Circular counting
Mon, 10/06/2008 - 14:51 — Sofian
This is an important proof-of-concept I wanted to implement with respect to circular serial communication. For nodes in the circular network to be able to send messages to other nodes, they need to be able to send and receive addressed packets. Those packets are relayed through the network until they reach their final destination.
The first kind of packet that I wished to implement is very simple: it allows the node to be aware of the number of nodes in the network. Here is the general algorithm that is run:
generate a unique key
send a packet containing:
this unique key and
a counter with value zero (0)
when receiving a packet:
add one (1) to the counter
compare its key with my unique key
if it's the same key then:
the number of nodes is equal to the counter
else then:
just send the packet to the next node
We can explain it easily with an analogy. Suppose I am in a circular network and I want to know how many nodes there are in that network.
choose a unique color
send an empty basket colored with my unique color
when receiving a basket:
add a rock in it
compare the basket's color with my unique color
if it's the same color then:
the number of nodes is equal to the number of rocks
else then:
just send the basket to the next node
The source code
i2c Loop
I whipped this up very quickly, if there's only ever 2 devices on the BUS then is should prevent collisions. I don't have 2 or 3 arduino's wired up to try it at the moment.
// Wire Receiver / Sender #include int myNodeRef = 1; int nextNode = myNodeRef+1; void setup() { Wire.begin(myNodeRef); // join i2c bus with address #1 Wire.onReceive(receiveEvent); // register event Serial.begin(9600); // start serial for output } void loop() { delay(100); targetNode=5; // want to send a message to device #5 sendaMsg(); // this is used if I'm sending a message } // RECEIVE void receiveEvent(int howMany) { while(1 < Wire.available()) { // loop through all but the last int targetNode = Wire.receive(); // get node number message is intended for char c = Wire.receive(); // receive byte as a character if (targetNode == myNodeRef) { Serial.print(c); // message is for me, print the character } else { passOnMessage; // else, pass the message on to the next node } } } // SEND void sendaMsg() { Wire.beginTransmission(nextNode); // transmit to device next door (#2) Wire.send(targetNode) // tell #2 message is for targetNode (#5) Wire.send("A"); // send one byte Wire.endTransmission(); // stop transmitting delay(50); } // PASS THE MESSAGE ON void passOnMessage() { Wire.beginTransmission(nextNode); // transmit to the node next door (device #2) Wire.send(targetNode) // tell #2 message is for someone elses node (#5) Wire.send(c); // pass on the byte received Wire.endTransmission(); // stop transmitting delay(50); }Post new comment