from migen.fhdl import structure as f
from migen.fhdl import verilog

class RoundRobin:
	def __init__(self, n):
		self.n = n
		self.bn = f.BitsFor(self.n-1)
		f.Declare(self, "request", f.BV(self.n))
		f.Declare(self, "grant", f.BV(self.bn))

	def GetFragment(self):
		cases = []
		for i in range(self.n):
			switch = []
			for j in reversed(range(i+1,i+self.n)):
				t = j % self.n
				switch = [f.If(self.request[t],
					[f.Assign(self.grant, f.Constant(t, f.BV(self.bn)))],
					switch)]
			case = f.If(~self.request[i], switch)
			cases.append((f.Constant(i, f.BV(self.bn)), case))
		statement = f.Case(self.grant, cases)
		return f.Fragment(sync=[statement])

r = RoundRobin(5)
frag = r.GetFragment()
print(verilog.Convert(frag, {r.request, r.grant}))

===============

/* Machine-generated using Migen */
module top(
        input sys_clk,
        input sys_rst,
        input [4:0] Inst_request,
        output reg [2:0] Inst_grant
);


always @(posedge sys_clk) begin
        if (sys_rst) begin
                Inst_grant <= 3'd0;
        end else begin
                case (Inst_grant)
                        3'd0: begin
                                if ((~Inst_request[0])) begin
                                        if (Inst_request[1]) begin
                                                Inst_grant <= 3'd1;
                                        end else begin
                                                if (Inst_request[2]) begin
                                                        Inst_grant <= 3'd2;
                                                end else begin
                                                        if (Inst_request[3]) begin
                                                                Inst_grant <= 3'd3;
                                                        end else begin
                                                                if (Inst_request[4]) begin
                                                                        Inst_grant <= 3'd4;
                                                                end
                                                        end
                                                end
                                        end
                                end
                        end
                        3'd1: begin
                                if ((~Inst_request[1])) begin
                                        if (Inst_request[2]) begin
                                                Inst_grant <= 3'd2;
                                        end else begin
                                                if (Inst_request[3]) begin
                                                        Inst_grant <= 3'd3;
                                                end else begin
                                                        if (Inst_request[4]) begin
                                                                Inst_grant <= 3'd4;
                                                        end else begin
                                                                if (Inst_request[0]) begin
                                                                        Inst_grant <= 3'd0;
                                                                end
                                                        end
                                                end
                                        end
                                end
                        end
                        3'd2: begin
                                if ((~Inst_request[2])) begin
                                        if (Inst_request[3]) begin
                                                Inst_grant <= 3'd3;
                                        end else begin
                                                if (Inst_request[4]) begin
                                                        Inst_grant <= 3'd4;
                                                end else begin
                                                        if (Inst_request[0]) begin
                                                                Inst_grant <= 3'd0;
                                                        end else begin
                                                                if (Inst_request[1]) begin
                                                                        Inst_grant <= 3'd1;
                                                                end
                                                        end
                                                end
                                        end
                                end
                        end
                        3'd3: begin
                                if ((~Inst_request[3])) begin
                                        if (Inst_request[4]) begin
                                                Inst_grant <= 3'd4;
                                        end else begin
                                                if (Inst_request[0]) begin
                                                        Inst_grant <= 3'd0;
                                                end else begin
                                                        if (Inst_request[1]) begin
                                                                Inst_grant <= 3'd1;
                                                        end else begin
                                                                if (Inst_request[2]) begin
                                                                        Inst_grant <= 3'd2;
                                                                end
                                                        end
                                                end
                                        end
                                end
                        end
                        3'd4: begin
                                if ((~Inst_request[4])) begin
                                        if (Inst_request[0]) begin
                                                Inst_grant <= 3'd0;
                                        end else begin
                                                if (Inst_request[1]) begin
                                                        Inst_grant <= 3'd1;
                                                end else begin
                                                        if (Inst_request[2]) begin
                                                                Inst_grant <= 3'd2;
                                                        end else begin
                                                                if (Inst_request[3]) begin
                                                                        Inst_grant <= 3'd3;
                                                                end
                                                        end
                                                end
                                        end
                                end
                        end
                endcase
        end
end

endmodule