Added files into modelsim folder

ModelSim/instruction_counter.sv

@@ -0,0 +1,21 @@
+`ifndef INSTRUCTION_COUNTER_H
+`define INSTRUCTION_COUNTER_H
+
+module instruction_counter #(parameter width=5)(
+    input logic [0:0] clk, input logic [0:0] we,
+    input logic [2**width-1:0] W,
+    output logic [2**width-1:0] addr
+);
+
+    logic [2**width-1:0] pc;
+    always_ff @(posedge clk) begin
+        if (we) begin
+            pc <= W;
+        end else begin
+            pc <= pc + 4;
+        end
+    end
+
+    assign addr = pc;
+endmodule
+`endif