Update main.c -reduce chance of becoming stuck in bootloader

Added grace period with accumulation limit into checkForSignal() to reduce chance of becoming stuck in bootloader on devices that boot with signal pin pulled high.

Fixed and enhanced determination comments.

bootloader/main.c

@@ -748,20 +748,23 @@ static void update_EEPROM()
 }
 #endif // UPDATE_EEPROM_ENABLE
 
+#define low_pin_count_threshold 450		// count signal pin is low before determining jump to main firmware
+#define pull_down_pin_count_interations 4000		// greater interations extend grace period for input devices booting with signal pin high
 static void checkForSignal()
 {
     gpio_mode_set_input(input_pin, GPIO_PULL_DOWN);
 
     delayMicroseconds(500);
 
-    for(int i = 0 ; i < 500; i ++){
+    for(int i = 0 ; i < pull_down_pin_count_interations ; i ++){
 	if(!gpio_read(input_pin)){
 	    low_pin_count++;
         }
 
 	delayMicroseconds(10);
+	if (low_pin_count > low_pin_count_threshold) i = pull_down_pin_count_interations ;		// end for loop if low_pin_count_threshold has already been exceeded
     }
-    if (low_pin_count > 450) {
+    if (low_pin_count > low_pin_count_threshold) {		// pulled low & majority stayed low - jump to application
 #if CHECK_SOFTWARE_RESET
         if (!bl_was_software_reset()) {
 	    jump();
@@ -784,7 +787,7 @@ static void checkForSignal()
 	delayMicroseconds(10);
     }
     if (low_pin_count == 0) {
-	return;           // all high while pin is pulled low, bootloader signal
+	return;		// pulled high & never low in history - stay in bootloader only
     }
 
     low_pin_count = 0;
@@ -802,7 +805,7 @@ static void checkForSignal()
     }
 
     if (low_pin_count > 0) {
-	jump();
+	jump();		// floating & low at least once - jump to application
     }
 }