fpga: lib: add glitch free mux module

Original-commit: de3b48e89f2f9711b4b97c080d5c35baba45f573

lib/control/Makefile.srcs

@@ -61,4 +61,5 @@ map/axis_muxed_kv_map.v \
 axil_ctrlport_master.v\
 handshake.v\
 ctrlport_to_regport.v \
+glitch_free_mux.v \
 ))

lib/control/glitch_free_mux.v

@@ -0,0 +1,29 @@
+//
+// Copyright 2020 Ettus Research, a National Instruments Brand
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+//
+// Module: glitch_free_mux
+//
+// Description:
+//   This module implements a 2:1 mux in a LUT explicitly to avoid glitches
+//   which can be introduced by unexpected Vivado synthesis.
+//
+
+module glitch_free_mux (
+  input  wire select,
+  input  wire signal0,
+  input  wire signal1,
+  output wire muxed_signal
+);
+
+  (* dont_touch = "TRUE" *) LUT3 #(
+    .INIT(8'hCA) // Specify LUT Contents. O = ~I2&I0 | I2&I1
+  ) mux_out_i (
+    .O (muxed_signal), // LUT general output. Mux output
+    .I0(signal0),      // LUT input. Input 1
+    .I1(signal1),      // LUT input. Input 2
+    .I2(select)        // LUT input. Select bit
+  );
+
+endmodule