COLONYCOLONYWIRELESSWIRELESS

September 26, 2008September 26, 2008

Outline

1.Motivation and Goals

2.Introduction to the XBee

3.The Wireless Library

4.Example Packet Group

5.The Token Ring

6.Questions

Why Wireless?

Enables Cooperation Allows Sharing of Sensor Information

– BOM readings for cooperative searching Synchronizes BOM flashes

– Prevents interference from multiple robots Controls access to resources, such as

charging stations External monitoring through ColoNet

XBee module

ZigBee wireless protocol– Open industry standard– IEEE 802.15.4– Low-cost, low-power– 2.4GHZ– Widely used in sensor networks

XBee wireless module– www.maxstream.net– 30m indoor range / 100m outdoor range– Simple interface

5

Selected XBee Features

16-bit Addressing Personal Area Networks (PANs)

– May send packets only to your PAN– Able to change PAN at any time

16 Channels– XBees in different channels cannot communicate

API Mode– Provides more features

Interference prevention

6

XBee Packets

Send up to 100 bytes as a packet Send to a single robot, a PAN, or everyone Optionally set a frame number

– Confirms reception of packets to single robots

7

Packet Types

Robot to Robot– Send to a single XBee– Specified by 16-bit address– ACK confirms reception, matched with frame

PAN– Send to all XBees in our current PAN

Global– Send to all XBees in our channel

8

Wireless Library

Simple Modular Functional

#include <dragonfly_lib.h>#include <wireless.h>

int main(){ dragonfly_init(ALL_ON); wl_init();

while (1) { wl_do(); do_stuff(); } return 0;}

9

Packet Groups

Organize packets into groups with similar functions for modularity

Examples:– Error Messages– Token Ring

Each packet in a group shares a group code Individual packets have packet types Group and type uniquely identify a packet Packets can be of any length (< 100 bytes)

10

Packet Group Handlers

Registered with the wireless library to receive packets from a specific group

Contains– Group Code– Function to handle received packets– Function to handle ACKs or failures– Function to call on timer tick– Function to call when the packet group is

removed

11

C Programming: Function Pointers

Variables which point to the address of a function

When called, call thefunction they point to

void foo(void) { printf(“Hello World!”);}

void bar(void) { printf(“Goodbye World!”);

void (*func)(void) = &foo;

func();>> Hello World!func = &bar;func();>> Goodbye World!

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Packet Group Handlers (contd.)

typedef struct{ unsigned int groupCode;

void (*timeout_handler) (void); void (*handle_response) (int frame, int received); void (*handle_receive) (char type, int source, unsigned char* packet, int length); void (*unregister) (void);} PacketGroupHandler;

Register packet groups with wl_packet_group_register

13

Packet Group Handler Example

Creating a packet group to control robots through ColoNet

Only need to respond to commands, so will only implement handle_receive

14

ColoNet Example (contd.)

void colonet_receive (char type, int source, unsigned char* packet, int length){ switch (type) { case BEEP: buzzer_chirp(1000, 200); break; case HUNT_RON: find_ron(); ram_ron(); break; case SELF_DESTRUCT: self_destruct(); break; }}

15

ColoNet Example (contd.)

PacketGroupHandler colonetHandler = {COLONET_GROUP, NULL, NULL, &colonet_receive, NULL}

int main(){ dragonfly_init(ALL_ON); wl_init(); wl_register_packet_group(&colonetHandler); while (1) wl_do();}

This program will obey all of ColoNet’s commands.

16

Sending Packets

Now we are able to receive packets But how do we send packets? Simply call these functions in wireless.h

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

Send a packet to a specific robot in any PAN. void wl_send_robot_to_robot_packet (char group, char type, char *data, int len, int dest, char frame)Send a packet to a specific robot in our PAN. void wl_send_global_packet (char group, char type, char *data, int len, char frame)Send a packet to all robots. void wl_send_pan_packet (char group, char type, char *data, int len, char frame)Send a packet to all robots in our PAN.

17

Colonet Example

We can receive wireless packets, but we still need to send them

void send_beep(int robot){ wl_send_robot_to_robot_global_packet(COLONET_GROUP, BEEP, NULL, 0, robot, 0)}

void hunt_ron(){ wl_send_global_packet(COLONET_GROUP, HUNT_RON, NULL, 0, 0);}

18

Colonet Example

void bomb_squad(){ wl_send_global_packet(COLONET_GROUP, SELF_DESTRUCT, NULL, 0, 0);}

19

Colonet Example

Now, ColoNet is able to control robots using the ColoNet packet group.

Bearing and Orientation Module (BOM)

IR emitter/detector ring Emitter mode

– All emitters are powered simultaneously (beacon)

Detector mode– Detectors can be polled

for analog intensity readings

Used for localization– Determining relative

directions of robots– Seeking charging station

21

Why do we need a token ring?

If more than one BOM flashes at once, other robots won’t know which is which

Only one BOM can flash at a time Token ring controls which BOM can flash

22

Token Ring

Only robot with “token” may flash BOM Once BOM is flashed, the robot with the

token passes it to the next robot (determined by XBee ID)

Sends BOM readings for the other robots with token, so that each robot has a sensor matrix of all BOM readings

23

Sensor Matrix

Each robot passes its own sensor readings with the token

All robots form a sensor matrix, storing relative location of all robots

Various applications, including– Seeking a charging station– Cooperative Maze Solving– Following another robot

24

Ad-hoc Network

If a robot does not pass the token quickly enough, or dies, the previous robot removes it from the network and it must rejoin

Robots can freely join and leave the network, and the token continues to be passed

To join the token ring, a robot sends a join request

Preceding robot in ring adds the robot, and sends the token to him next time

25

Ad-hoc Network Advantages

Leaderless Network Stable when robots die New robots can join easily

26

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

27

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

28

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

29

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

30

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

31

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

Bot1 has been eliminated by ColoNet!

32

Token Ring Example

Ron

Bot 1

Bot 2

Bot 3

- Token

Bot1 has been eliminated by ColoNet!

Bot1 does not respond, so Ron realizes it is dead. He sends the token to Bot2 instead.

33

Using the Token Ring

#include <dragonfly_lib.h>#include <wireless.h>#include <wl_token_ring.h>

int main(){ dragonfly_init(ALL_ON); wl_init(); wl_token_ring_register(); while (1) wl_do();}

To use the wireless library, set USE_WIRELESS = 1 in the Makefile

34

Summary

Packet Groups to add wireless functionality Token Ring to find relative locations of robots

35

Troubleshooting

Connect to dongle at 9600 Baud '+++' enters command mode Only XBees with the latest firmware support

the wireless library (ATVR) Xbee ID ('ATMY' to read, 'ATMY num' to set) 0 < ID < XBEE_MAX_ID, must be unique Default Channel should be C (ATCH) ATWR to save settings Running the motors may cause interference

36

Wireless Applications

Tag / Lemmings Cooperative Maze Solving Marching Band Task Allocation Wireless monitoring and control with Colonet Autonomous Recharging Mapping

Joke

Even bytes get lonely for a little bit.