From 7997617e003e10cef96317b77a1d08985d588a83 Mon Sep 17 00:00:00 2001
From: supleed2 <21363892+supleed2@users.noreply.github.com>
Date: Thu, 4 Jun 2020 18:03:46 +0100
Subject: [PATCH] Add stack Verilog file

Uses Last In First Out ordering
---
 LIFOstack.v | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 LIFOstack.v

diff --git a/LIFOstack.v b/LIFOstack.v
new file mode 100644
index 0000000..1a96087
--- /dev/null
+++ b/LIFOstack.v
@@ -0,0 +1,46 @@
+module LIFOstack (Din, clk, en, rst, rw, Dout, empty, full);
+
+input [15:0] Din; // Data being fed to stack
+input clk; // clock signal input
+input en; // disable stack when not in use
+input rst; // reset pin to clear and reinitialise stack
+input rw; // 0: read, 1: write
+
+output reg [15:0] Dout; // Data being pulled from stack
+output reg empty; // goes high to indicate SP is at 0
+output reg full; // goes high to indicate SP is at (slots)
+
+reg [15:0] stack_mem [3:0];
+reg [4:0] SP; // Points to slot to save next value to
+integer i;
+
+always @ (posedge clk) begin
+		if (!en); // if not enabled, ignore this cycle
+		else begin
+				if (rst) begin // if rst is high, clear memory and reset pointers/outputs
+						SP = 4'b0000;
+						empty = 1'b1;
+						Dout = 16'h0000;
+						for (i = 0; i < 16; i = i + 1) begin
+							stack_mem[i] = 16'h0000;
+							end
+					end
+				else begin
+						if (!full && rw) begin // Write when NOT full & Writing
+								stack_mem[SP] = Din; // Store data into current slot
+								SP = SP + 1'b1; // Increment stack pointer to next empty slot
+								full = (SP == 5'b10000) ? 1 : 0; // Stack is full if SP is (slots)
+								empty = 1'b0; // Stack is never empty after a push
+							end
+						else if (!empty && !rw) begin // Read when NOT empty & reading
+								SP = SP - 1'b1; // Decrement stack pointer to last filled slot
+								Dout = stack_mem[SP]; // Output data from last filled slot
+								stack_mem[SP] = 16'h0000; // Clear slot after setting output
+								full = 1'b0; // Stack is never full after a pop
+								empty = (SP == 5'b00000) ? 1 : 0; // Stack is empty if SP is 0
+							end
+					end
+			end
+	end
+
+endmodule