Colony

 * Copyright (c) 2007 Colony Project

 *

 *

 *

 * @brief Contains definitions for the wireless library.

 * Contains functions for the wireless library.

 * @author Brian Coltin, Colony Project, CMU Robotics Club

//Note: If this is raised above 16, we will need to do

//something about frame numbers for TX Status packets.

/**

 * The maximum number of packet groups.

 **/

//TODO: a PacketGroupHandler is at least 10 bytes (I don't know if function pointers are 2 bytes

// or 4 bytes).  That means that in the c file, your array of packet groups is at least 160 bytes.

// Normally that might be fine (the robot's avr chips have 4k SRAM), but austin's chip only has

// 1k SRAM, so if this number can be reduced or if the size of the struct could be reduced, that would be a plus.

#define WL_MAX_PACKET_GROUPS 16

 * @brief Wireless definitions.

 * Contains functions and definitions for dealing with wireless functionality.<br><br>

 * The wireless library provides a modular method for dealing with

 * wireless packets, by allowing packet groups to be registered.

 * A packet group is a collection of packets which share a packet

 * group code. Each packet in the group also has a type. A packet

 * group code and type are sent with each packet. When a packet

 * with a group code registered in the wireless library is

 * received, the corresponding event handler is called. The

 * event handler uses the packet type and other information

 * stored in the packet to respond.<br><br>

 *

 * This architecture allows different wireless functionality to be

 * defined and handled separately, making it simpler and more

 * efficient to take advantage of the XBee's wireless functionality.

 *

 * handlers for various events which can occur related to a packet

 * group.

//TODO: the order of member variables in this struct should be changed in case the compile packs the struct

// In order to achieve the best packing, the variables should be listed in order of decreasing memory size.

// Thus, pointers should be first, followed by int, followed by char.

typedef struct

{

	/**

	 * The group code for this packet group. This number

	 * must be unique. The maximum number of packet groups

	 * is defined by WL_MAX_PACKET_GROUPS.

	 **/

  //TODO: if this number must be less than or equal to WL_MAX_PACKET_GROUPS, don't you only need

  // one byte for it and it can be made an unsigned char?

	unsigned int groupCode;

	/**

	 * Called every half second (not in interrupt,

	 * but in wl_do).

	 **/

	void (*timeout_handler) (void);

	/**

	 * Called when a transmit status packet is received

	 * from the XBee where the first four bits of the frame

	 * are  the group code.

	 *

	 * @param frame the last four bits of the frame

	 * @param received is true if we received an ack, 0 if

	 * we did not.

	 **/

	void (*handle_response) (int frame, int received);

	/**

	 * Called when we receive a packet from this group.

	 *

	 * @param type the packet type

	 * @param source the 16-bit address of the XBee this

	 * packet was sent from

	 * @param packet the packet received

	 * @param length the length of the packet

	 **/

	void (*handle_receive) (char type, int source, unsigned char* packet, int length);

	/**

	 * Called for any cleanup when the network is turned off.

	 **/

	void (*unregister) (void);

} PacketGroupHandler;

/**@brief Initialize the wireless library **/

int wl_init(void);

/**@brief Uninitialize the wireless library **/

void wl_terminate(void);

/**@brief Perform wireless library functionality **/

void wl_do(void);

/**@brief Register a packet group with the wireless library **/

void wl_register_packet_group(PacketGroupHandler* h);

/**@brief Unregister a packet group with the wireless library **/

void wl_unregister_packet_group(PacketGroupHandler* h);

/**@brief Send a packet to a specific robot in any PAN **/

int wl_send_robot_to_robot_global_packet(char group, char type, char* data, int len, int dest, char frame);

/**@brief Send a packet to a specific robot in our PAN **/

int wl_send_robot_to_robot_packet(char group, char type, char* data, int len, int dest, char frame);

/**@brief Send a packet to all robots **/

int wl_send_global_packet(char group, char type, char* data, int len, char frame);

/**@brief Send a packet to all robots in our PAN **/

void wl_send_pan_packet(char group, char type, char* data, int len, char frame);

/**@brief Set the PAN we are using **/

int wl_set_pan(int pan);

/**@brief Get the PAN we are using **/

int wl_get_pan(void);

/**@brief Set the channel we are using **/

int wl_set_channel(int channel);

/**@brief Get the channel we are using **/

int wl_get_channel(void);

/**@brief Get the 16-bit address of the XBee module **/

int wl_get_xbee_id(void);

/**@brief Set the com port on a computer, undefined on the robot.**/

void wl_set_com_port(char* port);

/** @} **/ // end defgroup

 * Copyright (c) 2007 Colony Project

 * Contains definitions for wireless packet groups, packet types,

 * debugging information, etc.

 * @author Brian Coltin, Colony Project, CMU Robotics Club

//return value definitions

#define WL_ERROR_INIT_FAILED 1

#define WL_ERROR_INIT_ALREADY_INITD 2

#define WL_ERROR_LIBRARY_NOT_INITD 3

// Packet Groups and Types

// Error group

#define WL_ERROR_GROUP 1

#define WL_ERROR_STRING_TYPE 1

// Token Ring group

#define WL_TOKEN_RING_GROUP 2

#define WL_TOKEN_PASS 1

#define WL_TOKEN_SENSOR_MATRIX 2

#define WL_TOKEN_BOM_ON 3

#define WL_TOKEN_JOIN 4

#define WL_TOKEN_JOIN_ACCEPT 5

// timing constants

#ifndef FIREFLY

#define BOM_DELAY 100

#else

#define BOM_DELAY 200

#endif

#define DEATH_DELAY 4

#define JOIN_DELAY 8

#endif

#ifdef ROBOT

#endif

#ifdef ROBOT

#define WL_DEBUG_PRINT_INT( i ) usb_puti(i)

#else

 * Copyright (c) 2007 Colony Project

 * @author Brian Coltin, Colony Project, CMU Robotics Club

/**

 * The port to use the XBee from on the computer.

 * Also, a backup port if the other is used.

 **/

#ifndef ROBOT

#define XBEE_PORT_DEFAULT "/dev/ttyUSB1"

/*Definitions*/

int xbee_lib_init(void);

void xbee_terminate(void);

/**@brief Get a packet from the XBee **/

int xbee_get_packet(unsigned char* packet);

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

int xbee_set_pan_id(int id);

unsigned int xbee_get_pan_id(void);

int xbee_set_channel(int channel);

int xbee_get_channel(void);

unsigned int xbee_get_address(void);

/**@brief Set the com port on a computer, undefined on the robot**/

void xbee_set_com_port(char* port);

int xbee_reset(void);

/**@}**/ //end defgroup

#include <dragonfly_lib.h>

#include <wireless.h>

#include <wl_token_ring.h>

/**

 * Tests the token ring and BOM

 * - prints table of bom values for every robot in token ring

 * - takes several seconds to initialize token ring

 */

#define MAX_ROBOTS 16

// set a list of integers to 0

void clearRobots(int* list) {

  for(int i=0;i<MAX_ROBOTS;i++)

    list[i] = 0;

}

int testtokenring(void) {

  usb_init();

	usb_puts("usb turned on\r\n");

  wl_init();

  usb_puts("wireless turned on\r\n");

  wl_token_ring_register();

  wl_token_ring_join(); // join token ring

  usb_puts("token ring joined\r\n");

  int robotList[sizeof(int)*MAX_ROBOTS];

  int numRobots = 0;

  delay_ms(1000);

  // start testing wireless/token ring/BOM

  int i=0;

  while(1) {

    wl_do();

    // only print table every 200 loops

    if (i%200==0) {

      // get token ring size values

      usb_puts("\r\nnumber of robots in token ring:");

      usb_puti(wl_token_get_robots_in_ring());

      usb_puts("\r\nnumber of robots in matrix:"); 

      usb_puti(wl_token_get_num_robots());

      // get list of robots

      numRobots = 0;

      clearRobots(robotList);

      wl_token_iterator_begin();

      while(wl_token_iterator_has_next()) {

        int tmp = wl_token_iterator_next();

        if (tmp < 0)

          break;

        robotList[tmp] = 1;

        numRobots++;

      }

      if (numRobots < 1) {

        usb_puts("\r\nNo BOM table available.");

        continue; // skip table printing

      } else {

        usb_puts("\r\nBOM table: (* indicates this robot)");

      }

      // print table of bom readings between robots

      usb_puts("\r\ns \\ d");

      // print header

      for(int j=0;j<MAX_ROBOTS;j++)

        if (robotList[j]) {

          usb_puts("\t|");

          if (j == wl_get_xbee_id())

            usb_puts("*"); // indicate that this is the current bot

          usb_puti(j);

        }

      usb_puts("\r\n");

      // print body

      for(int l=0;l<MAX_ROBOTS;l++) 

        if (robotList[l]) {        

          if (l == wl_get_xbee_id())

            usb_puts("*"); // indicate that this is the current bot

          usb_puti(l); // print label col

          for(int k=0;k<MAX_ROBOTS;k++) 

            if (robotList[k]) {

              usb_puts("\t|");

              if (k != l) {

                int bom = wl_token_get_sensor_reading(l,k);

                if (bom >= 0 && bom <= 15)

                  usb_puti(bom); // print bom value

              }

            }

          usb_puts("\r\n");

        }

      usb_puts("\r\n");

    }

  }

  // end testing token ring and bom

	return 0;

}

/**

 * Copyright (c) 2007 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 Brian Coltin, Colony Project, CMU Robotics Club

 **/

#include <xbee.h>

#include <wl_defs.h>

#define ROBOT

#define WL_DEBUG

#define WL_DEBUG_PRINT( s ) usb_puts( s )

#define WL_DEBUG_PRINT_INT( i ) usb_puti(i)

#ifndef ROBOT

#include <fcntl.h>

#include <unistd.h>

#include <pthread.h>

#include <errno.h>

#include <termios.h>

#else

#include <serial.h>

#include <avr/interrupt.h>

#endif

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#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

/*Internal Function Prototypes*/

/*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 void 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: is this a good size?

#define XBEE_BUFFER_SIZE	128

#define PACKET_BUFFER_SIZE	108

// 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()

{

	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.\n");

	if (xbee_enter_command_mode() != 0) {

		return -1;

	}

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

	if (xbee_enter_api_mode() != 0) {

		return -1;

	}

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

	if (xbee_exit_command_mode() != 0) {

	     return -1;

	}

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

	if (xbee_send_read_at_command("MY")) {

		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;

	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;

			}

			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

	}

	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) {

				return -1;

			}