2 files changed, 105 insertions, 0 deletions
diff --git a/collatz.v b/collatz.v
new file mode 100644
index 0000000..e90c1bd
--- /dev/null
+++ b/collatz.v
@@ -0,0 +1,57 @@
+module collatz (
+  input clk,
+  input rst,
+
+  input wire [15:0] in_start,
+  input wire start_int,
+
+  output reg [15:0] o_count,
+  output finish_int
+);
+
+  localparam IDLE = 0;
+  localparam SPINNING = 1;
+  localparam WAIT_TICK = 2;
+
+  reg [1:0] state = 0;
+  reg [15:0] count = 0;
+  reg [15:0] n = 0;
+
+  wire is_even;
+
+  assign is_even = ~n[0]; 
+  assign finish_int = (n == 1 && state == IDLE);
+
+  always @(posedge start_int) begin
+    if (state == IDLE) begin
+      state <= SPINNING;
+      n <= in_start;
+    end
+  end
+
+  always @(posedge clk or posedge rst) begin
+    if (rst == 1'b1) begin
+      state <= IDLE;
+      count <= 0;
+      n <= 0;
+    end else if (state == IDLE) begin
+      n <= 0;
+    end else if (state == SPINNING) begin
+      if (n <= 1) begin
+        o_count = count;
+        state = WAIT_TICK;
+        // finish_int should be triggered.
+      end else begin
+        if (is_even) begin
+          n <= n >> 1;
+        end else begin
+          n <= n * 3 + 1;
+        end
+        count <= count + 1;
+      end
+    end else if (state == WAIT_TICK) begin
+      state <= IDLE;
+    end
+  end
+
+  endmodule
diff --git a/collatz_tb.v b/collatz_tb.v
new file mode 100644
index 0000000..7419d3f
--- /dev/null
+++ b/collatz_tb.v
@@ -0,0 +1,48 @@
+`timescale 1 ns / 10 ps
+
+module collatz_tb ();
+  reg clk = 0;
+  reg rst = 0;
+
+  wire finish;
+
+  localparam integer DURATION = 10_000;
+
+  always begin
+    #41.667;
+
+    clk = ~ clk;
+  end
+
+  reg [15:0] n = 9;
+  reg start_int;
+
+  wire [15:0] count_out;
+
+  collatz ctz (
+    .clk(clk),
+    .rst(rst),
+    .in_start(n),
+    .start_int(start_int),
+    .o_count(count_out),
+    .finish_int(finish)
+  );
+
+  initial begin
+    #10 rst = 1'b1;
+    #1 rst = 1'b0;
+  end
+
+  initial begin
+    $dumpfile("collatz_tb.vcd");
+    $dumpvars(0, collatz_tb);
+
+    #50 start_int = 1;
+    #10 start_int = 0;
+
+    #(DURATION);
+    $display("Finished!");
+    $finish;
+  end
+
+endmodule