Added a button press example for l4

Author: benjaminlevine

examples/stm32/l4/nucleo-l476rg/button/Makefile

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+##
+## This file is part of the libopencm3 project.
+##
+## Copyright (C) 2009 Uwe Hermann <[email protected]>
+## Copyright (C) 2016 Benjamin Levine <[email protected]>
+##
+## 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/>.
+##
+
+BINARY = button
+
+LDSCRIPT = ../nucleo-l476rg.ld
+
+include ../../Makefile.include
+

examples/stm32/l4/nucleo-l476rg/button/README.md

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+# README
+
+This example blinks the GREEN LED on the ST Nucleo STM32L476RG eval board.
+
+When you press the 'USER' button, the blinking is faster.
+
+## Board connections
+
+*none required*

examples/stm32/l4/nucleo-l476rg/button/button.c

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+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2009 Uwe Hermann <[email protected]>,
+ * Copyright (C) 2010 Piotr Esden-Tempski <[email protected]>
+ * Copyright (C) 2011 Stephen Caudle <[email protected]>
+ * Copyright (C) 2016 Benjamin Levine <[email protected]>
+ *
+ * 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/stm32/rcc.h>
+#include <libopencm3/stm32/gpio.h>
+
+uint16_t exti_line_state;
+
+/* Set STM32 to 48 MHz. */
+static void clock_setup(void)
+{
+	rcc_clock_setup_pll(&rcc_clock_config[RCC_CLOCK_VRANGE1_HSI16_PLL_48MHZ]);
+}
+
+static void gpio_setup(void)
+{
+	/* Enable GPIOA clock. */
+	rcc_periph_clock_enable(RCC_GPIOA);
+
+	/* Set GPIO5 (in GPIO port A) to 'output push-pull'. */
+    gpio_mode_setup(GPIOA, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO5);
+}
+
+static void button_setup(void)
+{
+	/* Enable GPIOC clock. */
+	rcc_periph_clock_enable(RCC_GPIOC);
+
+	/* Set GPIO13 (in GPIO port C) to 'input open-drain'. */
+	gpio_mode_setup(GPIOC, GPIO_MODE_INPUT, GPIO_PUPD_NONE, GPIO13);
+}
+
+int main(void)
+{
+	int i;
+
+	clock_setup();
+	button_setup();
+	gpio_setup();
+
+	/* Blink the LED (PA5) on the board. */
+	while (1) {
+		gpio_toggle(GPIOA, GPIO5);
+
+		/* Upon button press, blink more quickly. */
+		exti_line_state = GPIOC_IDR;
+		if ((exti_line_state & (1 << 13)) != 0) {
+			for (i = 0; i < 1000000; i++) {	/* Wait a bit. */
+				__asm__("nop");
+			}
+		}
+
+		for (i = 0; i < 500000; i++) {		/* Wait a bit. */
+			__asm__("nop");
+		}
+	}
+
+	return 0;
+}