Added read ahead buffer

Author: pConst

read_ahead_buf.sv

@@ -0,0 +1,118 @@
+//------------------------------------------------------------------------------
+// fwft_read_ahead_buf.sv
+// published as part of https://github.com/pConst/basic_verilog
+// Konstantin Pavlov, [email protected]
+//------------------------------------------------------------------------------
+
+// INFO ------------------------------------------------------------------------
+// Read ahead buffer
+//
+
+
+/* --- INSTANTIATION TEMPLATE BEGIN ---
+
+read_ahead_buf #(
+  .DATA_W( 32 )
+)(
+  .clk(  ),
+  .anrst(  ),
+
+  // input fifo interface
+  .fifo_r_req(  ),
+  .fifo_r_data(  ),
+  .fifo_empty(  ),
+
+  // output fifo interface
+  .r_req(  ),
+  .r_data(  ),
+  .empty(  )
+);
+
+--- INSTANTIATION TEMPLATE END ---*/
+
+
+module read_ahead_buf #( parameter
+  DATA_W = 32
+)(
+  input clk,               // clock
+  input anrst,             // inverse reset
+
+  // input fifo interface
+  output fifo_r_req,
+  input [DATA_W-1:0] fifo_r_data,
+  input fifo_empty,
+
+  // output fifo interface
+  input r_req,
+  output logic [DATA_W-1:0] r_data,
+  output logic empty
+);
+
+  // buffer initialization flags
+  logic buf_empty = 1'b1;
+
+  // buffer fill request
+  logic buf_fill_req;
+  assign buf_fill_req = ~fifo_empty &&
+                        buf_empty &&
+                        ~buf_fill_req_d1;
+
+  // buffer fill and re-fill cycle
+  logic buf_fill_req_d1 = 1'b0;
+  always_ff @(posedge clk or negedge anrst) begin
+    if( ~anrst ) begin
+      buf_fill_req_d1 <= 1'b0;
+    end else begin
+      buf_fill_req_d1 <= buf_fill_req;
+    end
+  end
+
+  // filtering read requests
+  logic r_req_filt;
+  assign r_req_filt = anrst &&
+                      ~fifo_empty &&
+                      ~buf_empty &&
+                      ~buf_fill_req && r_req;
+
+  logic r_req_rise;
+  logic r_req_fall;
+  edge_detect r_req_ed (
+    .clk( clk ),
+    .nrst( anrst ),
+    .in( r_req_filt ),
+    .rising( r_req_rise ),
+    .falling( r_req_fall ),
+    .both(  )
+  );
+
+  assign fifo_r_req = r_req_filt;
+  assign empty = anrst && fifo_empty && buf_empty;
+
+  // buffer itself
+  logic [DATA_W-1:0] r_data_buf = '0;
+  always_ff @(posedge clk or negedge anrst) begin
+    if( ~anrst ) begin
+      buf_empty = 1'b1;
+    end else begin
+
+      if( buf_fill_req_d1 ) begin
+        r_data_buf[DATA_W-1:0] <= fifo_r_data[DATA_W-1:0];
+        buf_empty = 1'b0;
+      end else if( ~r_req_filt && r_req_fall )  begin
+        r_data_buf[DATA_W-1:0] <= fifo_r_data[DATA_W-1:0];
+      end
+
+    end
+  end
+
+  soft_latch #(
+    .WIDTH( DATA_W )
+  ) r_data_latch (
+    .clk( clk ),
+    .anrst( anrst ),
+    .latch( r_req_filt ),
+    .in( (r_req_rise)?(r_data_buf[DATA_W-1:0]):(fifo_r_data[DATA_W-1:0]) ),
+    .out( r_data[DATA_W-1:0] )
+  );
+
+endmodule