[CM3] Add register definitions for Debug Watch Trace point.

Add provision functions for the use of CPU counter as a high-resolution timer for code benchmarking purposes

lib/cm3/dwt.c

@@ -0,0 +1,77 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Frantisek Burian <BuFran@seznam.cz>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/cm3/scs.h>
+#include <libopencm3/cm3/dwt.h>
+
+/*---------------------------------------------------------------------------*/
+/** @brief DebugTrace Enable the CPU cycle counter
+ *
+ * This function will try to enable the CPU cycle counter that is intended for
+ * benchmarking performance of the code. If function fails, the cycle counter
+ * isn't available on this architecture.
+ *
+ * @returnd true, if success
+ */
+bool dwt_enable_cycle_counter(void)
+{
+#if defined(__ARM_ARCH_6M__)
+	return false;			/* Not supported on ARMv6M */
+#endif /* defined(__ARM_ARCH_6M__) */
+
+#if defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__)
+	/* Note TRCENA is for 7M and above*/
+	SCS_DEMCR |= SCS_DEMCR_TRCENA; 
+	if (DWT_CTRL & DWT_CTRL_NOCYCCNT) {
+		return false;		/* Not supported in implementation */
+	}
+
+	DWT_CYCCNT = 0;
+	DWT_CTRL |= DWT_CTRL_CYCCNTENA;
+	return true;
+#endif /* defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__) */
+
+	/* not supported on other architectures */
+	return false;
+}
+/*---------------------------------------------------------------------------*/
+/** @brief DebugTrace Read the CPU cycle counter
+ *
+ * This function reads the core cycle counter if it is enabled. It is the
+ * fastest clock running on the system.
+ *
+ * @note The CPU cycle counter must be enabled by @ref dwt_enable_cycle_counter
+ *
+ * @returns 0 if cycle counter is not supported or enabled, the cycle counter
+ * value otherwise.
+ */
+uint32_t dwt_read_cycle_counter(void)
+{
+#if defined(__ARM_ARCH_6M__)
+	return 0;		/* Not supported on ARMv6M */
+#endif /* defined(__ARM_ARCH_6M__) */
+
+#if defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__)
+	if (DWT_CTRL & DWT_CTRL_CYCCNTENA) {
+		return DWT_CYCCNT;
+	} else {
+		return 0;		/* not supported or enabled */
+	}
+#endif /* defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__) */
+}