native/platform: flash error led using morse subsystem to indicate no…

… USB host present.

src/platforms/native/platform.c

@@ -40,6 +40,7 @@
 
 static void adc_init(void);
 static void setup_vbus_irq(void);
+static void wait_for_usb_host_config_request(void);
 
 /* This is defined by the linker script */
 extern char vector_table;
@@ -240,6 +241,7 @@ void platform_init(void)
 		aux_serial_init();
 
 	setup_vbus_irq();
+	wait_for_usb_host_config_request();
 }
 
 void platform_nrst_set_val(bool assert)
@@ -485,3 +487,16 @@ static void setup_vbus_irq(void)
 
 	exti15_10_isr();
 }
+
+static void wait_for_usb_host_config_request(void)
+{
+	if (usb_get_config() == 0) {
+		morse("NO USB HOST.", true);
+	}
+
+	/* Wait for completion of USB serial or DFU configuration */
+	while (usb_get_config() == 0) {
+	}
+
+	morse(NULL, false);
+}