design/sys/iop/pcie_common/rtl/dmu_common_ccc_arb.v

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//
// OpenSPARC T2 Processor File: dmu_common_ccc_arb.v
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module dmu_common_ccc_arb
  (
   clk,
   rst_l,

   csr_host_0_req,
   csr_host_1_req,
   csr_host_2_req,
   csr_host_3_req,

   fsm2arb_done,

   csr_host_0_done,
   csr_host_1_done,
   csr_host_2_done,
   csr_host_3_done,

   arb2cdp_sel,
   arb2fsm_valid
   );

// ----------------------------------------------------------------------------
// Parameters
// ----------------------------------------------------------------------------
  parameter     IDLE = 2'b00,           // state machine states
                BUSY = 2'b01,
                DONE = 2'b11;

// ----------------------------------------------------------------------------
// Ports
// ----------------------------------------------------------------------------
  input                                 clk;
  input                                 rst_l;

  input                                 csr_host_0_req;
  input                                 csr_host_1_req;
  input                                 csr_host_2_req;
  input                                 csr_host_3_req;

  input                                 fsm2arb_done;

  output                                csr_host_0_done;
  output                                csr_host_1_done;
  output                                csr_host_2_done;
  output                                csr_host_3_done;

  output [`FIRE_CSR_SRCB_BITS]          arb2cdp_sel;
  output                                arb2fsm_valid;

// ----------------------------------------------------------------------------
// Variables
// ----------------------------------------------------------------------------
  wire [3:0]                            req;

  reg [3:0]                             done, nxt_done;
  reg [1:0]                             grant, new_grant, nxt_grant;
  reg [1:0]                             state, nxt_state;
  reg                                   valid, nxt_valid;

// ----------------------------------------------------------------------------
// Combinational
// ----------------------------------------------------------------------------
// csr host dones
  wire   csr_host_0_done = done[0];
  wire   csr_host_1_done = done[1];
  wire   csr_host_2_done = done[2];
  wire   csr_host_3_done = done[3];

// cdp select and fsm valid
  assign arb2cdp_sel   = grant;
  wire   arb2fsm_valid = valid;

// csr host requests
  assign req[0] = csr_host_0_req;
  assign req[1] = csr_host_1_req;
  assign req[2] = csr_host_2_req;
  assign req[3] = csr_host_3_req;

  wire   any_req = |req;

// round-robin new grant
  always @ (req or grant) begin
    casez ({grant, req}) // synopsys parallel_case
      6'b00_zz1z : new_grant = 2'b01;
      6'b00_z10z : new_grant = 2'b10;
      6'b00_100z : new_grant = 2'b11;
      6'b00_000z : new_grant = 2'b00;

      6'b01_z1zz : new_grant = 2'b10;
      6'b01_10zz : new_grant = 2'b11;
      6'b01_00z1 : new_grant = 2'b00;
      6'b01_00z0 : new_grant = 2'b01;

      6'b10_1zzz : new_grant = 2'b00;
      6'b10_0zz1 : new_grant = 2'b00;
      6'b10_0z10 : new_grant = 2'b00;
      6'b10_0z00 : new_grant = 2'b00;

      6'b11_zzz1 : new_grant = 2'b00;
      6'b11_zz10 : new_grant = 2'b00;
      6'b11_z100 : new_grant = 2'b00;
      6'b11_z000 : new_grant = 2'b00;
    endcase
  end

  always @ (state or any_req or fsm2arb_done) begin
    case (state) // synopsys parallel_case
      IDLE : begin
        if (any_req)      nxt_state = BUSY;
        else              nxt_state = IDLE;
      end
      BUSY : begin
        if (fsm2arb_done) nxt_state = DONE;
        else              nxt_state = BUSY;
      end
      DONE :              nxt_state = IDLE;
      default :           nxt_state = IDLE;
    endcase
  end

  always @ (state or nxt_state or new_grant or grant) begin
    nxt_done  = 0;
    nxt_grant = grant;
    nxt_valid = 0;
    case (state) // synopsys parallel_case
      IDLE : begin
        case (nxt_state) // synopsys parallel_case
          BUSY : begin
            nxt_valid = 1'b1;
            nxt_grant = new_grant;
          end
          default : begin
            nxt_valid = 0;
          end
        endcase
      end
      BUSY : begin
        case (nxt_state) // synopsys parallel_case
          DONE : begin
            nxt_done[grant] = 1'b1;
          end
          default : begin
            nxt_done = 0;
          end
        endcase
      end
      default : begin
        nxt_done  = 0;
        nxt_valid = 0;
      end
    endcase
  end

// ----------------------------------------------------------------------------
// Sequential
// ----------------------------------------------------------------------------
  always  @(posedge clk) begin
    if (!rst_l) begin
      done  <= 0;
      grant <= 0;
      state <= IDLE;
      valid <= 0;
    end
    else begin
      done  <= nxt_done;
      grant <= nxt_grant;
      state <= nxt_state;
      valid <= nxt_valid;
    end
  end

endmodule // dmu_common_ccc_arb