Fixes issue #13. Delay reading the button.

README.md

@@ -44,6 +44,8 @@ The bootloader can be built to look for arbitrary patterns, but the default for
 
 The bootloader currently looks for `0x544F` in RTC backup register 1 and `0x4F42` in RTC backup register 0 (together they spell "BOOT" in ASCII).
 
+You can also use a button to stay in bootloader while booting. It's configured using `HAVE_BUTTON` define. If your button has a debounce capacitor, you can use `BUTTON_SAMPLE_DELAY_CYCLES` define to specify how many cycles to wait before sampling the I/O pin, by default it is approximately 20ms in a 72Mhz MCU.
+
 ### WebUSB
 This bootloader implements the draft [WebUSB](https://wicg.github.io/webusb/) specification, which allows web pages to access the bootloader (after presenting the user with a device picker dialog).
 

src/stm32f103/generic/config.h

@@ -33,6 +33,10 @@
 #define HAVE_BUTTON 0
 #endif
 
+#ifndef BUTTON_SAMPLE_DELAY_CYCLES
+#define BUTTON_SAMPLE_DELAY_CYCLES 1440000
+#endif
+
 #ifndef HAVE_USB_PULLUP_CONTROL
 #define HAVE_USB_PULLUP_CONTROL 0
 #endif

src/stm32f103/target_stm32f103.c

@@ -161,6 +161,11 @@ bool target_get_force_bootloader(void) {
     backup_write(BKP0, 0);
 
 #if HAVE_BUTTON
+    /* Wait sometime in case the button has some debounce capacitor */
+    int i;
+    for (i = 0; i < BUTTON_SAMPLE_DELAY_CYCLES; i++) {
+        __asm__("nop");
+    }
     /* Check if the user button is held down */
     if (BUTTON_ACTIVE_HIGH) {
         if (gpio_get(BUTTON_GPIO_PORT, BUTTON_GPIO_PIN)) {