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

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// OpenSPARC T2 Processor File: pcie_common_dcs_ism.v
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module pcie_common_dcs_ism
  (
   clk,                         // source clock
   rst_l,                       // reset
   csr_rng_cmd,                 // csr ring command
   osm2ism_deq,                 // osm dequeue
   ism2osm_vld,                 // osm valid
   ism2sdp_ds,                  // sdp data select
   ism2sdp_ld                   // sdp load
   );

// ----------------------------------------------------------------------------
// Parameters
// ----------------------------------------------------------------------------
  parameter     QD = 3;                         // queue depth

  parameter     IDLE = 2'b00,                   // state machine states
                LDMS = 2'b01,
                LDLS = 2'b10;

// ----------------------------------------------------------------------------
// Ports
// ----------------------------------------------------------------------------
  input                                 clk;
  input                                 rst_l;
  input  [`FIRE_CSR_CMND_BITS]          csr_rng_cmd;
  input                                 osm2ism_deq;

  output                                ism2osm_vld;
  output [QD-2:0]                       ism2sdp_ds;
  output [QD-1:0]                       ism2sdp_ld;

// ----------------------------------------------------------------------------
// Variables
// ----------------------------------------------------------------------------
  wire                                  ism2osm_vld, deq;

  reg [QD-2:0]                          ism2sdp_ds;
  reg [QD-1:0]                          ism2sdp_ld;
  reg [QD-1:0]                          vld, nxt_vld;
  reg [1:0]                             state, nxt_state;
  reg                                   enq;

  integer i;

// ----------------------------------------------------------------------------
// Zero In Checkers
// ----------------------------------------------------------------------------

  // 0in fifo -enq enq -deq deq -depth QD
  // 0in known_driven -var vld -active rst_l
  // 0in known_driven -var state -active rst_l
  // 0in state_transition -var state -val IDLE -next LDMS
  // 0in state_transition -var state -val LDMS -next LDLS
  // 0in state_transition -var state -val LDLS -next IDLE

// ----------------------------------------------------------------------------
// Combinational
// ----------------------------------------------------------------------------

// valid command
  wire   rng_vld = |csr_rng_cmd;

// next state
  always @ (state or rng_vld) begin
    case (state) // synopsys parallel_case
      IDLE : begin
        if (rng_vld) nxt_state = LDMS;
        else         nxt_state = IDLE;
      end
      LDMS :         nxt_state = LDLS;
      LDLS :         nxt_state = IDLE;
      default :      nxt_state = IDLE;
    endcase
  end

// state outputs
  always @ (state or rng_vld) begin
    case (state) // synopsys parallel_case
      IDLE :    enq = rng_vld;
      LDMS :    enq = 1'b1;
      LDLS :    enq = 1'b1;
      default : enq = 1'b0;
    endcase
  end

// osm valid
  assign ism2osm_vld = vld[0];

// dequeue
  assign deq = osm2ism_deq;

// queue controls
  always @ (rst_l or enq or deq or vld) begin
    for (i = 0; i < QD - 1; i = i + 1) ism2sdp_ds[i] = vld[i+1];
    case ({enq, deq})
      2'b00 : ism2sdp_ld = ~{ QD { rst_l } };
      2'b01 : ism2sdp_ld =  vld;
      2'b10 : ism2sdp_ld = ~vld;
      2'b11 : ism2sdp_ld =  vld;
    endcase
    case ({enq, deq})
      2'b00 : nxt_vld = vld;
      2'b01 : nxt_vld = { 1'b0, vld[QD-1:1] };
      2'b10 : nxt_vld = { vld[QD-2:0], 1'b1 };
      2'b11 : nxt_vld = vld;
    endcase
  end

// ----------------------------------------------------------------------------
// Sequential
// ----------------------------------------------------------------------------
  always @ (posedge clk) begin
    if (!rst_l) begin
      vld   <= 0;
      state <= IDLE;
    end
    else begin
      vld   <= nxt_vld;
      state <= nxt_state;
    end
  end

endmodule // pcie_common_dcs_ism