Subversion Repositories round_robin_arbiter

//Using Two Simple Priority Arbiters with a Mask - scalable

//author: dongjun_luo@hotmail.com

module round_robin_arbiter (

        rst_an,

        clk,

        req,

        grant

);

parameter N = 4;

input           rst_an;

input           clk;

input   [N-1:0]  req;

output  [N-1:0]  grant;

reg     [N-1:0]  rotate_ptr;

wire    [N-1:0]  mask_req;

wire    [N-1:0]  mask_grant;

wire    [N-1:0]  grant_comb;

reg     [N-1:0]  grant;

wire            no_mask_req;

wire    [N-1:0] nomask_grant;

wire            update_ptr;

genvar i;

// rotate pointer update logic

assign update_ptr = |grant[N-1:0];

always @ (posedge clk or negedge rst_an)

begin

        if (!rst_an)

                rotate_ptr[N-1:0] <= {N{1'b1}};

        else if (update_ptr)

        begin

                // note: N must be at least 2

                rotate_ptr[0] <= grant[N-1];

                rotate_ptr[1] <= grant[N-1] | grant[0];

        end

end

generate

for (i=2;i<N;i=i+1)

always @ (posedge clk or negedge rst_an)

begin

        if (!rst_an)

                rotate_ptr[i] <= 1'b1;

        else if (update_ptr)

                rotate_ptr[i] <= grant[N-1] | (|grant[i-1:0]);

end

endgenerate

// mask grant generation logic

assign mask_req[N-1:0] = req[N-1:0] & rotate_ptr[N-1:0];

assign mask_grant[0] = mask_req[0];

generate

for (i=1;i<N;i=i+1)

        assign mask_grant[i] = (~|mask_req[i-1:0]) & mask_req[i];

endgenerate

// non-mask grant generation logic

assign nomask_grant[0] = req[0];

generate

for (i=1;i<N;i=i+1)

        assign nomask_grant[i] = (~|req[i-1:0]) & req[i];

endgenerate

// grant generation logic

assign no_mask_req = ~|mask_req[N-1:0];

assign grant_comb[N-1:0] = mask_grant[N-1:0] | (nomask_grant[N-1:0] & {N{no_mask_req}});

always @ (posedge clk or negedge rst_an)

begin

        if (!rst_an)    grant[N-1:0] <= {N{1'b0}};

        else            grant[N-1:0] <= grant_comb[N-1:0] & ~grant[N-1:0];

end

endmodule