prio_encode.cpp

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//
// This reference design file, and your use thereof, is subject to and governed
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// License Agreement (either as signed by you or found at www.altera.com).  By
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// accommodation and therefore all warranties, representations or guarantees of 
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/////////////////////////////////////////////////////////////////////////////

//baeckler - 11-14-2006

#include <stdio.h>

int log2 (int n)
{
	int bits = 0;
	while (n)
	{
		n >>= 1;
		bits++;
	}
	return (bits);
}

int main (void)
{
	unsigned int num_ins = 6;
	unsigned int num_outs = log2(num_ins);

	unsigned int num_cases = (1<<num_ins);
	unsigned int n = 0, k = 0;
	unsigned int out_val = 0;

	fprintf (stdout,"//baeckler - 11-14-2006\n");
	fprintf (stdout,"// priority encoder\n");
	fprintf (stdout,"//   no requests - output = 0\n");
	fprintf (stdout,"//   request bit 0 (highest priority) - output = 1\n");
	fprintf (stdout,"//   request bit %d (lowest priority) - output = %d\n",num_ins-1,num_ins);
	fprintf (stdout,"module prio_encode (reqs,out);\n");
	fprintf (stdout,"input [%d:0] reqs;\n",num_ins-1);
	fprintf (stdout,"output [%d:0] out;\n",num_outs-1);
	fprintf (stdout,"reg [%d:0] out;\n\n",num_outs-1);

	fprintf (stdout,"    always @(*) begin\n");
	fprintf (stdout,"      case(reqs)\n");
	
	fprintf (stdout,"        // 0 is special, no reqs\n");
	fprintf (stdout,"        %d'd%d: out = %d;\n\n",num_ins,0,0);		    
	
	for (n=1; n<num_cases; n++)
	{	
		out_val = 1;
		k = n;
		while (k && !(k&1))
		{
			k >>=1;
			out_val += 1;	
		}	
		fprintf (stdout,"        %d'd%d: out = %d;\n",num_ins,n,out_val);		    
	}
	fprintf (stdout,"      endcase\n");
	fprintf (stdout,"    end\n");
	fprintf (stdout,"endmodule\n");
	return (0);
}