Arbiter

An arbiter is a digital circuit that controls access to a shared resource by many devices. Each device must request the use of the resource, and the arbiter decides which device gets it, outputting a “grant” signal.

Implementation

module arbiter(r, g, clock, resetn);
	input [3:1] r;
	output [3:1] g;
	input clock, reset;
 
	reg [3:0] y; // current state
	reg [3:0] Y; // next state
	parameter [3:0] s_idle = 4'b0001, s_g1 = 4'b0010, s_g2 = 4'b0100, s_g3 = 4'b1000;
	// encodes so we can use the symbolic name and don't have to type out the full bits
 
	always@(y, r) begin // next-state logic
		case(y)
			s_idle: begin
				if (r[1])
					Y = s_g1;
				else if (r[2])
					Y = s_g2;
				else if (r[3])
					Y = s_g3;
				else
					Y = s_idle;
			end
			s_g1: begin
				if (r[1])
					Y = s_g1;
				else
					Y = s_idle;
			end
			s_g2: begin
				if (r[2])
					Y = s_g2;
				else
					Y = s_idle;
			end
			s_g3: begin
				if (r[3])
					Y = 
			default: Y = s_idle;
		endcase
	end
	// not finished above, below
	always@(posedge clock)
endmodule