trace: implement timestamp also for ARMv6

Fixes #894.

os/include/arm_v6/trace/timestamp.h

@@ -0,0 +1,33 @@
+/*
+ * \brief  Trace timestamp
+ * \author Stefan Kalkowski
+ * \date   2013-08-20
+ *
+ * Serialized reading of performance counter on ARM.
+ */
+
+/*
+ * Copyright (C) 2013 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__TRACE_TIMESTAMP_H_
+#define _INCLUDE__TRACE_TIMESTAMP_H_
+
+#include <base/fixed_stdint.h>
+
+namespace Genode { namespace Trace {
+
+	typedef uint32_t Timestamp;
+
+	inline Timestamp timestamp()
+	{
+		uint32_t t;
+		asm volatile("mrc p15, 0, %0, c15, c12, 1" : "=r"(t));
+		return t;
+	}
+} }
+
+#endif /* _INCLUDE__TRACE_TIMESTAMP_H_ */