stm32l4: add initial soc support for stm32l4

Add the initial SoC support for the STM32L4XX family. The code was
tested on STM32L476RG, but should work on any STM32L4XX currently
available.

This implementation was inspired by the stm32f1x implementation.

Change-Id: Id6670bce0c423617284e8467a9c461531f948e0f
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>

arch/arm/soc/st_stm32/stm32l4/soc.c

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2016 Open-RnD Sp. z o.o.
+ * Copyright (c) 2016 BayLibre, SAS
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * @file
+ * @brief System/hardware module for STM32L4 processor
+ */
+
+#include <nanokernel.h>
+#include <device.h>
+#include <init.h>
+#include <soc.h>
+#include <arch/cpu.h>
+
+/**
+ * @brief Perform basic hardware initialization at boot.
+ *
+ * This needs to be run from the very beginning.
+ * So the init priority has to be 0 (zero).
+ *
+ * @return 0
+ */
+static int stm32l4_init(struct device *arg)
+{
+	uint32_t key;
+
+	ARG_UNUSED(arg);
+
+	key = irq_lock();
+
+	/* Setup the vector table offset register (VTOR),
+	 * which is located at the beginning of flash area.
+	 */
+	_scs_relocate_vector_table((void *)CONFIG_FLASH_BASE_ADDRESS);
+
+	/* Clear all faults */
+	_ScbMemFaultAllFaultsReset();
+	_ScbBusFaultAllFaultsReset();
+	_ScbUsageFaultAllFaultsReset();
+
+	_ScbHardFaultAllFaultsReset();
+
+	/* Install default handler that simply resets the CPU
+	 * if configured in the kernel, NOP otherwise
+	 */
+	NMI_INIT();
+
+	irq_unlock(key);
+
+	/* Update CMSIS SystemCoreClock variable (HCLK) */
+	SystemCoreClock = CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC;
+
+	return 0;
+}
+
+SYS_INIT(stm32l4_init, PRE_KERNEL_1, 0);