Colony

/**

 * Copyright (c) 2009 Colony Project

 *

 * Permission is hereby granted, free of charge, to any person

 * obtaining a copy of this software and associated documentation

 * files (the "Software"), to deal in the Software without

 * restriction, including without limitation the rights to use,

 * copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following

 * conditions:

 *

 * The above copyright notice and this permission notice shall be

 * included in all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES

 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT

 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,

 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

 * OTHER DEALINGS IN THE SOFTWARE.

 **/

/**

 * @file xbee.c

 * @brief XBee Interface

 *

 * Implementation of low level communication with the XBee in API mode.

 *

 * @author Colony Project, CMU Robotics Club

 **/

#include "xbee.h"

#include "wl_defs.h"

#include <time.h>

// TODO: separate robot and computer code into two xbee.c files

#ifndef ROBOT

#include <fcntl.h>

#include <unistd.h>

#include <pthread.h>

#include <errno.h>

#include <termios.h>

#else

#include <serial.h> // TODO: integrate serial xbee functions into this file

#include <avr/interrupt.h>

#endif

// TODO: do we really need stdio and stdlib in the robot code?

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

/**@addtogroup xbee

 * @{ **/

/**@defgroup xbee_const xbee constants 

 * @{ **/

// TODO: move constants to xbee.h so they can be used publicly

/**@brief The port to use the XBee from on the computer. **/

#ifndef ROBOT

#define XBEE_PORT_DEFAULT "/dev/ttyUSB1"

#endif

/**@name xbee options

 * @{ **/

/**@brief Unset PAN, uses XBee default **/

#define XBEE_PAN_DEFAULT 0xFFFF

/**@brief Unset channel, uses XBee default **/

#define XBEE_CHANNEL_DEFAULT 0

/**@brief Broadcast to all robots in the PAN **/

#define XBEE_BROADCAST 0xFFFF

/**@brief No special options **/

#define XBEE_OPTIONS_NONE 0x00

/**@brief Do not receive a TX_STATUS message from this packet **/

#define XBEE_OPTIONS_DISABLE_RESPONSE 0x01

/**@brief Send the packet to all PANS **/

#define XBEE_OPTIONS_BROADCAST_ALL_PANS 0x04

/**@brief A transmit status packet **/

#define XBEE_TX_STATUS 0x89

/**@brief A packet received from another XBee **/

#define XBEE_RX 0x81

/**@}

 * @name xbee frame types

 * @{ **/

// TODO: add comments for all of these definitions

#define XBEE_FRAME_START 0x7E

#define XBEE_GET_PACKET_TIMEOUT 1000

/*Frame Types*/

#define XBEE_FRAME_STATUS 0x8A

#define XBEE_FRAME_AT_COMMAND 0x08

#define XBEE_FRAME_AT_COMMAND_RESPONSE 0x88

#define XBEE_FRAME_TX_REQUEST_64 0x00

#define XBEE_FRAME_TX_REQUEST_16 0x01

#define XBEE_FRAME_TX_STATUS XBEE_TX_STATUS

#define XBEE_FRAME_RX_64 0x80

#define XBEE_FRAME_RX_16 XBEE_RX

/** @} **/

// TODO: is this a good size?

/*Buffer sizes*/

#define XBEE_BUFFER_SIZE        128

#define PACKET_BUFFER_SIZE        108

/**@} **/ // end const group

/*Internal Function Prototypes*/

// TODO: convert all int references to int16_t syntax (see stdint.h)

/*I/O Functions*/

static int xbee_send(char* buf, int size);

static int xbee_send_string(char* c);

#ifndef ROBOT

static int xbee_read(char* buf, int size);

#endif

/*Command Mode Functions

 * Called during initialization.

 */

static int xbee_enter_command_mode(void);

static int xbee_exit_command_mode(void);

static int xbee_enter_api_mode(void);

static int xbee_exit_api_mode(void);

static int xbee_wait_for_string(char* s, int len);

static int xbee_wait_for_ok(void);

/*API Mode Functions*/

static int xbee_handle_packet(char* packet, int len);

static int xbee_handle_at_command_response(char* command, char result, char* extra, int extraLen);

static void xbee_handle_status(char status);

static int xbee_verify_checksum(char* packet, int len);

static char xbee_compute_checksum(char* packet, int len);

static int xbee_send_frame(char* buf, int len);

int xbee_send_read_at_command(char* command);

static int xbee_send_modify_at_command(char* command, char* value);

/*Global Variables*/

#ifndef ROBOT

static char* xbee_com_port = XBEE_PORT_DEFAULT;

static int xbee_stream;

static pthread_t* xbee_listen_thread;

#endif

// TODO: clarify buffers, what they're used for, etc

// a buffer for data received from the XBee

char arrival_buf[XBEE_BUFFER_SIZE];

// location of last unread byte in buffer

volatile int buffer_last = 0;

// first unread byte in buffer

volatile int buffer_first = 0;

//used to store packets as they are read

static char xbee_buf[PACKET_BUFFER_SIZE];

static int currentBufPos = 0;

//XBee status

static unsigned int xbee_panID = XBEE_PAN_DEFAULT;

static unsigned int xbee_pending_panID = XBEE_PAN_DEFAULT;

static int xbee_channel = XBEE_CHANNEL_DEFAULT;

static int xbee_pending_channel = XBEE_CHANNEL_DEFAULT;

static volatile unsigned int xbee_address = 0;

/*Function Implementations*/

#ifdef ROBOT

/**

 * Interrupt for the robot. Adds bytes received from the xbee

 * to the buffer.

 **/

#ifndef FIREFLY

ISR(USART1_RX_vect)

{

        char c = UDR1;

        arrival_buf[buffer_last] = c;

        int t = buffer_last + 1;

        if (t == XBEE_BUFFER_SIZE)

                t = 0;

        if (t == buffer_first)

        {

                WL_DEBUG_PRINT("\nOut of space in buffer.\n");

        }

        buffer_last = t;

}

#else

SIGNAL(SIG_USART0_RECV)

{

        char c = UDR0;

        arrival_buf[buffer_last] = c;

        int t = buffer_last + 1;

        if (t == XBEE_BUFFER_SIZE)

                t = 0;

        if (t == buffer_first)

        {

                WL_DEBUG_PRINT("Out of space in buffer.\n");

        }

        buffer_last = t;

}

#endif

#else

// Computer code

/**

 * Thread that listens to the xbee.

 **/

static void* listen_to_xbee(void* x)

{

        char c;

        while (1)

        {

                if (xbee_read(&c, 1) != 0) {

                        WL_DEBUG_PRINT("xbee_read failed.\n");

                        return NULL;

                }

                arrival_buf[buffer_last] = c;

                int t = buffer_last + 1;

                if (t == XBEE_BUFFER_SIZE)

                        t = 0;

                if (t == buffer_first)

                {

                        WL_DEBUG_PRINT("Out of space in buffer.\n");

                }

                buffer_last = t;

                usleep(1000);

        }

        return NULL;

}

#endif

/**

 * Initializes the XBee library so that other functions may be used.

 **/

int xbee_lib_init()

{

  if (xbee_init() != 0) {

    usb_puts("xbee_init error");

    return -1;

  }

        WL_DEBUG_PRINT("in xbee_init\n");

#ifdef ROBOT

        //enable the receiving interrupt

#ifdef FIREFLY

        UCSR0B |= _BV(RXCIE) | _BV(RXEN);

#else

#ifdef BAYBOARD

        UCSR1B |= _BV(RXCIE1);

#else

        UCSR1B |= _BV(RXCIE);

#endif

#endif

        sei();

#else

        xbee_stream = open(xbee_com_port, O_RDWR);

        if (xbee_stream == -1/* || lockf(xbee_stream, F_TEST, 0) != 0*/)

        {

                WL_DEBUG_PRINT("Failed to open connection to XBee on port ");

                WL_DEBUG_PRINT_INT(xbee_com_port);

                WL_DEBUG_PRINT(".\n");

                return -1;

        } else {

          WL_DEBUG_PRINT("Successfully opened connection to XBee on port ");

                WL_DEBUG_PRINT_INT(xbee_com_port);

                WL_DEBUG_PRINT(".\n");

        }

        // set baud rate, etc. correctly

        struct termios options;

        tcgetattr(xbee_stream, &options);

        cfsetispeed(&options, B9600);

        cfsetospeed(&options, B9600);

        options.c_iflag &= ~ICRNL;

        options.c_oflag &= ~OCRNL;

        options.c_cflag |= (CLOCAL | CREAD);

        options.c_cflag &= ~PARENB;

        options.c_cflag &= ~CSTOPB;

        options.c_cflag &= ~CSIZE;

        options.c_cflag |= CS8;

        options.c_lflag &= ~ICANON;

        options.c_cc[VMIN] = 1;

        options.c_cc[VTIME] = 50;

        if (tcsetattr(xbee_stream, TCSANOW, &options))

        {

                WL_DEBUG_PRINT("Error setting attributes.\n");

                return -1;

        }

        xbee_listen_thread = (pthread_t*)malloc(sizeof(pthread_t));

        if (xbee_listen_thread == NULL)

        {

                WL_DEBUG_PRINT("Malloc failed.\n");

                return -1;

        }

        int ret = pthread_create(xbee_listen_thread, NULL, listen_to_xbee, NULL);

        if (ret)

        {

                WL_DEBUG_PRINT("Failed to create listener thread.\n");

                return -1;

        }

#endif

        WL_DEBUG_PRINT("Entering command mode.\r\n");

        if (xbee_enter_command_mode() != 0) {

    usb_puts("error entering command mode\r\n");

                return -1;

        }

        WL_DEBUG_PRINT("Entered command mode.\r\n");

  // reset baud rate

  WL_DEBUG_PRINT("Resetting Baud to ");

  WL_DEBUG_PRINT(XBEE_BAUD_STR);

  WL_DEBUG_PRINT("\r\n");

  // set baud on xbee

//#if (XBEE_BAUD == 250000)

#if (XBEE_BAUD == 115200)

  xbee_send_string("ATBD7\r\n");

#elif (XBEE_BAUD == 57600)

  xbee_send_string("ATBD6\r\n");

#elif (XBEE_BAUD == 38400)

  xbee_send_string("ATBD5\r\n");

#elif (XBEE_BAUD == 19200)

  xbee_send_string("ATBD4\r\n");

#elif (XBEE_BAUD == 9600)

  // already at this baud rate

  //xbee_send_string("ATBD3\r\n");

#else

  WL_DEBUG_PRINT("undefined baud rate\r\n");

#endif  

  // exit command mode

  xbee_wait_for_ok();

  WL_DEBUG_PRINT("got ok from baud reset\r\n");

  xbee_send_string("ATCN\r\n");

  xbee_wait_for_ok();

  WL_DEBUG_PRINT("got ok from exiting command mode\r\n");

  // set UART baud

#if (XBEE_BAUD == 250000)

  UBRR1H = 0x00;

  UBRR1L = 3;

  UCSR1A |= _BV(U2X1);

#elif (XBEE_BAUD == 115200)

  UBRR1H = 0x00;

  UBRR1L = 8;

  UCSR1A |= _BV(U2X1);

#elif (XBEE_BAUD == 57600)

  UBRR1H = 0x00;

  UBRR1L = 16;

  UCSR1A |= _BV(U2X1);

#elif (XBEE_BAUD == 38400)

  UBRR1H = 0x00;

  UBRR1L = 25;

  UCSR1A |= _BV(U2X1);

#elif (XBEE_BAUD == 19200)

  UBRR1H = 0x00;

  UBRR1L = 51;

  UCSR1A |= _BV(U2X1);

#elif (XBEE_BAUD == 9600)

  /* this is the default baud rate, so do nothing

  UBRR1H = 0x00;

  UBRR1L = 103;

  UCSR1A |= _BV(U2X1);*/

#else //Baud rate is defined in the header file, we should not get here

  return 0;

#endif

  delay_ms(50);

  // enter command mode

  WL_DEBUG_PRINT("entering command mode 2\r\n");

  xbee_send_string("+++");

  xbee_wait_for_ok();

  WL_DEBUG_PRINT("entered command mode 2\r\n");

  if (xbee_enter_api_mode() != 0) {

    WL_DEBUG_PRINT("can't enter api mode\r\n");

                return -1;

        }

        WL_DEBUG_PRINT("Entered api mode.\r\n");

        if (xbee_exit_command_mode() != 0) {

    WL_DEBUG_PRINT("can't exit command mode\r\n");

          return -1;

        }

        WL_DEBUG_PRINT("Left command mode.\r\n");

  // get MY address

        if (xbee_send_read_at_command("BD")) {

    WL_DEBUG_PRINT("can't send BD command\r\n");

                return -1;

        }

        WL_DEBUG_PRINT("Getting ATBD rate.\n");

  // get MY address

        if (xbee_send_read_at_command("MY")) {

    WL_DEBUG_PRINT("can't send my command\r\n");

                return -1;

        }

        WL_DEBUG_PRINT("Getting ATMY address.\n");

#ifndef ROBOT

        int i;

        for (i = 0; xbee_address == 0 && i < XBEE_GET_PACKET_TIMEOUT; i++) {

          ret = xbee_get_packet(NULL);

          usleep(1000);

/*           if (ret == -1) { */

/*             WL_DEBUG_PRINT("xbee_get_packet(NULL) failed.\n"); */

/*             return -1; */

/*           } */

        }

#else

        //wait to return until the address is set

  //TODO: this shouldn't wait indefinitely.  There should be some sort of reasonable timeout

  // so if the address is never set right, an error can be returned instead of having the

  // robot hang forever

        while (xbee_address == 0) {

          xbee_get_packet(NULL);

        }

#endif

        WL_DEBUG_PRINT("Got ATMY address.\n");

#ifndef ROBOT

        if (i == XBEE_GET_PACKET_TIMEOUT) { // We timed-out.

          WL_DEBUG_PRINT("xbee_get_packet timed out.\n");

          return -1;

        } else {

          return 0;

        }

#else

        return 0;

#endif

}

/**

 * Call when finished using the XBee library. This releases

 * all sued resources.

 **/

void xbee_terminate()

{

        #ifndef ROBOT

        pthread_cancel(*xbee_listen_thread);

    pthread_join(*xbee_listen_thread, NULL);

        free(xbee_listen_thread);

        lockf(xbee_stream, F_ULOCK, 0);

        close(xbee_stream);

  #else

  xbee_exit_api_mode();

        #endif

}

/**

 * Send a buffer buf of size bytes to the XBee.

 *

 * @param buf the buffer of data to send

 * @param size the number of bytes to send

 **/

static int xbee_send(char* buf, int size)

{

#ifdef ROBOT

        int i;

        for (i = 0; i < size; i++) {

                xbee_putc(buf[i]);

        }

        return 0;

#else

        int ret = write(xbee_stream, buf, size);

        //success

        if (ret == size)

                return 0;

        if (ret == -1)

        {

                //interrupted by system signal, probably timer interrupt.

                //just try again

                if (errno == 4)

                {

                        return xbee_send(buf, size);

                }

                WL_DEBUG_PRINT("Failed to write to xbee\r\n");

                return -1;

        }

        //write was interrupted after writing ret bytes

        return xbee_send(buf + ret, size - ret);

#endif

}

/**

 * Sends a string to the XBee.

 *

 * @param c the string to send to the XBEE

 **/

static int xbee_send_string(char* c)

{

        return xbee_send(c, strlen(c));

}

#ifndef ROBOT

static int xbee_read(char* buf, int size)

{

        if (read(xbee_stream, buf, size) == -1) {

                WL_DEBUG_PRINT("Failed to read from xbee.\r\n");

                return -1;

        }

        return 0;

}

#endif

/**

 * Enter into command mode.

 **/

static int xbee_enter_command_mode()

{

        if (xbee_send_string("+++") != 0) {

                return -1;

        }

        if (xbee_wait_for_ok() != 0) {

          return -1;

        }

          return 0;

}

/**

 * Exit from command mode.

 **/

static int xbee_exit_command_mode()

{

        if (xbee_send_string("ATCN\r") != 0) {

                return -1;

        }

        xbee_wait_for_ok();

        return 0;

}

/**

 * Enter API mode.

 **/

static int xbee_enter_api_mode()

{

        if (xbee_send_string("ATAP 1\r") != 0) {

                return -1;

        }

        xbee_wait_for_ok();

        return 0;

}

/**

 * Exit API mode.

 **/

static int xbee_exit_api_mode()

{

        if (xbee_send_modify_at_command("AP","0") != 0) {

                return -1;

        }

        return 0;

}

/**

 * Wait until the string "OK\r" is received from the XBee.

 **/

static int xbee_wait_for_ok()

{

        return xbee_wait_for_string("OK\r", 3);

}

/**

 * Delay until the specified string is received from

 * the XBee. Discards all other XBee data.

 *

 * ********* Robot often hangs here ****************

 *

 * @param s the string to receive

 * @param len the length of the string

 **/

static int xbee_wait_for_string(char* s, int len)

{

        char* curr = s;

  unsigned int i=0;

        while (curr - s < len) {

    WL_DEBUG_PRINT("waiting for string\r\n");

                // check if buffer is empty

                if (buffer_last != buffer_first) {

                        char c = arrival_buf[buffer_first++];

                        if (buffer_first == XBEE_BUFFER_SIZE) {

                                buffer_first = 0;

                        }

      WL_DEBUG_PRINT("buffer char|");

      WL_DEBUG_PRINT_CHAR(c);

      WL_DEBUG_PRINT("|\r\n");

                        if (c == *curr) {

                                curr++;

                        } else {

#ifndef ROBOT

                          //return -1; // Computer is less forgiving.

                          curr = s;

#else

                          curr = s;

#endif

                        }

                } // else buffer is empty.

#ifndef ROBOT

                usleep(100);

#endif

        }

  if (i >= 10000)

    return -1;

        return 0;

}

/**

 * Verifies that the packets checksum is correct.

 * (If the checksum is correct, the sum of the bytes

 * is 0xFF.)

 *

 * @param packet the packet received. This includes the first

 * three bytes, which are header information from the XBee.

 *

 * @param len The length of the packet received from the XBee

 *

 * @return 0 if the checksum is incorrect, nonzero

 * otherwise

 **/

int xbee_verify_checksum(char* packet, int len)

{

        unsigned char sum = 0;

        int i;

        for (i = 3; i < len; i++)

                sum += (unsigned char)packet[i];

        return sum == 0xFF;

}

/**

 * Returns the checksum of the given packet.

 *

 * @param buf the data for the packet to send

 * @param len the length of the packet in bytes

 *

 * @return the checksum of the packet, which will

 * become the last byte sent in the packet

 **/

char xbee_compute_checksum(char* buf, int len)

{

        int i;

        unsigned char sum = 0;

        for (i = 0; i < len; i++)

                sum += (unsigned char)buf[i];

        return 0xFF - sum;

}

/**

 * Adds header information and checksum to the given

 * packet and sends it. Header information includes

 * XBEE_FRAME_START and the packet length, as two bytes.

 *

 * @param buf the packet data

 * @param len the size in bytes of the packet data

 *

 **/

static int xbee_send_frame(char* buf, int len)

{

        char prefix[3];

        prefix[0] = XBEE_FRAME_START;

        prefix[1] = (len & 0xFF00) >> 8;

        prefix[2] = len & 0xFF;

        char checksum = xbee_compute_checksum(buf, len);

        if (xbee_send(prefix, 3) != 0) {

                return -1;

        }

        if (xbee_send(buf, len) != 0) {

                return -1;

        }

        if (xbee_send(&checksum, 1) != 0) {

                return -1;

        }

        return 0;

}

/**

 * Sends an AT command to read a parameter.

 *

 * @param command the AT command to send. For exmaple,

 * use ID to read the PAN ID and MY to return the XBee ID.

 * See the XBee reference guide for a complete listing.

 **/

int xbee_send_read_at_command(char* command)

{

        return xbee_send_modify_at_command(command, NULL);

}

/**

 * Sends the given AT command.

 *

 * @param command the AT command to send (e.g., MY, ID)

 * @param value the value to pass as a parameter

 * (or NULL if there is no parameter)

 **/

static int xbee_send_modify_at_command(char* command, char* value)

{

        char buf[16];

        int i;

        buf[0] = XBEE_FRAME_AT_COMMAND;

        buf[1] = 1;

        buf[2] = command[0];

        buf[3] = command[1];

        int valueLen = 0;

        if (value != NULL)

        {

                valueLen = strlen(value);

                if (valueLen > 8)

                {

                        WL_DEBUG_PRINT("AT Command too large.\r\n");

                        return -1;

                }

                for (i = 0; i < valueLen; i++) {

                        buf[4 + i] = value[i];

                }

        }

        return xbee_send_frame(buf, 4 + valueLen);

}

/**

 * Send the specified packet.

 *

 * @param packet the packet data to send

 * @param len the number of bytes in the packet

 *

 * @param dest the ID of the XBee to send the packet to,

 * or XBEE_BROADCAST to send the message to all robots

 * in the PAN.

 *

 * @param options a combination of the flags

 * XBEE_OPTIONS_NONE, XBEE_OPTIONS_DISABLE_RESPONSE and

 * XBEE_OPTIONS_BROADCAST_ALL_PANS

 *

 * @param frame the frame number to associate this packet

 * with. This will be used to identify the response when

 * the XBee alerts us as to whether or not our message

 * was received.

 **/

int xbee_send_packet(char* packet, int len, int dest, char options, char frame)

{

        char buf[5];

        char prefix[3];

        int i;

        unsigned char checksum = 0;

        if (len > 100)

        {

                WL_DEBUG_PRINT("Packet is too large.\r\n");

                return -1;

        }

        //data for sending request

        buf[0] = XBEE_FRAME_TX_REQUEST_16;

        buf[1] = frame;

        buf[2] = (dest >> 8) & 0xFF;

        buf[3] = dest & 0xFF;

        buf[4] = options;

        //packet prefix, do this here so we don't need an extra buffer

        prefix[0] = XBEE_FRAME_START;

        prefix[1] = ((5 + len) & 0xFF00) >> 8;

        prefix[2] = (5 + len) & 0xFF;

        for (i = 0; i < 5; i++)

                checksum += (unsigned char)buf[i];

        for (i = 0; i < len; i++)

                checksum += (unsigned char)packet[i];

        checksum = 0xFF - checksum;

        if (xbee_send(prefix, 3) != 0) {

                return -1;

        }

        if (xbee_send(buf, 5) != 0) {

                return -1;

        }

        if (xbee_send(packet, len) != 0) {

                return -1;

        }

        if (xbee_send((char*)&checksum, 1) != 0) {

                return -1;

        }

        return 0;

}

/**

 * Reads a packet received from the XBee. This function

 * is non-blocking. The resulting packet is stored in dest.

 * Only returns transmission response packets and

 * received packets. The returned packet does not include

 * header information or the checksum. This method also

 * handles special packets dealt with by the XBee library,

 * and so should be called frequently while the XBee is in

 * use.<br><br>

 *

 * The first byte of the packet will be either

 * XBEE_TX_STATUS or XBEE_RX to indicated

 * a response to a sent message or a received message,

 * respectively.<br><br>

 *

 * For a status response packet:<br>

 * The first byte will be XBEE_TX_STATUS.<br>

 * The second byte will be the frame number.<br>

 * The third byte will be the result. 0 indicates success,

 * and nonzero indicates that an error ocurred in

 * transmitting the packet.<br><br>

 *

 * For a received packet:<br>

 * The first byte will be XBEE_RX.<br>

 * The second and third bytes will be the 16-bit

 * address of the packet's sender.<br>

 * The fourth byte is the signal strength.<br>

 * The fifth byte is 1 if the packet were sent to

 * a specific address, and 2 if it is a broadcast packet.<br><br>

 *

 * @param dest set to the packet data

 * @return the length of the packet, or -1 if no packet

 * is available

 **/

int xbee_get_packet(unsigned char* dest)

{

     int ret;

        //start reading a packet with XBEE_FRAME_START

        if (currentBufPos == 0)

        {

                do

                {

                        if (buffer_first == XBEE_BUFFER_SIZE)

                                buffer_first = 0;

                        // check if buffer is empty

                        if (buffer_first == buffer_last) {

        WL_DEBUG_PRINT("buffer empty\r\n");

                                return -1;

                        }

                } while (arrival_buf[buffer_first++] != XBEE_FRAME_START);

                if (buffer_first == XBEE_BUFFER_SIZE) {

                        buffer_first = 0;

                }

                xbee_buf[0] = XBEE_FRAME_START;

                currentBufPos++;

        }

        int len = -1;

        if (currentBufPos >= 3) {

                len = (int)xbee_buf[2] + ((int)xbee_buf[1] << 8);

        }

        while (len == -1 //packet length has not been read yet

                || currentBufPos < len + 4)

        {

                if (currentBufPos == 3)

                {

                        len = (int)xbee_buf[2] + ((int)xbee_buf[1] << 8);

                        if (len > 120)

                        {

                                WL_DEBUG_PRINT("Packet too large. Probably error in XBee transmission.\r\n");

                                currentBufPos = 0;

                                return -1;

                        }

                }

                // check if buffer is empty

                if (buffer_first == buffer_last) {

      WL_DEBUG_PRINT("Buffer empty 2\r\n");

                        return -1;

                }

                xbee_buf[currentBufPos++] = arrival_buf[buffer_first++];

                if (buffer_first == XBEE_BUFFER_SIZE) {

                        buffer_first = 0;

                }

        }

        currentBufPos = 0;

        if (!xbee_verify_checksum(xbee_buf, len + 4))

        {

                WL_DEBUG_PRINT("XBee checksum failed.\r\n");

                return -1;

        }

        //we will take care of the packet

        ret = xbee_handle_packet(xbee_buf+3, len);

        if (ret == 1) {

                return 3;

        } else if (ret == -1) {

    WL_DEBUG_PRINT("xbee_handle_packet returned -1\r\n");

    return -2;

  }

        if (dest == NULL) {

    WL_DEBUG_PRINT("dest buffer is null\r\n");

                return -1;

        }

        int i;

        for (i = 3; i < len + 3; i++) {

                dest[i - 3] = xbee_buf[i];

        }

        return len;

}

/**

 * Handles modem status packets.

 *

 * @param status the type of status packet received.

 **/

void xbee_handle_status(char status)

{

        switch (status)

        {

                case 0:

                        WL_DEBUG_PRINT("XBee hardware reset.\r\n");

                        break;

                case 1:

                        WL_DEBUG_PRINT("Watchdog timer reset.\r\n");

                        break;

                case 2:

                        WL_DEBUG_PRINT("Associated.\r\n");

                        break;

                case 3:

                        WL_DEBUG_PRINT("Disassociated.\r\n");

                        break;

                case 4:

                        WL_DEBUG_PRINT("Synchronization lost.\r\n");

                        break;

                case 5:

                        WL_DEBUG_PRINT("Coordinator realignment.\r\n");

                        break;

                case 6:

                        WL_DEBUG_PRINT("Coordinator started.\r\n");

                        break;

        }

}

/**

 * Handles AT command response packets.

 * @param command the two character AT command, e.g. MY or ID

 * @param result 0 for success, 1 for an error

 * @param extra the hex value of the requested register

 * @param extraLen the length in bytes of extra

 **/

static int xbee_handle_at_command_response(char* command, char result, char* extra, int extraLen)

{

        if (result == 1)

        {

                WL_DEBUG_PRINT("Error with AT");

                WL_DEBUG_PRINT(command);

                WL_DEBUG_PRINT(" packet. Result = ");

    switch(result) {

    case 1:

      WL_DEBUG_PRINT("ERROR\r\n");

      break;

    case 2:

      WL_DEBUG_PRINT("Invalid Command\r\n");

      break;

    case 3:

      WL_DEBUG_PRINT("Invalid Parameter\r\n");

      break;

    }

    return -1;

        }

        WL_DEBUG_PRINT("AT");

        WL_DEBUG_PRINT(command);

        WL_DEBUG_PRINT(" command was successful.\r\n");

        if (command[0] == 'I' && command[1] == 'D')

        {

                xbee_panID = xbee_pending_panID;

                WL_DEBUG_PRINT("PAN ID set to ");

                WL_DEBUG_PRINT_INT(xbee_panID);

                WL_DEBUG_PRINT(".\r\n");

                return 0;

        }

        if (command[0] == 'C' && command[1] == 'H')

        {

                xbee_channel = xbee_pending_channel;

                WL_DEBUG_PRINT("Channel set to ");

                WL_DEBUG_PRINT_INT(xbee_channel);

                WL_DEBUG_PRINT(".\r\n");

                return 0;

        }

  if (command[0] == 'N' && command[1] == 'D')

        {

                WL_DEBUG_PRINT("ND - extra=");

    WL_DEBUG_PRINT(extra);

                WL_DEBUG_PRINT("\r\n");

                return 0;

        }

   if (command[0] == 'B' && command[1] == 'D')

        {

                WL_DEBUG_PRINT("BD - extra=");

    WL_DEBUG_PRINT(extra);

                WL_DEBUG_PRINT("\r\n");

                return 0;

        }

        if (command[0] == 'M' && command[1] == 'Y' && extraLen != 0)

        {

                xbee_address = 0;

                int i;

                for (i = 0; i < extraLen; i++) {

                        xbee_address = (xbee_address << 8) + extra[i];

                }

                WL_DEBUG_PRINT("XBee address is ");

                WL_DEBUG_PRINT_INT(xbee_address);

                WL_DEBUG_PRINT(".\r\n");

                if (xbee_address == 0)

                {

                        WL_DEBUG_PRINT("XBee 16-bit address must be set using ATMY.\r\n");

                        #ifndef ROBOT

                        exit(0);

                        #endif

                }

        }

  return 0;

}

/**

 * Attempts to handle the packet if it is dealt with

 * by the library.

 * We will handle the following packet types:

 *    Modem Status

 *    AT Command Response

 *

 * @param packet the packet to handle

 * @param len the length of the packet

 *

 * @return 1 if we have handled the packet, 0 otherwise

 */

static int xbee_handle_packet(char* packet, int len)

{

        char command[3] = {1, 2, 3};

        if (len <= 0) //this should not happend

        {

                WL_DEBUG_PRINT("Non-positive packet length.\r\n");

                return 0;

        }

        switch ((unsigned char)packet[0]) //packet type

        {

                case XBEE_FRAME_STATUS:

                        xbee_handle_status(packet[1]);

                        return 1;

                case XBEE_FRAME_AT_COMMAND_RESPONSE:

                        command[0] = packet[2];

                        command[1] = packet[3];

                        command[2] = 0;

                        if (xbee_handle_at_command_response(command, packet[4], packet + 5, len - 5) != 0)

        return -1;

      else

        return 1;

        }

        return 0;

}

/**

 * Sets the personal area network id.

 *

 * @param id the new personal area network (PAN) id

 **/

int xbee_set_pan_id(int id)

{

        char s[3];

        s[0] = (id >> 8) & 0xFF;

        s[1] = id & 0xFF;

        s[2] = 0;

        xbee_pending_panID = id;

        return xbee_send_modify_at_command("ID", s);

}

/**

 * Get the PAN ID for the XBee.

 *

 * @return the personal area network id, or

 * XBEE_PAN_DEFAULT if it has not yet been set.

 **/

unsigned int xbee_get_pan_id()

{

        return xbee_panID;

}

/**

 * Set the channel the XBee is using.

 *

 * @param channel the channel the XBee will not use,

 * between 0x0B and 0x1A

 *

 * @see xbee_get_channel

 **/

int xbee_set_channel(int channel)

{

        if (channel < 0x0B || channel > 0x1A)

        {

                WL_DEBUG_PRINT("Channel out of range.\r\n");

                return -1;

        }

        char s[3];

        s[0] = channel & 0xFF;

        s[1] = 0;

        xbee_pending_channel = channel;

        return xbee_send_modify_at_command("CH", s);

}

/**

 * Returns the channel which the XBee is currently using.

 *

 * @return the channel the XBee is using

 *

 * @see xbee_set_channel

 **/

int xbee_get_channel(void)

{

        return xbee_channel;

}

/**

 * Get the 16-bit address of the XBee.

 * This is used to specify who to send messages to

 * and who messages are from.

 *

 * @return the 16-bit address of the XBee.

 **/

unsigned int xbee_get_address()

{

        return xbee_address;

}

#ifndef ROBOT

void xbee_set_com_port(char* port)

{

        xbee_com_port = port;

}

#endif

/**@} **/ // end xbee group