From 69de37cdb25563f6cbd2a3c1a338b1e0dd47b3a4 Mon Sep 17 00:00:00 2001
From: Jan Tuomi <jan@jantuomi.fi>
Date: Tue, 18 Mar 2025 18:38:44 +0200
Subject: Start reworking fpga impl

---
 atk16_fpga/foo.v | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 atk16_fpga/foo.v

(limited to 'atk16_fpga/foo.v')

diff --git a/atk16_fpga/foo.v b/atk16_fpga/foo.v
new file mode 100644
index 0000000..f6ff33c
--- /dev/null
+++ b/atk16_fpga/foo.v
@@ -0,0 +1,106 @@
+// Top-level module
+module foo (
+    LED1,
+    LED2,
+    BUT1,
+    BUT2,
+    SYSCLK
+);
+    output LED1;
+    output LED2;
+    input BUT1;
+    input BUT2;
+    input SYSCLK;
+
+    // 2-bit counter register
+    reg [1:0] val;
+    initial val = 2'b00;
+
+    // Wires for debounced button signals
+    wire db_but1;
+    wire db_but2;
+
+    // Instantiate debounce modules for each button.
+    // Adjust the DEBOUNCE_LIMIT parameter as needed based on SYSCLK frequency.
+    debounce #(
+        .DEBOUNCE_LIMIT(500000)
+    ) debounce_but1 (
+        .clk(SYSCLK),
+        .button(BUT1),
+        .db_out(db_but1)
+    );
+
+    debounce #(
+        .DEBOUNCE_LIMIT(500000)
+    ) debounce_but2 (
+        .clk(SYSCLK),
+        .button(BUT2),
+        .db_out(db_but2)
+    );
+
+    // Edge detection registers to trigger a single count change per button press.
+    reg prev_db_but1;
+    reg prev_db_but2;
+    initial begin
+        prev_db_but1 = 1'b0;
+        prev_db_but2 = 1'b0;
+    end
+
+    // Drive LEDs from the counter bits.
+    assign LED1 = val[0];
+    assign LED2 = val[1];
+
+    // Synchronous logic to detect rising edges and update counter.
+    always @(posedge SYSCLK) begin
+        // If a rising edge is detected on db_but1, increment the counter.
+        if (db_but1 && !prev_db_but1) val <= val + 1;
+        // Else, if a rising edge is detected on db_but2, decrement the counter.
+        else if (db_but2 && !prev_db_but2) val <= val - 1;
+
+        // Store the current debounced states for edge detection on the next clock.
+        prev_db_but1 <= db_but1;
+        prev_db_but2 <= db_but2;
+    end
+
+endmodule
+
+// Debounce module written in plain Verilog.
+module debounce (
+    clk,
+    button,
+    db_out
+);
+    parameter DEBOUNCE_LIMIT = 500000;  // Adjust as needed for your clock frequency.
+    input clk;
+    input button;
+    output db_out;
+    reg db_out;
+
+    reg [31:0] counter;  // Counter width chosen to comfortably count up to DEBOUNCE_LIMIT.
+    reg button_sync;
+
+    initial begin
+        counter     = 32'd0;
+        db_out      = 1'b0;
+        button_sync = 1'b0;
+    end
+
+    always @(posedge clk) begin
+        // First, synchronize the raw button input to the clock domain.
+        button_sync <= button;
+
+        // If the synchronized value equals the debounced output,
+        // reset the counter.
+        if (button_sync == db_out) counter <= 32'd0;
+        else begin
+            // Otherwise, increment the counter.
+            counter <= counter + 1;
+            // If the counter reaches the limit, update the debounced output.
+            if (counter >= DEBOUNCE_LIMIT) begin
+                db_out  <= button_sync;
+                counter <= 32'd0;
+            end
+        end
+    end
+
+endmodule
-- 
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