=========================================================================
	        README for MULTICAST HELIX PACKET SWITCH
=========================================================================

Overview:
=========

  This example demonstrates a  4x4 multicast  helix packet switch. This 
  example was developed and tested on Solaris2.5.

  The switch uses  a  self routing ring  of shift registers to transfer
  cells from one port to another in a pipelined fashion, resolving output 
  contention and efficiently handling multicast cells. Input and output
  ports have fifo buffers of depth four each. 

  This is a simplified model.

  Following is a block diagram of the switch:

        +-----------------------------------------------------------+
        |     fifo				     fifo	    |
	|    +-------+				     +-------+	    |						    
    IN0 |--->| | | | |-----------+	   +---------| | | | |<-----| IN2						    
        |    +-------+    	 |	   |	     +-------+      |
 	|    fifo	         |	   |	     fifo	    |
	|    +-------+		 |	   |	     +-------+	    |			    
   OUT0 |<---| | | | |<-------+	 |	   |  +----->| | | | |----->| OUT2				    
        |    +-------+        |  V	   V  |	     +-------+      |
        |	            +-----+      +-----+	  	    |
	|                   | R0  |<-----| R2  |	            |
	|	      	    +-----+	 +-----+	   	    |
        |		      |  Shift Reg  ^		            |
	|                     v    Ring     |	                    |
        |	            +-----+      +-----+  		    |
	|                   | R1  |----->| R3  |	            |
	|	   	    +-----+	 +-----+	  	    |
        |    fifo	      ^ |	   ^  |	    fifo	    |
	|    +-------+	      | |	   |  |	    +-------+	    |		    
    IN1 |--->| | | | |--------+	|	   |  +---->| | | | |<------| IN3				    
        |    +-------+          |	   |	    +-------+       |
 	|    fifo	        |	   |	    fifo	    |
	|    +-------+	        |	   |	    +-------+	    |			    
   OUT1 |<---| | | | |<---------+	   +--------| | | | |------>| OUT3				    
        |    +-------+ 				    +-------+	    |
	| 							    |
	+-----------------------------------------------------------+


Input and ouput signals are 16-bit packets with the following structure:


   I<-ad(4)->I<-id(4)->I<---data(8)--->I
   +-----------------------------------+
   | | | | | | | | | | | | | | | | | | | 
   +-----------------------------------+

Input and output ports are of signals of type pkt. For instance:
	...
	sc_in<pkt> in0;
	...

where pkt is a user defined structure in SystemC:

struct pkt {
       sc_int<8> data;
       sc_int<4> id;
       bool dest0;
       bool dest1;
       bool dest2;
       bool dest3;

       inline bool operator == (const pkt& rhs) const
   {
     return (rhs.data == data && rhs.id == id && rhs.dest0 == dest0 && 
     rhs.dest1 == dest1 && rhs.dest2 == dest2 && rhs.dest3 == dest3);
   }
}

Each input port is connected to a sender process. Each output port is connected
to a receiver process. The sender and receiver processes are given distinguish
id numbers during instantiations.

A sender process, writes a random value to data, and sends it to one or more
of the four receivers. Each packet also contains a sender id field. Sender 
processes send packets at random intervals, varying from 1 to 4 units of it's
clock.

A receiver process is activated whenever a packet arrives. It then displays
the contents of the packet and the receiver id.


Simulation:
==========

 Executable can be built using the gmake command. Please make sure that
 the variable "SYSTEMC"  within  the  file Makefile.defs points to your 
 installation of SystemC. The simulation run displays the sequence in 
 which the packets are sent and received along with the contents of the
 packets.

 At the end of the simulation, a report is displayed which shows the 
 total no. of packets received, packets dropped and percentage
 of packets dropped.

 It may be a good idea to direct the simulation outputs to a file and then
 can view the simulation results in that file.
 
 The performance(% packets dropped) depends upon a number of factors:

   - the traffic 
   - fifo buffer size
   - speed of the switch, relative to the activity rates on 
     the input ports