user button on maple mini can be used

global.h

@@ -14,6 +14,10 @@
  */
 /* Copyright (c) 2016 King Kévin <kingkevin@cuvoodoo.info> */
 
+#include <libopencm3/stm32/gpio.h> // GPIO defines
+#include <libopencm3/cm3/nvic.h> // interrupt defines
+#include <libopencm3/stm32/exti.h> // external interrupt defines
+
 /* get the length of an array */
 #define LENGTH(x) (sizeof(x) / sizeof((x)[0]))
 
@@ -22,17 +26,28 @@
 
 /* LED pin */
 #ifdef SYSTEM_BOARD
-/* for system board LED is on pin 11/PA1 */
+/* on system board LED is on pin 11/PA1 */
 #define LED_RCC RCC_GPIOA
 #define LED_PORT GPIOA
 #define LED_PIN	GPIO1
 #elif MAPLE_MINI
-/* for maple mini LED is on pin 19/PB1 */
+/* on maple mini LED is on pin 19/PB1 */
 #define LED_RCC RCC_GPIOB
 #define LED_PORT GPIOB
 #define LED_PIN GPIO1
 #endif
 
+/* user button */
+#ifdef MAPLE_MINI
+/* on maple mini button is on 32/PB8 */
+#define BUTTON_RCC RCC_GPIOB
+#define BUTTON_PORT GPIOB
+#define BUTTON_PIN GPIO8
+#define BUTTON_EXTI EXTI8
+#define BUTTON_IRQ NVIC_EXTI9_5_IRQ
+#define BUTTON_ISR exti9_5_isr
+#endif
+
 /* switch on LED */
 void led_on(void);
 /* switch off LED */

main.c

@@ -26,6 +26,8 @@
 #include <libopencm3/stm32/gpio.h> // general purpose input output library
 #include <libopencm3/cm3/scb.h> // vector table definition
 #include <libopencmsis/core_cm3.h> // Cortex M3 utilities
+#include <libopencm3/cm3/nvic.h> // interrupt utilities
+#include <libopencm3/stm32/exti.h> // external interrupt utilities
 
 /* own libraries */
 #include "global.h" // board definitions
@@ -83,17 +85,26 @@ int main(void)
 	SCB_VTOR = (uint32_t) 0x08002000; // relocate vector table because of the bootloader
 
 	rcc_clock_setup_in_hse_8mhz_out_72mhz(); // use 8 MHz high speed external clock to generate 72 MHz internal clock
+    usart_setup(); // setup USART (for printing)
+    cdcacm_setup(); // setup USB CDC ACM (for printing)
+    setbuf(stdout, NULL); // set standard out buffer to NULL to immediately print   
+    setbuf(stderr, NULL); // set standard error buffer to NULL to immediately print
 
 	// setup LED
-	rcc_periph_clock_enable(LED_RCC); //enable clock for LED
+	rcc_periph_clock_enable(LED_RCC); // enable clock for LED
 	gpio_set_mode(LED_PORT, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, LED_PIN); // set LED pin to 'output push-pull'
 	led_off(); // switch off LED to indicate setup started
 
-	usart_setup(); // setup USART (for printing)
-	cdcacm_setup(); // setup USB CDC ACM (for printing)
-	
-	setbuf(stdout, NULL); // set standard out buffer to NULL to immediately print	
-	setbuf(stderr, NULL); // set standard error buffer to NULL to immediately print
+	// setup button
+#if defined(BUTTON_RCC) && defined(BUTTON_PORT) && defined(BUTTON_PIN) && defined(BUTTON_EXTI) && defined(BUTTON_IRQ)
+	rcc_periph_clock_enable(BUTTON_RCC); // enable clock for button
+	gpio_set_mode(BUTTON_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, BUTTON_PIN); // set button pin to input
+	rcc_periph_clock_enable(RCC_AFIO); // enable alternate function clock for external interrupt
+	exti_select_source(BUTTON_EXTI, BUTTON_PORT); // mask external interrupt of this pin only for this port
+	exti_set_trigger(BUTTON_EXTI, EXTI_TRIGGER_BOTH); // trigger on both edge
+	exti_enable_request(BUTTON_EXTI); // enable external interrupt
+	nvic_enable_irq(BUTTON_IRQ); // enable interrupt
+#endif
 
 	printf("welcome to the STM32F1 CuVoodoo example code\n"); // print welcome message
 	led_on(); // switch on LED to indicate setup completed
@@ -113,3 +124,11 @@ int main(void)
 
 	return 0;
 }
+
+#if defined(BUTTON_ISR) && defined(BUTTON_EXTI)
+void BUTTON_ISR(void)
+{
+	exti_reset_request(BUTTON_EXTI); // reset interrupt
+	led_toggle(); // toggle LED to show the button press has been detected
+}
+#endif