Update README and add contrib dir

contrib/tsn/model/clock-fix-precision.h

@@ -0,0 +1,64 @@
+#ifndef FIXPRECISIONCLOCK_H
+#define FIXPRECISIONCLOCK_H
+
+#include "ns3/object.h"
+#include "ns3/nstime.h"
+
+#include "ns3/clock.h"
+
+namespace ns3
+{
+
+  /**
+   * \ingroup tsn
+   * \brief Clock with fix precision.
+   *
+   * This class represents a non realistic clock that have a fix precision
+   * according to the grandmaster time base. It is only use to research purpose
+   * (search of the worst case scenario)
+   *
+   */
+class FixPrecisionClock: public Clock
+{
+  public:
+    /**
+     * \brief Get the TypeId
+     *
+     * \return The TypeId for this class
+     */
+    static TypeId GetTypeId();
+
+    /**
+     * \brief Create a FixPrecisionClock
+     */
+    FixPrecisionClock();
+
+    /**
+     * Destroy a FixPrecisionClock
+     *
+     * This is the destructor for the FixPrecisionClock.
+     */
+    ~FixPrecisionClock() override;
+
+    // Delete copy constructor and assignment operator to avoid misuse
+    FixPrecisionClock& operator=(const FixPrecisionClock&) = delete;
+    FixPrecisionClock(const FixPrecisionClock&) = delete;
+
+    Time GetLocalTime() override;
+    Time GetUncorrectedLocalTime() override;
+    Time GetTimeAt(Time t) override;
+    Time GetDuration(Time t) override;
+
+    void SetRefClock(Ptr<Clock> refClock);
+
+
+  protected:
+
+  private:
+    Time m_precision;
+    Ptr<Clock> m_refClock = nullptr;
+
+};
+
+}
+#endif /* FIXPRECISIONCLOCK_H */