Subversion Repositories srdydrdy_lib

//----------------------------------------------------------------------

// Srdy/Drdy FIFO Tail "B"

//

// Building block for FIFOs.  The "B" (big) FIFO is design for larger FIFOs

// based around memories, with sizes that may not be a power of 2.

//

// The bound inputs allow multiple FIFO controllers to share a single

// memory.  The enable input is for arbitration between multiple FIFO

// controllers, or between the fifo head and tail controllers on a

// single port memory.

//

// The commit parameter enables read/commit behavior.  This creates

// two read pointers, one which is used for reading from memory and

// a commit pointer which is sent to the head block.  The abort behavior

// has a 3-cycle performance penalty due to pipeline flush.

//

// The FIFO tail assumes a memory with one-cycle read latency, and

// has output buffering to compensate for this.

//

// Naming convention: c = consumer, p = producer, i = internal interface

//----------------------------------------------------------------------

// Author: Guy Hutchison

//

// This block is uncopyrighted and released into the public domain.

//----------------------------------------------------------------------

// Clocking statement for synchronous blocks.  Default is for

// posedge clocking and positive async reset

`ifndef SDLIB_CLOCKING

 `define SDLIB_CLOCKING posedge clk or posedge reset

`endif

// delay unit for nonblocking assigns, default is to #1

`ifndef SDLIB_DELAY

 `define SDLIB_DELAY #1

`endif

module sd_fifo_tail_b

  #(parameter width=8,

    parameter depth=16,

    parameter commit=0,

    parameter asz=$clog2(depth))

    (

     input       clk,

     input       reset,

     input       enable,

     input [asz-1:0]      bound_low,

     input [asz-1:0]      bound_high,

     output reg [asz-1:0]   cur_rdptr,

     output reg [asz-1:0]   com_rdptr,

     input  [asz-1:0]       wrptr,

     output reg           mem_re,

     output reg [asz:0]   usage,

     output               p_srdy,

     input                p_drdy,

     input                p_commit,

     input                p_abort,

     input [width-1:0]    mem_rd_data,

     output [width-1:0]   p_data

     );

  reg [asz-1:0]           nxt_cur_rdptr;

  reg [asz-1:0]           cur_rdptr_p1;

  reg                   empty, full;

  reg                   nxt_irdy;

  reg [width-1:0]       hold_a, hold_b;

  reg                   valid_a, valid_b;

  reg                   prev_re;

  reg [asz:0]           tmp_usage;

  reg [asz:0]           fifo_size;

  wire                  rbuf1_drdy;

  wire                  ip_srdy, ip_drdy;

  wire [width-1:0]       ip_data;

  // Stage 1 -- Read pipeline

  // issue a read if:

  //   1) we are enabled

  //   2) valid_a is 0, OR

  //   3) valid_b is 0, OR

  //   4) valid_a && valid_b && trdy

  always @*

    begin

      if (cur_rdptr[asz-1:0] == (bound_high))

        begin

          cur_rdptr_p1[asz-1:0] = bound_low;

        end

      else

        cur_rdptr_p1 = cur_rdptr + 1;

      empty = (wrptr == cur_rdptr);

      if (commit && p_abort)

        begin

          nxt_cur_rdptr = com_rdptr;

          mem_re = 0;

        end

//      else if (enable & !empty & (!valid_a | (!prev_re & !valid_b) | 

//                             (valid_a & valid_b & p_drdy)))

      else if (enable & !empty & ip_drdy)

        begin

          nxt_cur_rdptr = cur_rdptr_p1;

          mem_re = 1;

        end

      else

        begin

          nxt_cur_rdptr = cur_rdptr;

          mem_re = 0;

        end // else: !if(enable & !empty & (!valid_a | !valid_b |...

      fifo_size = (bound_high - bound_low + 1);

      tmp_usage = wrptr[asz-1:0] - cur_rdptr[asz-1:0];

      if (~tmp_usage[asz])

        usage = tmp_usage[asz-1:0];

      else

        usage = fifo_size - (cur_rdptr[asz-1:0] - wrptr[asz-1:0]);

    end

  always @(posedge clk)

    begin

      if (reset)

        cur_rdptr <= `SDLIB_DELAY bound_low;

      else

        cur_rdptr <= `SDLIB_DELAY nxt_cur_rdptr;

    end

  generate

    if (commit == 1)

      begin : gen_s0

        reg [asz-1:0]  rdaddr_s0, rdaddr_a, rdaddr_b;

        reg [asz-1:0]  nxt_com_rdptr;

        always @(posedge clk)

          begin

            if (reset)

              com_rdptr <= `SDLIB_DELAY bound_low;

            else

              com_rdptr <= `SDLIB_DELAY nxt_com_rdptr;

            if (mem_re)

              rdaddr_s0 <= `SDLIB_DELAY cur_rdptr;

          end

      end

    else

      begin : gen_ns0

        always @*

          com_rdptr = cur_rdptr;

      end

  endgenerate

  // Stage 2 -- read buffering

  always @(`SDLIB_CLOCKING)

    begin

      if (reset)

        begin

          prev_re <= `SDLIB_DELAY 0;

        end

      else

        begin

          if (commit && p_abort)

            prev_re <= `SDLIB_DELAY 0;

          else

            prev_re <= `SDLIB_DELAY mem_re;

        end // else: !if(reset)

    end // always @ (`SDLIB_CLOCKING)

  generate

    if (commit == 1)

      begin

        wire [asz-1:0] ip_rdaddr, p_rdaddr;

        sd_input #(asz+width) rbuf1

          (.clk (clk), .reset (p_abort | reset),

           .c_srdy (prev_re),

           .c_drdy (rbuf1_drdy),

           .c_data ({rdaddr_s0,mem_rd_data}),

           .ip_srdy (ip_srdy), .ip_drdy (ip_drdy),

           .ip_data ({ip_rdaddr,ip_data}));

        sd_output #(asz+width) rbuf2

          (.clk (clk), .reset (p_abort | reset),

           .ic_srdy (ip_srdy),

           .ic_drdy (ip_drdy),

           .ic_data ({ip_rdaddr,ip_data}),

           .p_srdy (p_srdy), .p_drdy (p_drdy),

           .p_data ({p_rdaddr,p_data}));

        always @*

          begin

            if (p_commit)

              nxt_com_rdptr = p_rdaddr;

            else

              nxt_com_rdptr = com_rdptr;

          end

      end // if (commit == 1)

    else

      begin

        sd_input #(width) rbuf1

          (.clk (clk), .reset (p_abort | reset),

           .c_srdy (prev_re),

           .c_drdy (rbuf1_drdy),

           .c_data (mem_rd_data),

           .ip_srdy (ip_srdy), .ip_drdy (ip_drdy),

           .ip_data (ip_data));

        sd_output #(width) rbuf2

          (.clk (clk), .reset (p_abort | reset),

           .ic_srdy (ip_srdy),

           .ic_drdy (ip_drdy),

           .ic_data (ip_data),

           .p_srdy (p_srdy), .p_drdy (p_drdy),

           .p_data (p_data));

      end // else: !if(commit == 1)

  endgenerate

endmodule // it_fifo