From 3926d7bae115544dcdf11fa4435debd0cfdffa13 Mon Sep 17 00:00:00 2001
From: uvok
Date: Mon, 29 Dec 2025 17:21:58 +0100
Subject: Fix fifo using memory, fix test bench

---
 fifo.tb.v |  6 ++---
 fifo.v    | 79 +++++++++++++++++++++++++++++++++++++++------------------------
 2 files changed, 52 insertions(+), 33 deletions(-)

diff --git a/fifo.tb.v b/fifo.tb.v
index 58fc084..3238eba 100644
--- a/fifo.tb.v
+++ b/fifo.tb.v
@@ -38,14 +38,14 @@ end
 always #10 clk_i = ~clk_i;
 
 initial begin
-  #10
+  #15
 
-  for (integer run = 0; run < 2; run++) begin
+  for (integer run = 1; run < 3; run++) begin
   
     write_i = 1;
     for (integer addr = 0; addr < 10; addr++) begin
 
-      data_i = addr + run;
+      data_i = (run << 4) | addr;
       #20
       ;
     end
diff --git a/fifo.v b/fifo.v
index eaaa8a8..30b963e 100644
--- a/fifo.v
+++ b/fifo.v
@@ -1,5 +1,7 @@
 `timescale 1us/1us
 
+`include "my_mem.v"
+
 module fifo #(
   parameter DATA_WIDTH = 8,
   parameter DATA_DEPTH = 1024
@@ -20,11 +22,36 @@ module fifo #(
 
 );
 
+localparam DATA_DEPTH_BITS = $clog2(DATA_DEPTH);
+
+// the -1 will make sure it fits
+/* verilator lint_off WIDTHTRUNC */
+localparam [DATA_DEPTH_BITS-1:0] MAX_ADDRESS = (DATA_DEPTH - 1);
+
 // need to "count" to number *including* depth
 reg [$clog2(DATA_DEPTH + 1)-1:0] r_count;
-reg [(DATA_WIDTH-1) : 0] r_datastore [(DATA_DEPTH-1) : 0];
-reg [$clog2(DATA_DEPTH)-1:0] r_read_addr;
-reg [$clog2(DATA_DEPTH)-1:0] r_write_addr;
+reg [DATA_DEPTH_BITS-1:0] r_read_addr;
+reg [DATA_DEPTH_BITS-1:0] r_write_addr;
+
+assign empty_o = r_count == 0;
+assign full_o = r_count == DATA_DEPTH;
+
+wire int_wr_en = write_i && !full_o;
+wire int_rd_en = read_i && !empty_o;
+
+my_mem #(
+  .DATA_WIDTH(DATA_WIDTH),
+  .DATA_DEPTH(DATA_DEPTH)
+) fifo_mem (
+  .clk_i(clk_i),
+  .write_en_i(int_wr_en),
+  .read_en_i(int_rd_en),
+  .r_read_addr(r_read_addr),
+  .r_write_addr(r_write_addr),
+
+  .data_i(data_i),
+  .data_o(data_o)
+);
 
 initial begin
   r_count = 0;
@@ -33,38 +60,30 @@ initial begin
 end
 
 always @(posedge clk_i or negedge rst_i) begin
-  if (!rst_i) begin
+  if (!rst_i)
     r_count <= 0;
-    r_read_addr <= 0;
-    r_write_addr <= 0;
-  end else if (write_i && read_i) begin
-    r_count <= r_count + 1;
-    r_datastore[r_write_addr] <= data_i;
+  else if (write_i && read_i)
     // nothing to do
-  end else if (write_i && !full_o) begin
+    // count stays the same
+    ;
+  else if (write_i && !full_o)
     r_count <= r_count + 1;
-    r_datastore[r_write_addr] <= data_i;
-  end else if (read_i && !empty_o) begin
+  else if (read_i && !empty_o)
     r_count <= r_count - 1;
-  end
-
-  if (!rst_i) begin
-  end else if (write_i && !full_o) begin
-    // the_verilator wrongly (???) assumes DATA_DEPTH-1 requires 1 more bit than it does?
-    if ({1'b0, r_write_addr} < (DATA_DEPTH - 1))
-      r_write_addr <= r_write_addr + 1;
-    else
-      r_write_addr <= 0;
-  end else if (read_i && !empty_o) begin
-    // the_verilator wrongly (???) assumes DATA_DEPTH-1 requires 1 more bit than it does?
-    if ({1'b0, r_read_addr} < (DATA_DEPTH - 1))
-      r_read_addr <= r_read_addr + 1;
-    else
-      r_read_addr <= 0;
-  end
 end
 
-assign empty_o = r_count == 0;
-assign full_o = r_count == DATA_DEPTH;
+always @(posedge clk_i or negedge rst_i) begin
+  if (!rst_i)
+    r_read_addr <= 0;
+  else if (read_i && !empty_o)
+    r_read_addr <= (r_read_addr < MAX_ADDRESS) ? (r_read_addr + 1) : 0;
+end
+
+always @(posedge clk_i or negedge rst_i) begin
+  if (!rst_i)
+    r_write_addr <= 0;
+  else if (write_i && !full_o)
+    r_write_addr <= (r_write_addr < MAX_ADDRESS) ? (r_write_addr + 1) : 0;
+end
 
 endmodule
-- 
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