStamp, (timeStamp - lastTimeStamp));

            lastTimeStamp = timeStamp;
        }
    }
}

/**
 *   Process diagnostic commands through the debug RS-232 port.
 */
void diagPort()
{
    bool_t diagDoneFlag, ledFlag, paFlag, showSettingsFlag;
    uint8_t command, amplitude;
    uint32_t freqHz;

    // If the input is low, we aren't connected to the RS-232 device so continue to boot.
    if (!input(PIN_B6))
        return;

    fprintf (PC_HOST, "Engineering Mode\n\r");
    fprintf (PC_HOST, "Application Built %s %s\n\r", __DATE__, __TIME__);

    // Current state of the status LED.
    ledFlag = false;
    output_bit (IO_LED, ledFlag);

    // This flag indicates we are ready to leave the diagnostics mode.
    diagDoneFlag = false;

    // Current state of the PA.
    paFlag = false;

    // Flag that indicate we should show the current carrier frequency.
    showSettingsFlag = false;

    // Set the initial carrier frequency and amplitude.
    freqHz = 445950000;
    amplitude = 0;

    // Wait for the exit command.
    while (!diagDoneFlag) 
    {
        // Wait for the user command.
        command = fgetc(PC_HOST);

        // Decode and process the key stroke.
        switch (command) 
        {
            case 'e':
                diagEraseFlash();
                logInit();
                break;

            case 'l':
            case 'L':
                ledFlag = (ledFlag ? false : true);
                output_bit (IO_LED, ledFlag);
                break;

            case 'h':
            case 'H':
            case '?':
                diagMenu();
                break;

            case 'r':
                diagReadFlash();
                break;

            case 't':
                tncHighRate (true);
                fprintf (PC_HOST, "Set high rate TNC.\n\r");    
                break;

            case 'f':
                freqHz -= 1000;
                ddsSetFreq (freqHz);

                // Display the new frequency.
                showSettingsFlag = true;
                break;

            case 'F':
                freqHz += 1000;
                ddsSetFreq (freqHz);

                // Display the new frequency.
                showSettingsFlag = true;
                break;

            case 'c':
                freqHz -= 25000;
                ddsSetFreq (freqHz);

                // Display the new frequency.
                showSettingsFlag = true;
                break;

            case 'C':
                freqHz += 25000;
                ddsSetFreq (freqHz);

                // Display the new frequency.
                showSettingsFlag = true;
                break;

            case 'p':
            case 'P':
                ddsSetFreq (freqHz);

                paFlag = (paFlag ? false : true);
                output_bit (IO_PTT, paFlag);
                output_bit (IO_OSK, paFlag);

                if (paFlag)
                {
                    ddsSetMode (DDS_MODE_AFSK);             
                    ddsSetAmplitude (amplitude);
                } else
                    ddsSetMode (DDS_MODE_POWERDOWN);

                break;

            case 'a':
                if (amplitude != 200)
                {
                    amplitude += 5;
                    ddsSetAmplitude (amplitude);

                    // Display the new amplitude.
                    showSettingsFlag = true;
                }
                break;

            case 'A':
                if (amplitude != 0)
                {
                    amplitude -= 5;
                    ddsSetAmplitude (amplitude);

                    // Display the new amplitude.
                    showSettingsFlag = true;
                }
                break;

            case 'g':
                diag1PPS();
                break;

            case 'x':
                diagDoneFlag = true;
                break;

            default:
                fprintf (PC_HOST, "Invalid command.  (H)elp for menu.\n\r");
                break;
        } // END switch

        // Display the results of any user requests or commands.
        if (showSettingsFlag) 
        {
            showSettingsFlag = false;

            fprintf (PC_HOST, "%03ld.%03ld MHz  ", freqHz / 1000000, (freqHz / 1000) % 1000);
            fprintf (PC_HOST, "%d.%01ddBc\n\r", amplitude / 10, amplitude % 10);

        } // END if

    } // END while

    // Let the user know we are done with this mode.
    fprintf (PC_HOST, "Exit diagnostic mode.\n\r");

    return;
}

/** @} */


/**
 *  @defgroup DDS AD9954 DDS (Direct Digital Synthesizer)
 *
 *  Functions to control the Analog Devices AD9954 DDS.
 *
 *  @{
 */

/// AD9954 CFR1 - Control functions including RAM, profiles, OSK, sync, sweep, SPI, and power control settings.
#define DDS_AD9954_CFR1 0x00

/// AD9954 CFR2 - Control functions including sync, PLL multiplier, VCO range, and charge pump current.
#define DDS_AD9954_CFR2 0x01

/// AD9954 ASF - Auto ramp rate speed control and output scale factor (0x0000 to 0x3fff).
#define DDS_AD9954_ASF 0x02

/// AD9954 ARR - Amplitude ramp rate for OSK function.
#define DDS_AD9954_ARR 0x03

/// AD9954 FTW0 - Frequency tuning word 0.
#define DDS_AD9954_FTW0 0x04

/// AD9954 FTW1 - Frequency tuning word 1
#define DDS_AD9954_FTW1 0x06

/// AD9954 NLSCW - Negative Linear Sweep Control Word used for spectral shaping in FSK mode
#define DDS_AD9954_NLSCW 0x07

/// AD9954 PLSCW - Positive Linear Sweep Control Word used for spectral shaping in FSK mode
#define DDS_AD9954_PLSCW 0x08

/// AD9954 RSCW0 - RAM Segment Control Word 0
#define DDS_AD9954_RWCW0 0x07

/// AD9954 RSCW0 - RAM Segment Control Word 1
#define DDS_AD9954_RWCW1 0x08

/// AD9954 RAM segment
#define DDS_RAM 0x0b

/// Current operational mode.
DDS_MODE ddsMode;

/// Number of digits in DDS frequency to FTW conversion.
#define DDS_FREQ_TO_FTW_DIGITS 9

/// Array of multiplication factors used to convert frequency to the FTW.
const uint32_t DDS_MULT[DDS_FREQ_TO_FTW_DIGITS] = { 11, 7, 7, 3, 4, 8, 4, 9, 1 };

/// Array of divisors used to convert frequency to the FTW.
const uint32_t DDS_DIVISOR[DDS_FREQ_TO_FTW_DIGITS - 1] = { 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000 };

/// Lookup table to convert dB amplitude scale in 0.5 steps to a linear DDS scale factor.
const uint16_t DDS_AMP_TO_SCALE[] = 
{ 
    16383, 15467, 14601, 13785, 13013, 12286, 11598, 10949, 10337, 9759, 9213, 8697, 
    8211, 7752, 7318, 6909, 6522, 6157, 5813, 5488, 5181, 4891, 4617, 4359, 4115, 3885, 3668, 3463, 
    3269, 3086, 2913, 2750, 2597, 2451, 2314, 2185, 2062, 1947, 1838, 1735, 1638 
};


/// Frequency Word List - 4.0KHz FM frequency deviation at 81.15MHz  (445.950MHz)
const uint32_t freqTable[256] = 
{
    955418300, 955419456, 955420611, 955421765, 955422916, 955424065, 955425210, 955426351, 
    955427488, 955428618, 955429743, 955430861, 955431971, 955433073, 955434166, 955435249, 
    955436322, 955437385, 955438435, 955439474, 955440500, 955441513, 955442511, 955443495, 
    955444464, 955445417, 955446354, 955447274, 955448176, 955449061, 955449926, 955450773, 
    955451601, 955452408, 955453194, 955453960, 955454704, 955455426, 955456126, 955456803, 
    955457457, 955458088, 955458694, 955459276, 955459833, 955460366, 955460873, 955461354, 
    955461809, 955462238, 955462641, 955463017, 955463366, 955463688, 955463983, 955464250, 
    955464489, 955464701, 955464884, 955465040, 955465167, 955465266, 955465337, 955465380, 
    955465394, 955465380, 955465337, 955465266, 955465167, 955465040, 955464884, 955464701, 
    955464489, 955464250, 955463983, 955463688, 955463366, 955463017, 955462641, 955462238, 
    955461809, 955461354, 955460873, 955460366, 955459833, 955459276, 955458694, 955458088, 
    955457457, 955456803, 955456126, 955455426, 955454704, 955453960, 955453194, 955452408, 
    955451601, 955450773, 955449926, 955449061, 955448176, 955447274, 955446354, 955445417, 
    955444464, 955443495, 955442511, 955441513, 955440500, 955439474, 955438435, 955437385, 
    955436322, 955435249, 955434166, 955433073, 955431971, 955430861, 955429743, 955428618, 
    955427488, 955426351, 955425210, 955424065, 955422916, 955421765, 955420611, 955419456, 
    955418300, 955417144, 955415989, 955414836, 955413684, 955412535, 955411390, 955410249, 
    955409113, 955407982, 955406857, 955405740, 955404629, 955403528, 955402435, 955401351, 
    955400278, 955399216, 955398165, 955397126, 955396100, 955395088, 955394089, 955393105, 
    955392136, 955391183, 955390246, 955389326, 955388424, 955387540, 955386674, 955385827, 
    955385000, 955384192, 955383406, 955382640, 955381896, 955381174, 955380474, 955379797, 
    955379143, 955378513, 955377906, 955377324, 955376767, 955376235, 955375728, 955375246, 
    955374791, 955374362, 955373959, 955373583, 955373234, 955372912, 955372618, 955372350, 
    955372111, 955371900, 955371716, 955371560, 955371433, 955371334, 955371263, 955371220, 
    955371206, 955371220, 955371263, 955371334, 955371433, 955371560, 955371716, 955371900, 
    955372111, 955372350, 955372618, 955372912, 955373234, 955373583, 955373959, 955374362, 
    955374791, 955375246, 955375728, 955376235, 955376767, 955377324, 955377906, 955378513, 
    955379143, 955379797, 955380474, 955381174, 955381896, 955382640, 955383406, 955384192, 
    955385000, 955385827, 955386674, 955387540, 955388424, 955389326, 955390246, 955391183, 
    955392136, 955393105, 955394089, 955395088, 955396100, 955397126, 955398165, 955399216, 
    955400278, 955401351, 955402435, 955403528, 955404629, 955405740, 955406857, 955407982, 
    955409113, 955410249, 955411390, 955412535, 955413684, 955414836, 955415989, 955417144
};

/**
 *   Initialize the DDS regsiters and RAM.
 */
void ddsInit()
{
    // Setup the SPI port for the DDS interface.    
    setup_spi( SPI_MASTER | SPI_L_TO_H | SPI_CLK_DIV_4 | SPI_XMIT_L_TO_H );    

    // Set the initial DDS mode.  The ddsSetMode function uses this value to make the desired DDS selections. 
    ddsMode = DDS_MODE_NOT_INITIALIZED;

    // Set the DDS operational mode.
    ddsSetMode (DDS_MODE_POWERDOWN);

    // Set the output to full scale.
    ddsSetOutputScale (0x3fff);

    // CFR2 (Control Function Register No. 2)
    output_low (IO_CS);
    spi_write (DDS_AD9954_CFR2);

    spi_write (0x00);     // Unused register bits
    spi_write (0x00);
    spi_write (0x9c);     // 19x reference clock multipler, high VCO range, nominal charge pump current
    output_high (IO_CS);

    // ARR (Amplitude Ramp Rate) to 15mS for OSK
    output_low (IO_CS);
    spi_write (DDS_AD9954_ARR);

    spi_write (83);
    output_high (IO_CS);

    // Strobe the part so we apply the updates.
    output_high (IO_UPDATE);
    output_low (IO_UPDATE);
}

/**
 *  Set DDS amplitude value in the range 0 to 16383 where 16383 is full scale.  This value is a 
 *  linear multiplier and needs to be scale for RF output power in log scale.
 *
 *  @param scale in the range 0 to 16383
 */
void ddsSetOutputScale (uint16_t scale)
{
    // Set ASF (Amplitude Scale Factor)
    output_low (IO_CS);
    spi_write (DDS_AD9954_ASF);

    spi_write ((scale >> 8) & 0xff);
    spi_write (scale & 0xff);

    output_high (IO_CS);
    
    // Strobe the DDS to set the amplitude.
    output_high (IO_UPDATE);
    output_low (IO_UPDATE);
}

/**
 *   Set the DDS amplitude in units of dBc of full scale where 1 is 0.1 dB.  For example, a value of 30 is 3dBc
 *   or a value of 85 is 8.5dBc.
 *
 *   @param amplitude in 0.1 dBc of full scale
 */ 
void ddsSetAmplitude (uint8_t amplitude)
{
    // Range limit based on the lookup table size.
    if (amplitude > 200)
        return;

    // Set the linear DDS ASF (Amplitude Scale Factor) based on the dB lookup table.
    ddsSetOutputScale (DDS_AMP_TO_SCALE[amplitude / 5]);

    // Toggle the DDS output low and then high to force it to ramp to the new output level setting.
    output_low (IO_OSK);
    delay_ms(25); 

    output_high (IO_OSK);
    delay_ms(25); 
}

/**
 *  Set DDS frequency tuning word.  The output frequency is equal to RefClock * (ftw / 2 ^ 32).
 *
 *  @param ftw Frequency Tuning Word
 */
void ddsSetFTW (uint32_t ftw)
{
    // Set FTW0 (Frequency Tuning Word 0)
    output_low (IO_CS);
    spi_write (DDS_AD9954_FTW0);

    spi_write ((ftw >> 24) & 0xff);
    spi_write ((ftw >> 16) & 0xff);
    spi_write ((ftw >> 8) & 0xff);
    spi_write (ftw & 0xff);

    output_high (IO_CS);
    
    // Strobe the DDS to set the frequency.
    output_high (IO_UPDATE);
    output_low (IO_UPDATE);     
}

/**
 *   Convert frequency in hertz to 32-bit DDS FTW (Frequency Tune Word).
 *
 *   @param freq frequency in Hertz
 *
 */
void ddsSetFreq(uint32_t freq)
{
    uint8_t i;
    uint32_t ftw;
    
    // To avoid rounding errors with floating point math, we do a long multiply on the data.
    ftw = freq * DDS_MULT[0];
    
    for (i = 0; i < DDS_FREQ_TO_FTW_DIGITS - 1; ++i)
        ftw += (freq * DDS_MULT[i+1]) / DDS_DIVISOR[i];
    
    ddsSetFTW (ftw);
}

/**
 *  Set DDS frequency tuning word for the FSK 0 and 1 values.  The output frequency is equal 
 *  to RefClock * (ftw / 2 ^ 32).
 *
 *  @param ftw0 frequency tuning word for the FSK 0 value
 *  @param ftw1 frequency tuning word for the FSK 1 value
 */
void ddsSetFSKFreq (uint32_t ftw0, uint32_t ftw1)
{
    // Set FTW0 (Frequency Tuning Word 0)
    output_low (IO_CS);
    spi_write (DDS_AD9954_FTW0);

    spi_write ((ftw0 >> 24) & 0xff);
    spi_write ((ftw0 >> 16) & 0xff);
    spi_write ((ftw0 >> 8) & 0xff);
    spi_write (ftw0 & 0xff);

    output_high (IO_CS);
    
    // Set FTW0 (Frequency Tuning Word 1)
    output_low (IO_CS);
    spi_write (DDS_AD9954_FTW1);

    spi_write ((ftw1 >> 24) & 0xff);
    spi_write ((ftw1 >> 16) & 0xff);
    spi_write ((ftw1 >> 8) & 0xff);
    spi_write (ftw1 & 0xff);

    output_high (IO_CS);
    
    // Strobe the DDS to set the frequency.
    output_high (IO_UPDATE);
    output_low (IO_UPDATE);     
}

/** 
 *   Set the DDS to run in A-FSK, FSK, or PSK31 mode
 *
 *   @param mode DDS_MODE_APRS, DDS_MODE_PSK31, or DDS_MODE_HF_APRS constant
 */
void ddsSetMode (DDS_MODE mode)
{
    // Save the current mode.
    ddsMode = mode;

    switch (mode) 
    {
        case DDS_MODE_POWERDOWN:
            // CFR1 (Control Function Register No. 1)
            output_low (IO_CS);
            spi_write (DDS_AD9954_CFR1);
        
            spi_write (0x00);
            spi_write (0x00);
            spi_write (0x00);
            spi_write (0xf0);  // Power down all subsystems.
            output_high (IO_CS);
            break;

        case DDS_MODE_AFSK:
            // CFR1 (Control Function Register No. 1)
            output_low (IO_CS);
            spi_write (DDS_AD9954_CFR1);
        
            spi_write (0x03);  // OSK Enable and Auto OSK keying
            spi_write (0x00);
            spi_write (0x00);
            spi_write (0x40);  // Power down comparator circuit
            output_high (IO_CS);
            break;

        case DDS_MODE_FSK:
            // CFR1 (Control Function Register No. 1)
            output_low (IO_CS);
            spi_write (DDS_AD9954_CFR1);

            spi_write (0x03);  // Clear RAM Enable, OSK Enable, Auto OSK keying
            spi_write (0x00);
            spi_write (0x00);
            spi_write (0x40);  // Power down comparator circuit
            output_high (IO_CS);

            // NOTE: The sweep rate requires 1/4 of a bit time (26uS) to transition.
            // 6KHz delta = 70641 counts = (6KHz / 364.8MHz) * 2 ^ 32
            // SYNC_CLK = 91.2MHz  1/91.2MHz * 70641 * 1/29 = 26.7uS

            // NLSCW (Negative Linear Sweep Control Word)
            output_low (IO_CS);
            spi_write (DDS_AD9954_NLSCW);

            spi_write (1);     // Falling sweep ramp rate word
            spi_write (0x00);  // Delta frequency tuning word
            spi_write (0x00);
            spi_write (0x00);
            spi_write (250); 
            output_high (IO_CS);

            // PLSCW (Positive Linear Sweep Control Word)
            output_low (IO_CS);
            spi_write (DDS_AD9954_PLSCW);

            spi_write (1);     // Rising sweep ramp rate word
            spi_write (0x00);  // Delta frequency tuning word
            spi_write (0x00);
            spi_write (0x00);
            spi_write (250); 
            output_high (IO_CS);
            break;
    } // END switch
    
    // Strobe the DDS to change the mode.
    output_high (IO_UPDATE);
    output_low (IO_UPDATE);      
}

/** @} */

/**
 *  @defgroup flash Flash Manager
 *
 *  Functions to control the ST MP25P80 serial flash device.
 *
 *  @{
 */

/// Flash Chip Select - Port B3
#define FLASH_CS PIN_B3

/// Flash Clock - Port B5
#define FLASH_CLK PIN_B5

/// Flash Data Input - Port B4
#define FLASH_D PIN_B4

/// Flash Data Output - Port B2
#define FLASH_Q PIN_B2

/** 
 *   Determine if a flash write or erase operation is currently in progress.
 *
 *   @return true if write/erase in progress
 */
bool_t flashIsWriteInProgress()
{
    uint8_t status;

    output_low (FLASH_CS);

    // Read Status Register (RDSR) flash command.
    flashSendByte (0x05);

    status = flashGetByte();

    output_high (FLASH_CS);

    return (((status & 0x01) == 0x01) ? true : false);
}

/**
 *   Read a block of memory from the flash device.
 *
 *   @param address of desired location in the range 0x00000 to 0xFFFFF (1MB)
 *   @param block pointer to locate of data block
 *   @param length number of bytes to read
 */
void flashReadBlock(uint32_t address, uint8_t *block, uint16_t length)
{
    uint16_t i;
    
    output_low (FLASH_CS);

    // Read Data Byte(s) (READ) flash command.
    flashSendByte (0x03);
    flashSendAddress (address);
    
    for (i = 0; i < length; ++i)
        *block++ = flashGetByte();
    
    output_high (FLASH_CS);
}

/**
 *   Write a block of memory to the flash device.
 *
 *   @param address of desired location in the range 0x00000 to 0xFFFFF (1MB)
 *   @param block pointer data block to write
 *   @param length number of bytes to write
 */
void flashWriteBlock(uint32_t address, uint8_t *block, uint8_t length)
{
    uint8_t i;

    output_low (FLASH_CS);
    // Write Enable (WREN) flash command.
    flashSendByte (0x06);
    output_high (FLASH_CS);
    
    output_low (FLASH_CS);
    // Page Program (PP) flash command.
    flashSendByte (0x02);
    flashSendAddress (address);
    
    for (i = 0; i < length; ++i) 
    {
        // Send each byte in the data block.
        flashSendByte (*block++);

        // Track the address in the flash device.
        ++address;

        // If we cross a page boundary (a page is 256 bytes) we need to stop and send the address again.
        if ((address & 0xff) == 0x00) 
        {
            output_high (FLASH_CS);

            // Write this block of data.
            while (flashIsWriteInProgress());

            output_low (FLASH_CS);
            // Write Enable (WREN) flash command.
            flashSendByte (0x06);
            output_high (FLASH_CS);

            output_low (FLASH_CS);
            // Page Program (PP) flash command.
            flashSendByte (0x02);
            flashSendAddress (address);
        } // END if
    } // END for    

    output_high (FLASH_CS);

    // Wait for the final write operation to complete.
    while (flashIsWriteInProgress());
}

/** 
 *   Erase the entire flash device (all locations set to 0xff).
 */
void flashErase()
{
    output_low (FLASH_CS);
    // Write Enable (WREN) flash command.
    flashSendByte (0x06);
    output_high (FLASH_CS);
    
    output_low (FLASH_CS);
    // Bulk Erase (BE) flash command.
    flashSendByte (0xc7);
    output_high (FLASH_CS);

    while (flashIsWriteInProgress());
}

/**
 *   Read a single byte from the flash device through the serial interface.  This function
 *   only controls the clock line.  The chip select must be configured before calling
 *   this function.
 *
 *   @return byte read from device
 */
uint8_t flashGetByte()
{
    uint8_t i, value;
    
    value = 0;      
    
    // Bit bang the 8-bits.
    for (i = 0; i < 8; ++i) 
    {
        // Data is ready on the rising edge of the clock.
        output_high (FLASH_CLK);

        // MSB is first, so shift left.
        value = value << 1;
    
        if (input (FLASH_Q))
            value = value | 0x01;
    
        output_low (FLASH_CLK);
    } // END for

    return value;
}

/**
 *   Initialize the flash memory subsystem.
 */
void flashInit()
{
    // I/O lines to control flash.
    output_high (FLASH_CS);
    output_low (FLASH_CLK);
    output_low (FLASH_D);
}

/**
 *   Write a single byte to the flash device through the serial interface.  This function
 *   only controls the clock line.  The chip select must be configured before calling
 *   this function.
 *
 *   @param value byte to write to device
 */
void flashSendByte(uint8_t value)
{
    uint8_t i;
    
    // Bit bang the 8-bits.
    for (i = 0; i < 8; ++i) 
    {
        // Drive the data input pin.
        if ((value & 0x80) == 0x80)
            output_high (FLASH_D);
        else
            output_low (FLASH_D);
        
        // MSB is first, so shift leeft.
        value = value << 1;
        
        // Data is accepted on the rising edge of the clock.
        output_high (FLASH_CLK);
        output_low (FLASH_CLK);
    } // END for
}

/**
 *    Write the 24-bit address to the flash device through the serial interface.  This function
 *   only controls the clock line.  The chip select must be configured before calling
 *   this function.
 *
 *   @param address 24-bit flash device address
 */
void flashSendAddress(uint32_t address)
{
    uint8_t i;
    
    // Bit bang the 24-bits.
    for (i = 0; i < 24; ++i) 
    {
        // Drive the data input pin.
        if ((address & 0x800000) == 0x800000)
            output_high (FLASH_D);
        else
            output_low (FLASH_D);
        
        // MSB is first, so shift left.
        address = address << 1;

        // Data is accepted on the rising edge of the clock.
        output_high (FLASH_CLK);
        output_low (FLASH_CLK);
    } // END for
}

/** @} */

/**
 *  @defgroup GPS Motorola M12+ GPS Engine
 *
 *  Functions to control the Motorola M12+ GPS engine in native binary protocol mode.
 *
 *  @{
 */

/// The maximum length of a binary GPS engine message.
#define GPS_BUFFER_SIZE 50

/// GPS parse engine state machine values.
enum GPS_PARSE_STATE_MACHINE 
{
    /// 1st start character '@'
    GPS_START1,

    /// 2nd start character '@'
    GPS_START2,

    /// Upper case 'A' - 'Z' message type
    GPS_COMMAND1,

    /// Lower case 'a' - 'z' message type
    GPS_COMMAND2,

    /// 0 - xx bytes based on message type 'Aa'
    GPS_READMESSAGE,

    /// 8-bit checksum
    GPS_CHECKSUMMESSAGE,

    /// End of message - Carriage Return
    GPS_EOMCR,

    /// End of message - Line Feed
    GPS_EOMLF
};

/// Index into gpsBuffer used to store message data.
uint8_t gpsIndex;

/// State machine used to parse the GPS message stream.
GPS_PARSE_STATE_MACHINE gpsParseState;

/// Buffer to store data as it is read from the GPS engine.
uint8_t gpsBuffer[GPS_BUFFER_SIZE]; 

/// Peak altitude detected while GPS is in 3D fix mode.
int32_t gpsPeakAltitude;

/// Checksum used to verify binary message from GPS engine.
uint8_t gpsChecksum;

/// Last verified GPS message received.
GPSPOSITION_STRUCT gpsPosition;

/**
 *   Get the type of fix.
 *
 *   @return gps fix type enumeration
 */
GPS_FIX_TYPE gpsGetFixType()
{
    // The upper 3-bits determine the fix type.
    switch (gpsPosition.status & 0xe000) 
    {
        case 0xe000:
            return GPS_3D_FIX;

        case 0xc000:
            return GPS_2D_FIX;
    
        default:
            return GPS_NO_FIX;
    } // END switch
}

/**
 *  Peak altitude detected while GPS is in 3D fix mode since the system was booted.
 *
 *  @return altitude in feet
 */
int32_t gpsGetPeakAltitude()
{
    return gpsPeakAltitude;
}

/** 
 *    Initialize the GPS subsystem.
 */
void gpsInit()
{
    // Initial parse state.
    gpsParseState = GPS_START1;

    // Assume we start at sea level.
    gpsPeakAltitude = 0;

    // Clear the structure that stores the position message.
    memset (&gpsPosition, 0, sizeof(GPSPOSITION_STRUCT));

    // Setup the timers used to measure the 1-PPS time period.
    setup_timer_3(T3_INTERNAL | T3_DIV_BY_1);
    setup_ccp2 (CCP_CAPTURE_RE | CCP_USE_TIMER3);
}

/**
 *   Determine if new GPS message is ready to process.  This function is a one shot and
 *   typically returns true once a second for each GPS position fix.
 *
 *   @return true if new message available; otherwise false
 */
bool_t gpsIsReady()
{
    if (gpsPosition.updateFlag) 
    {
        gpsPosition.updateFlag = false;
        return true;
    } // END if

    return false;
}

/**
 *   Calculate NMEA-0183 message checksum of buffer that is length bytes long.
 *
 *   @param buffer pointer to data buffer.
 *   @param length number of bytes in buffer.
 *
 *   @return checksum of buffer
 */
uint8_t gpsNMEAChecksum (uint8_t *buffer, uint8_t length)
{
    uint8_t i, checksum;

    checksum = 0;

    for (i = 0; i < length; ++i)
        checksum ^= buffer[i];

    return checksum;
}

/**
 *   Verify the GPS engine is sending the @@Hb position report message.  If not,
 *   configure the GPS engine to send the desired report.
 *
 *   @return true if GPS engine operation; otherwise false
 */
bool_t gpsSetup()
{
    uint8_t startTime, retryCount;

    // We wait 10 seconds for the GPS engine to respond to our message request.
    startTime = timeGetTicks();
    retryCount = 0;

    while (++retryCount < 10) 
    {
        // Read the serial FIFO and process the GPS messages.
        gpsUpdate();

        // If a GPS data set is available, then GPS is operational.
        if (gpsIsReady()) 
        {
            timeSetDutyCycle (TIME_DUTYCYCLE_10);
            return true;
        }

        if (timeGetTicks() > startTime) 
        {
            puts ("@@Hb\001\053\015\012");
            startTime += 10;
        } // END if
            
    } // END while

    return false;
}

/**
 *   Parse the Motorola @@Hb (Short position/message) report.
 */
void gpsParsePositionMessage()
{
    // Convert the binary stream into data elements.  We will scale to the desired units
    // as the values are used.
    gpsPosition.updateFlag = true;

    gpsPosition.month = gpsBuffer[0];
    gpsPosition.day = gpsBuffer[1];
    gpsPosition.year = ((uint16_t) gpsBuffer[2] << 8) | gpsBuffer[3];
    gpsPosition.hours = gpsBuffer[4];
    gpsPosition.minutes = gpsBuffer[5];
    gpsPosition.seconds = gpsBuffer[6];
    gpsPosition.latitude = ((int32) gpsBuffer[11] << 24) | ((int32) gpsBuffer[12] << 16) | ((int32) gpsBuffer[13] << 8) | (int32) gpsBuffer[14];
    gpsPosition.longitude = ((int32) gpsBuffer[15] << 24) | ((int32) gpsBuffer[16] << 16) | ((int32) gpsBuffer[17] << 8) | gpsBuffer[18];
    gpsPosition.altitudeCM = ((int32) gpsBuffer[19] << 24) | ((int32) gpsBuffer[20] << 16) | ((int32) gpsBuffer[21] << 8) | gpsBuffer[22];
    gpsPosition.altitudeFeet = gpsPosition.altitudeCM * 100l / 3048l;
    gpsPosition.vSpeed = ((uint16_t) gpsBuffer[27] << 8) | gpsBuffer[28];
    gpsPosition.hSpeed = ((uint16_t) gpsBuffer[29] << 8) | gpsBuffer[30];
    gpsPosition.heading = ((uint16_t) gpsBuffer[31] << 8) | gpsBuffer[32];
    gpsPosition.dop = ((uint16_t) gpsBuffer[33] << 8) | gpsBuffer[34];
    gpsPosition.visibleSats = gpsBuffer[35];
    gpsPosition.trackedSats = gpsBuffer[36];
    gpsPosition.status = ((uint16_t) gpsBuffer[37] << 8) | gpsBuffer[38];

    // Update the peak altitude if we have a valid 3D fix.
    if (gpsGetFixType() == GPS_3D_FIX)
        if (gpsPosition.altitudeFeet > gpsPeakAltitude)
            gpsPeakAltitude = gpsPosition.altitudeFeet;
}

/**
 *  Turn on the GPS engine power and serial interface.
 */
void gpsPowerOn()
{
    // 3.0 VDC LDO control line.
    output_high (IO_GPS_PWR);

    // Enable the UART and the transmit line.
#asm
    bsf 0xFAB.7
#endasm
}

/**
 *   Turn off the GPS engine power and serial interface.
 */
void gpsPowerOff()
{
    // Disable the UART and the transmit line.
#asm
    bcf 0xFAB.7
#endasm

    // 3.0 VDC LDO control line.
    output_low (IO_GPS_PWR);
}

/**
 *   Read the serial FIFO and process complete GPS messages.
 */
void gpsUpdate() 
{
    uint8_t value;

    // This state machine handles each characters as it is read from the GPS serial port.
    // We are looking for the GPS mesage @@Hb ... C
    while (serialHasData()) 
    {
        // Get the character value.
        value = serialRead();

        // Process based on the state machine.
        switch (gpsParseState) 
        {
            case GPS_START1:
                if (value == '@')
                    gpsParseState = GPS_START2;
                break;

            case GPS_START2:
                if (value == '@')
                    gpsParseState = GPS_COMMAND1;
                else
                    gpsParseState = GPS_START1;
                break;

            case GPS_COMMAND1:
                if (value == 'H')
                    gpsParseState = GPS_COMMAND2;
                else
                    gpsParseState = GPS_START1;
                break;

            case GPS_COMMAND2:
                if (value == 'b') 
                {
                    gpsParseState = GPS_READMESSAGE;
                    gpsIndex = 0;
                    gpsChecksum = 0;
                    gpsChecksum ^= 'H';
                    gpsChecksum ^= 'b';
                } else
                    gpsParseState = GPS_START1;
                break;

            case GPS_READMESSAGE:
                gpsChecksum ^= value;
                gpsBuffer[gpsIndex++] = value;

                if (gpsIndex == 47)
                    gpsParseState = GPS_CHECKSUMMESSAGE;

                break;

            case GPS_CHECKSUMMESSAGE:
                if (gpsChecksum == value)
                    gpsParseState = GPS_EOMCR;
                else
                    gpsParseState = GPS_START1;
                break;

            case GPS_EOMCR:
                if (value == 13)
                    gpsParseState = GPS_EOMLF;
                else
                    gpsParseState = GPS_START1;
                break;

            case GPS_EOMLF:
                // Once we have the last character, convert the binary message to something usable.
                if (value == 10)
                    gpsParsePositionMessage();

                gpsParseState = GPS_START1;
                break;
        } // END switch
    } // END while
}

/** @} */


/**
 *  @defgroup log Flight Data Recorder
 *
 *  Functions to manage and control the flight data recorder
 *
 *  @{
 */

/// Number of bytes to buffer before writing to flash memory.
#define LOG_WRITE_BUFFER_SIZE 40

/// Last used address in flash memory.
uint32_t logAddress;

/// Temporary buffer that holds data before it is written to flash device.
uint8_t logBuffer[LOG_WRITE_BUFFER_SIZE];

/// Current index into log buffer.
uint8_t logIndex;

/** 
 *    Last used address in flash memory.  This location is where the next log data will
 *    be written.
 *
 *    @return 24-bit flash memory address
 */
uint32_t logGetAddress()
{
    return logAddress;
}

/**
 *   Write the contents of the temporary log buffer to the flash device.  If the buffer
 *   is empty, nothing is done.
 */
void logFlush()
{
    // We only need to write if there is data.
    if (logIndex != 0) 
    {
        flashWriteBlock (logAddress, logBuffer, logIndex);
        logAddress += logIndex;
        logIndex = 0;
    } // END if
}

/** 
 *   Prepare the flight data recorder for logging.
 */
void logInit()
{
    uint8_t buffer[8];
    bool_t endFound;

    fprintf (PC_HOST, "Searching for end of flash log...");

    logAddress = 0x0000;
    endFound = false;

    // Read each logged data block from flash to determine how long it is.
    do 
    {
        // Read the data log entry type.
        flashReadBlock (logAddress, buffer, 1);

        // Based on the log entry type, we'll skip over the data contained in the entry.
        switch (buffer[0]) 
        {
            case LOG_BOOTED:
                logAddress += 7;
                break;

            case LOG_COORD:
                logAddress += 26;
                break;

            case LOG_TEMPERATURE:
                logAddress += 3;
                break;

            case LOG_VOLTAGE:
                logAddress += 5;
                break;

            case 0xff:
                endFound = true;
                break;

            default:
                ++logAddress;
        } // END switch
    } while (logAddress < 0x100000 && !endFound);

    fprintf (PC_HOST, "done.  Log contains %ld bytes.\n\r", logAddress);

    logIndex = 0;
}

/**
 *   Start a entry in the data log.
 *
 *   @param type of log entry, i.e. LOG_BOOTED, LOG_COORD, etc.
 */
void logType (LOG_TYPE type)
{
    // Only add the new entry if there is space.
    if (logAddress >= 0x100000)
        return;

    // Write the old entry first.
    logFlush();

    // Save the type and set the log buffer pointer.
    logBuffer[0] = type;
    logIndex = 1;
}

/**
 *  Save an unsigned, 8-bit value in the log.
 *
 *  @param value unsigned, 8-bit value
 */
void logUint8 (uint8_t value)
{
    logBuffer[logIndex++] = value;
}

/**
 *  Save a signed, 16-bit value in the log.
 *
 *  @param value signed, 16-bit value
 */
void logInt16 (int16_t value)
{
    logBuffer[logIndex++] = (value >> 8) & 0xff;
    logBuffer[logIndex++] = value & 0xff;
}

/**
 *  Save an unsigned, 16-bit value in the log.
 *
 *  @param value unsigned, 16-bit value
 */
void logUint16 (uint16_t value)
{
    logBuffer[logIndex++] = (value >> 8) & 0xff;
    logBuffer[logIndex++] = value & 0xff;
}

/**
 *  Save a signed, 32-bit value in the log.
 *
 *  @param value signed, 32-bit value
 */
void logInt32 (int32_t value)
{
    logBuffer[logIndex++] = (value >> 24) & 0xff;
    logBuffer[logIndex++] = (value >> 16) & 0xff;
    logBuffer[logIndex++] = (value >> 8) & 0xff;
    logBuffer[logIndex++] = value & 0xff;
}

/** @} */

/**
 *  @defgroup LM92 LM92 temperature sensor
 *
 *  Read and control the National Semiconductor LM92 I2C temperature sensor
 *
 *  @{
 */

/** 
 *   Read the LM92 temperature value in 0.1 degrees F.
 *
 *   @return 0.1 degrees F
 */
int16_t lm92GetTemp()
{
    int16_t value;
    int32_t temp;

    // Set the SDA and SCL to input pins to control the LM92.
    set_tris_c (0x9a);

    // Read the temperature register value.
    i2c_start();
    i2c_write(0x97);
    value = ((int16_t) i2c_read() << 8);
    value = value | ((int16_t) i2c_read() & 0x00f8);
    i2c_stop();

    // Set the SDA and SCL back to outputs for use with the AD9954 because we share common clock pins.
    set_tris_c (0x82);

    //  LM92 register   0.0625degC/bit   9   10     9
    //  ------------- * -------------- * - * -- =  -- + 320
    //        8                          5         64

    // Convert to degrees F.
    temp = (int32_t) value;
    temp = ((temp * 9l) / 64l) + 320;
    
    return (int16_t) temp;
}

/** @} */


/**
 *  @defgroup serial Serial Port FIFO
 *
 *  FIFO for the built-in serial port.
 *
 *  @{
 */

/// Size of serial port FIFO in bytes.  It must be a power of 2, i.e. 2, 4, 8, 16, etc.
#define SERIAL_BUFFER_SIZE 64

/// Mask to wrap around at end of circular buffer.  (SERIAL_BUFFER_SIZE - 1)
#define SERIAL_BUFFER_MASK 0x3f

/// Index to the next free location in the buffer.
uint8_t serialHead;

/// Index to the next oldest data in the buffer.
uint8_t serialTail;

/// Circular buffer (FIFO) to hold serial data.
uint8_t serialBuffer[SERIAL_BUFFER_SIZE];

/**
 *   Determine if the FIFO contains data.
 *
 *   @return true if data present; otherwise false
 */
bool_t serialHasData()
{
    if (serialHead == serialTail)
        return false;

    return true;
}

/** 
 *   Initialize the serial processor.
 */
void serialInit()
{
    serialHead = 0;
    serialTail = 0;
}

/**
 *   Get the oldest character from the FIFO.
 *
 *   @return oldest character; 0 if FIFO is empty
 */
uint8_t serialRead()
{
    uint8_t value;

    // Make sure we have something to return.
    if (serialHead == serialTail)
        return 0;

    // Save the value.
    value = serialBuffer[serialTail];

    // Update the pointer.
    serialTail = (serialTail + 1) & SERIAL_BUFFER_MASK;

    return value;
}

/**
 *   Read and store any characters in the PIC serial port in a FIFO.
 */
void serialUpdate()
{
    // If there isn't a character in the PIC buffer, just leave.
    while (kbhit()) 
    {
        // Save the value in the FIFO.
        serialBuffer[serialHead] = getc();

        // Move the pointer to the next open space.
        serialHead = (serialHead + 1) & SERIAL_BUFFER_MASK;
    }
}

/** @} */

/**
 *  @defgroup sys System Library Functions
 *
 *  Generic system functions similiar to the run-time C library.
 *
 *  @{
 */

/**
 *    Calculate the CRC-16 CCITT of buffer that is length bytes long.
 *    The crc parameter allow the calculation on the CRC on multiple buffers.
 *
 *    @param buffer Pointer to data buffer.
 *    @param length number of bytes in data buffer
 *    @param crc starting value
 *
 *    @return CRC-16 of buffer[0 .. length]
 */
uint16_t sysCRC16(uint8_t *buffer, uint8_t length, uint16_t crc)
{
    uint8_t i, bit, value;

    for (i = 0; i < length; ++i) 
    {
        value = buffer[i];

        for (bit = 0; bit < 8; ++bit) 
        {
            crc ^= (value & 0x01);
            crc = ( crc & 0x01 ) ? ( crc >> 1 ) ^ 0x8408 : ( crc >> 1 );
            value = value >> 1;
        } // END for
    } // END for

    return crc ^ 0xffff;
}

/**
 *   Initialize the system library and global resources.
 */
void sysInit()
{
    gpsPowerOff ();
    output_high (IO_LED);

    output_high (IO_CS);
    output_low (IO_PS1);
    output_low (IO_PS0);
    output_low (IO_OSK);
    output_low (IO_UPDATE);
    output_low (IO_PTT);
    output_low (IO_GPS_TXD);

    // Configure the port direction (input/output).
    set_tris_a (0xc3);
    set_tris_b (0x44);
    set_tris_c (0x82);

    // Display a startup message during boot.
    fprintf (PC_HOST, "System booted.\n\r");
}

/**
 *   Log the current GPS position.
 */
void sysLogGPSData()
{
    // Log the data.
    logType (LOG_COORD);
    logUint8 (gpsPosition.hours);
    logUint8 (gpsPosition.minutes);
    logUint8 (gpsPosition.seconds);
    logInt32 (gpsPosition.latitude);
    logInt32 (gpsPosition.longitude);
    logInt32 (gpsPosition.altitudeCM);

    logUint16 (gpsPosition.vSpeed);
    logUint16 (gpsPosition.hSpeed);
    logUint16 (gpsPosition.heading);

    logUint16 (gpsPosition.status);

    logUint8 ((uint8_t) (gpsPosition.dop & 0xff));
    logUint8 ((uint8_t) ((gpsPosition.visibleSats << 4) | gpsPosition.trackedSats));
}

/**
 *   Log the ADC values of the bus and reference voltage values.
 */
void sysLogVoltage()
{
    logType (LOG_VOLTAGE);
    logUint16 (adcRawBusVolt());
    logUint16 (adcRawRefVolt());
}

/** @} */

/**
 *  @defgroup rtc Real Time Interrupt tick
 *
 *  Manage the built-in real time interrupt.  The interrupt clock PRI is 104uS (9600 bps).
 *
 *  @{
 */

/// A counter that ticks every 100mS.
uint8_t timeTicks;

/// Counts the number of 104uS interrupts for a 100mS time period.
uint16_t timeInterruptCount;

/// Counts the number of 100mS time periods in 1 second.
uint8_t time100ms;

/// System time in seconds.
uint8_t timeSeconds;

/// System time in minutes.
uint8_t timeMinutes;

/// System time in hours.
uint8_t timeHours;

/// Desired LED duty cycle 0 to 9 where 0 = 0% and 9 = 90%.
uint8_t timeDutyCycle;

/// Current value of the timer 1 compare register used to generate 104uS interrupt rate (9600bps).
uint16_t timeCompare;

/// 16-bit NCO where the upper 8-bits are used to index into the frequency generation table.
uint16_t timeNCO;

/// Audio tone NCO update step (phase).
uint16_t timeNCOFreq;

/// Counter used to deciminate down from the 104uS to 833uS interrupt rate.  (9600 to 1200 baud) 
uint8_t timeLowRateCount;

/// Current TNC mode (standby, 1200bps A-FSK, or 9600bps FSK)
TNC_DATA_MODE tncDataMode;

/// Flag set true once per second.
bool_t timeUpdateFlag;

/// Flag that indicate the flight time should run.
bool_t timeRunFlag;

/// The change in the CCP_1 register for each 104uS (9600bps) interrupt period.
#define TIME_RATE 125

/**
 *   Running 8-bit counter that ticks every 100mS.
 *
 *   @return 100mS time tick
 */
uint8_t timeGetTicks()
{
    return timeTicks;
}

/**
 *   Initialize the real-time clock.
 */
void timeInit()
{
    timeTicks = 0;
    timeInterruptCount = 0;
    time100mS = 0;
    timeSeconds = 0;
    timeMinutes = 0;
    timeHours = 0;
    timeDutyCycle = TIME_DUTYCYCLE_70;
    timeCompare = TIME_RATE;
    timeUpdateFlag = false;
    timeNCO = 0x00;
    timeLowRateCount = 0;
    timeNCOFreq = 0x2000;
    tncDataMode = TNC_MODE_STANDBY;  
    timeRunFlag = false;
    
    // Configure CCP1 to interrupt at 1mS for PSK31 or 833uS for 1200 baud APRS
    CCP_1 = TIME_RATE;
    set_timer1(timeCompare);
    setup_ccp1( CCP_COMPARE_INT );
    setup_timer_1( T1_INTERNAL | T1_DIV_BY_4 );
}

/**
 *   Function return true once a second based on real-time clock.
 *
 *   @return true on one second tick; otherwise false
 */
bool_t timeIsUpdate()
{
    if (timeUpdateFlag) 
    {
        timeUpdateFlag = false;
        return true;
    } // END if

    return false;
}

/**
 *   Set the blink duty cycle of the heartbeat LED.  The LED blinks at a 1Hz rate.
 *
 *   @param dutyCycle TIME_DUTYCYCLE_xx constant
 */
void timeSetDutyCycle (uint8_t dutyCycle)
{
    timeDutyCycle = dutyCycle;
}

/**
 *   Set a flag to indicate the flight time should run.  This flag is typically set when the payload
 *   lifts off.
 */
void timeSetRunFlag()
{
    timeRunFlag = true;
}

#INT_CCP1
/**
 *   Timer interrupt handler called every 104uS (9600 times/second).
 */
void timeUpdate()
{
    // Setup the next interrupt for the operational mode.
    timeCompare += TIME_RATE;
    CCP_1 = timeCompare;

    switch (tncDataMode) 
    {
        case TNC_MODE_STANDBY:
            break;

        case TNC_MODE_1200_AFSK:
            ddsSetFTW (freqTable[timeNCO >> 8]);

            timeNCO += timeNCOFreq;

            if (++timeLowRateCount == 8) 
            {
                timeLowRateCount = 0;
                tnc1200TimerTick();
            } // END if
            break;

        case TNC_MODE_9600_FSK:
            tnc9600TimerTick();
            break;
    } // END switch

    // Read the GPS serial port and save any incoming characters.
    serialUpdate();

    // Count the number of milliseconds required for the tenth second counter.
    if (++timeInterruptCount == 960) 
    {
        timeInterruptCount = 0;

        // This timer just ticks every 100mS and is used for general timing.
        ++timeTicks;

        // Roll the counter over every second.
        if (++time100mS == 10) 
        {
            time100mS = 0;

            // We set this flag true every second.
            timeUpdateFlag = true;

            // Maintain a Real Time Clock.
            if (timeRunFlag)
                if (++timeSeconds == 60) 
                {
                    timeSeconds = 0;
    
                    if (++timeMinutes == 60) 
                    {
                        timeMinutes = 0;
                        ++timeHours;
                    } // END if timeMinutes
                } // END if timeSeconds
        } // END if time100mS

        // Flash the status LED at timeDutyCycle % per second.  We use the duty cycle for mode feedback.
        if (time100mS >= timeDutyCycle)
            output_low (IO_LED);
        else
            output_high (IO_LED);
    } // END if
}

/** @} */

/**
 *  @defgroup tnc TNC (Terminal Node Controller)
 *
 *  Functions that provide a subset of the TNC functions.
 *
 *  @{
 */

/// The number of start flag bytes to send before the packet message.  (360bits * 1200bps = 300mS)
#define TNC_TX_DELAY 45

/// The size of the TNC output buffer.
#define TNC_BUFFER_SIZE 80

/// States that define the current mode of the 1200 bps (A-FSK) state machine.
enum TNC_TX_1200BPS_STATE 
{
    /// Stand by state ready to accept new message.
    TNC_TX_READY,

    /// 0x7E bit stream pattern used to define start of APRS message.
    TNC_TX_SYNC,

    /// Transmit the AX.25 header that contains the source/destination call signs, APRS path, and flags.
    TNC_TX_HEADER,

    /// Transmit the message data.
    TNC_TX_DATA,

    /// Transmit the end flag sequence.
    TNC_TX_END
};

/// Enumeration of the messages we can transmit. 
enum TNC_MESSAGE_TYPE 
{
    /// Startup message that contains software version information.
    TNC_BOOT_MESSAGE,

    /// Plain text status message.
    TNC_STATUS,

    /// Message that contains GPS NMEA-0183 $GPGGA message.
    TNC_GGA,

    /// Message that contains GPS NMEA-0183 $GPRMC message.
    TNC_RMC
};

/// AX.25 compliant packet header that contains destination, station call sign, and path.
/// 0x76 for SSID-11, 0x78 for SSID-12
uint8_t TNC_AX25_HEADER[30] = { 
    'A' << 1, 'P' << 1, 'R' << 1, 'S' << 1, ' ' << 1, ' ' << 1, 0x60, \
    'K' << 1, 'D' << 1, '7' << 1, 'L' << 1, 'M' << 1, 'O' << 1, 0x76, \
    'G' << 1, 'A' << 1, 'T' << 1, 'E' << 1, ' ' << 1, ' ' << 1, 0x60, \
    'W' << 1, 'I' << 1, 'D' << 1, 'E' << 1, '3' << 1, ' ' << 1, 0x67, \
    0x03, 0xf0 };


/// The next bit to transmit.
uint8_t tncTxBit;

/// Current mode of the 1200 bps state machine.
TNC_TX_1200BPS_STATE tncMode;

/// Counter for each bit (0 - 7) that we are going to transmit.
uint8_t tncBitCount;

/// A shift register that holds the data byte as we bit shift it for transmit.
uint8_t tncShift;

/// Index into the APRS header and data array for each byte as we transmit it.
uint8_t tncIndex;

/// The number of bytes in the message portion of the AX.25 message.
uint8_t tncLength;

/// A copy of the last 5 bits we've transmitted to determine if we need to bit stuff on the next bit.
uint8_t tncBitStuff;

/// Pointer to TNC buffer as we save each byte during message preparation.
uint8_t *tncBufferPnt;

/// The type of message to tranmit in the next packet.
TNC_MESSAGE_TYPE tncPacketType;

/// Buffer to hold the message portion of the AX.25 packet as we prepare it.
uint8_t tncBuffer[TNC_BUFFER_SIZE];

/// Flag that indicates we want to transmit every 5 seconds.
bool_t tncHighRateFlag;

/** 
 *   Initialize the TNC internal variables.
 */
void tncInit()
{
    tncTxBit = 0;
    tncMode = TNC_TX_READY;
    tncPacketType = TNC_BOOT_MESSAGE;
    tncHighRateFlag = false;
}

/**
 *  Determine if the hardware if ready to transmit a 1200 baud packet.
 *
 *  @return true if ready; otherwise false
 */
bool_t tncIsFree()
{
    if (tncMode == TNC_TX_READY)
        return true;

    return false;
}

void tncHighRate(bool_t state)
{
    tncHighRateFlag = state;
}

/**
 *   Configure the TNC for the desired data mode.
 *
 *    @param dataMode enumerated type that specifies 1200bps A-FSK or 9600bps FSK
 */ 
void tncSetMode(TNC_DATA_MODE dataMode)
{
    switch (dataMode) 
    {
        case TNC_MODE_1200_AFSK:
            ddsSetMode (DDS_MODE_AFSK);
            break;

        case TNC_MODE_9600_FSK:
            ddsSetMode (DDS_MODE_FSK);

            // FSK tones at 445.947 and 445.953 MHz
            ddsSetFSKFreq (955382980, 955453621);
            break;
    } // END switch

    tncDataMode = dataMode; 
}

/**
 *  Determine if the seconds value timeSeconds is a valid time slot to transmit
 *  a message.  Time seconds is in UTC.
 *
 *  @param timeSeconds UTC time in seconds
 *
 *  @return true if valid time slot; otherwise false
 */
bool_t tncIsTimeSlot (uint8_t timeSeconds)
{
    if (tncHighRateFlag)
    {
        if ((timeSeconds % 5) == 0)
            return true;

        return false;
    } // END if

    switch (timeSeconds) 
    {
        case 0:
        case 15:
        case 30:
        case 45:
            return true;

        default:
            return false;
    } // END switch
}

/**
 *   Method that is called every 833uS to transmit the 1200bps A-FSK data stream.
 *   The provides the pre and postamble as well as the bit stuffed data stream.
 */
void tnc1200TimerTick()
{
    // Set the A-FSK frequency.
    if (tncTxBit == 0x00)
        timeNCOFreq = 0x2000;
    else
        timeNCOFreq = 0x3aab;

    switch (tncMode) 
    {
        case TNC_TX_READY:
            // Generate a test signal alteranting between high and low tones.
            tncTxBit = (tncTxBit == 0 ? 1 : 0);
            break;

        case TNC_TX_SYNC:
            // The variable tncShift contains the lastest data byte.
            // NRZI enocde the data stream.
            if ((tncShift & 0x01) == 0x00)
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;
                    
            // When the flag is done, determine if we need to send more or data.
            if (++tncBitCount == 8) 
            {
                tncBitCount = 0;
                tncShift = 0x7e;

                // Once we transmit x mS of flags, send the data.
                // txDelay bytes * 8 bits/byte * 833uS/bit = x mS
                if (++tncIndex == TNC_TX_DELAY) 
                {
                    tncIndex = 0;
                    tncShift = TNC_AX25_HEADER[0];
                    tncBitStuff = 0;
                    tncMode = TNC_TX_HEADER;
                } // END if
            } else
                tncShift = tncShift >> 1;
            break;

        case TNC_TX_HEADER:
            // Determine if we have sent 5 ones in a row, if we have send a zero.
            if (tncBitStuff == 0x1f) 
            {
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;

                tncBitStuff = 0x00;
                return;
            }    // END if

            // The variable tncShift contains the lastest data byte.
            // NRZI enocde the data stream.
            if ((tncShift & 0x01) == 0x00)
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;

            // Save the data stream so we can determine if bit stuffing is 
            // required on the next bit time.
            tncBitStuff = ((tncBitStuff << 1) | (tncShift & 0x01)) & 0x1f;

            // If all the bits were shifted, get the next byte.
            if (++tncBitCount == 8) 
            {
                tncBitCount = 0;

                // After the header is sent, then send the data.
                if (++tncIndex == sizeof(TNC_AX25_HEADER)) 
                {
                    tncIndex = 0;
                    tncShift = tncBuffer[0];
                    tncMode = TNC_TX_DATA;
                } else
                    tncShift = TNC_AX25_HEADER[tncIndex];

            } else
                tncShift = tncShift >> 1;

            break;

        case TNC_TX_DATA:
            // Determine if we have sent 5 ones in a row, if we have send a zero.
            if (tncBitStuff == 0x1f) 
            {
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;

                tncBitStuff = 0x00;
                return;
            }    // END if

            // The variable tncShift contains the lastest data byte.
            // NRZI enocde the data stream.
            if ((tncShift & 0x01) == 0x00)
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;

            // Save the data stream so we can determine if bit stuffing is 
            // required on the next bit time.
            tncBitStuff = ((tncBitStuff << 1) | (tncShift & 0x01)) & 0x1f;

            // If all the bits were shifted, get the next byte.
            if (++tncBitCount == 8) 
            {
                tncBitCount = 0;

                // If everything was sent, transmit closing flags.
                if (++tncIndex == tncLength) 
                {
                    tncIndex = 0;
                    tncShift = 0x7e;
                    tncMode = TNC_TX_END;
                } else
                    tncShift = tncBuffer[tncIndex];

            } else
                tncShift = tncShift >> 1;

            break;

        case TNC_TX_END:
            // The variable tncShift contains the lastest data byte.
            // NRZI enocde the data stream. 
            if ((tncShift & 0x01) == 0x00)
                if (tncTxBit == 0)
                    tncTxBit = 1;
                else
                    tncTxBit = 0;

            // If all the bits were shifted, get the next one.
            if (++tncBitCount == 8) 
            {
                tncBitCount = 0;
                tncShift = 0x7e;
    
                // Transmit two closing flags.
                if (++tncIndex == 2) 
                {
                    tncMode = TNC_TX_READY;

                    // Tell the TNC time interrupt to stop generating the frequency words.
                    tncDataMode = TNC_MODE_STANDBY;

                    // Key off the DDS.
                    output_low (IO_OSK);
                    output_low (IO_PTT);
                    ddsSetMode (DDS_MODE_POWERDOWN);

                    return;
                } // END if
            } else
                tncShift = tncShift >> 1;

            break;
    } // END switch
}

/**
 *   Method that is called every 104uS to transmit the 9600bps FSK data stream.
 */
void tnc9600TimerTick()
{

}

/**
 *    Write character to the TNC buffer.  Maintain the pointer
 *    and length to the buffer.  The pointer tncBufferPnt and tncLength
 *    must be set before calling this function for the first time.
 * 
 *    @param character to save to telemetry buffer
 */
void tncTxByte (uint8_t character)
{
    *tncBufferPnt++ = character;
    ++tncLength;
}

/**
 *   Generate the GPS NMEA standard UTC time stamp.  Data is written through the tncTxByte
 *   callback function.
 */
void tncNMEATime()
{
    // UTC of position fix.
    printf (tncTxByte, "%02d%02d%02d,", gpsPosition.hours, gpsPosition.minutes, gpsPosition.seconds);
}

/**
 *   Generate the GPS NMEA standard latitude/longitude fix.  Data is written through the tncTxByte
 *   callback function.
 */
void tncNMEAFix()
{
    uint8_t dirChar;
    uint32_t coord, coordMin;

    // Latitude value.
    coord = gpsPosition.latitude;

    if (gpsPosition.latitude < 0) 
    {
        coord = gpsPosition.latitude * -1;
        dirChar = 'S';
    } else {
        coord = gpsPosition.latitude;
        dirChar = 'N';
    }

    coordMin = (coord % 3600000) / 6;
    printf (tncTxByte, "%02ld%02ld.%04ld,%c,", (uint32_t) (coord / 3600000), (uint32_t) (coordMin / 10000), (uint32_t) (coordMin % 10000), dirChar);


    // Longitude value.
    if (gpsPosition.longitude < 0) 
    {
        coord = gpsPosition.longitude * - 1;
        dirChar = 'W';
    } else {
        coord = gpsPosition.longitude;
        dirChar = 'E';
    }

    coordMin = (coord % 3600000) / 6;
    printf (tncTxByte, "%03ld%02ld.%04ld,%c,", (uint32_t) (coord / 3600000), (uint32_t) (coordMin / 10000), (uint32_t) (coordMin % 10000), dirChar);

}

/**
 *   Generate the GPS NMEA-0183 $GPGGA packet.  Data is written through the tncTxByte
 *   callback function.
 */
void tncGPGGAPacket()
{
    // Generate the GPGGA message.
    printf (tncTxByte, "$GPGGA,");

    // Standard NMEA time.
    tncNMEATime();

    // Standard NMEA-0183 latitude/longitude.
    tncNMEAFix();

    // GPS status where 0: not available, 1: available
    if (gpsGetFixType() != GPS_NO_FIX)
        printf (tncTxByte, "1,");
    else
        printf (tncTxByte, "0,");

    // Number of visible birds.
    printf (tncTxByte, "%02d,", gpsPosition.trackedSats);

    // DOP
    printf (tncTxByte, "%ld.%01ld,", gpsPosition.dop / 10, gpsPosition.dop % 10);

    // Altitude in meters.
    printf (tncTxByte, "%ld.%02ld,M,,M,,", (int32_t) (gpsPosition.altitudeCM / 100l), (int32_t) (gpsPosition.altitudeCM % 100));

    // Checksum, we add 1 to skip over the $ character.
    printf (tncTxByte, "*%02X", gpsNMEAChecksum(tncBuffer + 1, tncLength - 1));
}

/**
 *   Generate the GPS NMEA-0183 $GPRMC packet.  Data is written through the tncTxByte
 *   callback function.
 */
void tncGPRMCPacket()
{
    uint32_t temp;

    // Generate the GPRMC message.
    printf (tncTxByte, "$GPRMC,");

    // Standard NMEA time.
    tncNMEATime();

    // GPS status.
    if (gpsGetFixType() != GPS_NO_FIX)
        printf (tncTxByte, "A,");
    else
        printf (tncTxByte, "V,");

    // Standard NMEA-0183 latitude/longitude.
    tncNMEAFix();

    // Speed knots and heading.
    temp = (int32_t) gpsPosition.hSpeed * 75000 / 385826;
    printf (tncTxByte, "%ld.%ld,%ld.%ld,", (int16_t) (temp / 10), (int16_t) (temp % 10), gpsPosition.heading / 10, gpsPosition.heading % 10);

    // Date
    printf (tncTxByte, "%02d%02d%02ld,,", gpsPosition.day, gpsPosition.month, gpsPosition.year % 100);

    // Checksum, skip over the $ character.
    printf (tncTxByte, "*%02X", gpsNMEAChecksum(tncBuffer + 1, tncLength - 1));
}

/**
 *   Generate the plain text status packet.  Data is written through the tncTxByte
 *   callback function.
 */
void tncStatusPacket(int16_t temperature)
{
    uint16_t voltage;

    // Plain text telemetry.
    printf (tncTxByte, ">ANSR ");
    
    // Display the flight time.
    printf (tncTxByte, "%02U:%02U:%02U ", timeHours, timeMinutes, timeSeconds);
    
    // Altitude in feet.
    printf (tncTxByte, "%ld' ", gpsPosition.altitudeFeet);
    
    // Peak altitude in feet.
    printf (tncTxByte, "%ld'pk ", gpsGetPeakAltitude());
    
    // GPS hdop or pdop
    printf (tncTxByte, "%lu.%lu", gpsPosition.dop / 10, gpsPosition.dop % 10);

    // The text 'pdop' for a 3D fix, 'hdop' for a 2D fix, and 'dop' for no fix.
    switch (gpsGetFixType()) 
    {
        case GPS_NO_FIX:
            printf (tncTxByte, "dop ");
            break;

        case GPS_2D_FIX:
            printf (tncTxByte, "hdop ");
            break;


        case GPS_3D_FIX:
            printf (tncTxByte, "pdop ");
            break;
    } // END switch

    // Number of satellites in the solution.
    printf (tncTxByte, "%utrk ", gpsPosition.trackedSats);
    
    // Display main bus voltage.
    voltage = adcGetMainBusVolt();
    printf (tncTxByte, "%lu.%02luvdc ", voltage / 100, voltage % 100);
    
    // Display internal temperature.
    printf (tncTxByte, "%ld.%01ldF ", temperature / 10, abs(temperature % 10));
    
    // Print web address link.
    printf (tncTxByte, "www.kd7lmo.net");
}  

/** 
 *    Prepare an AX.25 data packet.  Each time this method is called, it automatically
 *    rotates through 1 of 3 messages.
 *
 *    @param dataMode enumerated type that specifies 1200bps A-FSK or 9600bps FSK
 */
void tncTxPacket(TNC_DATA_MODE dataMode)
{
    int16_t temperature;
    uint16_t crc;

    // Only transmit if there is not another message in progress.
    if (tncMode != TNC_TX_READY)
        return;

    // Log the battery and reference voltage before we start the RF chain.
    sysLogVoltage();

    // We need to read the temperature sensor before we setup the DDS since they share a common clock pin.
    temperature = lm92GetTemp();

    // Log the system temperature every time we transmit a packet.
    logType (LOG_TEMPERATURE);
    logInt16 (temperature);

    // Configure the DDS for the desired operational.
    tncSetMode (dataMode);

    // Set a pointer to our TNC output buffer.
    tncBufferPnt = tncBuffer;

    // Set the message length counter.
    tncLength = 0;

    // Determine the contents of the packet.
    switch (tncPacketType) 
    {
        case TNC_BOOT_MESSAGE:
            printf (tncTxByte, ">ANSR Pico Beacon - V3.05");

            // Select the next packet we will generate.
            tncPacketType = TNC_STATUS;
            break;

        case TNC_STATUS:
            tncStatusPacket(temperature);

            // Select the next packet we will generate.
            tncPacketType = TNC_GGA;
            break;

        case TNC_GGA:
            tncGPGGAPacket();

            // Select the next packet we will generate.
            tncPacketType = TNC_RMC;
            break;

        case TNC_RMC:
            tncGPRMCPacket();

            // Select the next packet we will generate.
            tncPacketType = TNC_STATUS;
            break;
    }

    // Add the end of message character.
    printf (tncTxByte, "\015");

    // Calculate the CRC for the header and message.
    crc = sysCRC16(TNC_AX25_HEADER, sizeof(TNC_AX25_HEADER), 0xffff);
    crc = sysCRC16(tncBuffer, tncLength, crc ^ 0xffff);

    // Save the CRC in the message.
    *tncBufferPnt++ = crc & 0xff;
    *tncBufferPnt = (crc >> 8) & 0xff;

    // Update the length to include the CRC bytes.
    tncLength += 2;

    // Prepare the variables that are used in the real-time clock interrupt.
    tncBitCount = 0;
    tncShift = 0x7e;
    tncTxBit = 0;
    tncIndex = 0;
    tncMode = TNC_TX_SYNC;

    // Turn on the PA chain.
    output_high (IO_PTT);

    // Wait for the PA chain to power up.
    delay_ms (10);

    // Key the DDS.
    output_high (IO_OSK);

    // Log the battery and reference voltage just after we key the transmitter.
    sysLogVoltage();
}

/** @} */

uint32_t counter;

uint8_t bitIndex;
uint8_t streamIndex;
uint8_t value;

uint8_t bitStream[] = { 0x10, 0x20, 0x30 };

void init()
{
    counter = 0;
    bitIndex = 0;
    streamIndex = 0;
    value = bitStream[0];
}

void test()
{
    counter += 0x10622d;

    CCP_1 = (uint16_t) ((counter >> 16) & 0xffff);

    if ((value & 0x80) == 0x80)
        setup_ccp1 (CCP_COMPARE_SET_ON_MATCH);
    else
        setup_ccp1 (CCP_COMPARE_CLR_ON_MATCH);

    if (++bitIndex == 8)
    {
        bitIndex = 0;
        
        if (++streamIndex == sizeof(bitStream))
        {
            streamIndex = 0;
        }

        value = bitStream[streamIndex];
    } else
        value = value << 1;
}

// This is where we go after reset.
void main()
{
    uint8_t i, utcSeconds, lockLostCounter;

test();

    // Configure the basic systems.
    sysInit();

    // Wait for the power converter chains to stabilize.
    delay_ms (100);

    // Setup the subsystems.
    adcInit();
    flashInit();
    gpsInit();
    logInit();
    timeInit();
    serialInit();
    tncInit();

    // Program the DDS.
    ddsInit();

    // Turn off the LED after everything is configured.
    output_low (IO_LED);

    // Check for the diagnostics plug, otherwise we'll continue to boot.
    diagPort();

    // Setup our interrupts.
    enable_interrupts(GLOBAL);
    enable_interrupts(INT_CCP1);

    // Turn on the GPS engine.
    gpsPowerOn();

    // Allow the GPS engine to boot.
    delay_ms (250);

    // Initialize the GPS engine.
    while (!gpsSetup());

    // Charge the ADC filters.
    for (i = 0; i < 32; ++i)
        adcUpdate();

    // Log startup event.
    logType (LOG_BOOTED);
    logUint8 (gpsPosition.month);
    logUint8 (gpsPosition.day);
    logUint8 (gpsPosition.year & 0xff);

    logUint8 (gpsPosition.hours);
    logUint8 (gpsPosition.minutes);
    logUint8 (gpsPosition.seconds);

    // Transmit software version packet on start up.
    tncTxPacket(TNC_MODE_1200_AFSK);

    // Counters to send packets if the GPS time stamp is not available.
    lockLostCounter = 5;
    utcSeconds = 55;
  
    // This is the main loop that process GPS data and waits for the once per second timer tick.
    for (;;) 
    {
        // Read the GPS engine serial port FIFO and process the GPS data.
        gpsUpdate();

        if (gpsIsReady()) 
        {
            // Start the flight timer when we get a valid 3D fix.
            if (gpsGetFixType() == GPS_3D_FIX)
                timeSetRunFlag();

            // Generate our packets based on the GPS time.
            if (tncIsTimeSlot(gpsPosition.seconds))
                 tncTxPacket(TNC_MODE_1200_AFSK);

            // Sync the internal clock to GPS UTC time.
            utcSeconds = gpsPosition.seconds;

            // This counter is reset every time we receive the GPS message.
            lockLostCounter = 0;

            // Log the data to flash.
            sysLogGPSData();            
        } // END if gpsIsReady   

        // Processing that occurs once a second.
        if (timeIsUpdate()) 
        {
            // We maintain the UTC time in seconds if we shut off the GPS engine or it fails.
            if (++utcSeconds == 60)
                utcSeconds = 0;

            // If we loose information for more than 5 seconds, 
            // we will determine when to send a packet based on internal time.
            if (lockLostCounter == 5) 
            {
                if (tncIsTimeSlot(utcSeconds))
                    tncTxPacket(TNC_MODE_1200_AFSK);
            } else
                ++lockLostCounter;

            // Update the ADC filters.
            adcUpdate();

            if (timeHours == 5 && timeMinutes == 0 && timeSeconds == 0)
                gpsPowerOff();

        } // END if timeIsUpdate

    } // END for
}