add USB disconnect functionnality for maple mini to force re-enumerate

lib/usb_cdcacm.c

@@ -295,12 +295,24 @@ static void cdcacm_set_config(usbd_device *usbd_dev, uint16_t wValue)
 void cdcacm_setup(void)
 {
 	/* short USB disconnect to force re-enumerate */
+#ifdef SYSTEM_BOARD
+	// pull USB D+ low for a short while
 	rcc_periph_clock_enable(RCC_GPIOA);
 	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO12);
 	gpio_clear(GPIOA, GPIO12);
-	for (uint32_t i = 0; i < 0x1000; i++) {
+	for (uint32_t i = 0; i < 0x8000; i++) {
 		__asm__("nop");
 	}
+#elif MAPLE_MINI
+	// disconnect USB D+ using dedicated DISC line/circuit on PB9
+	rcc_periph_clock_enable(RCC_GPIOB);
+	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO9);
+	gpio_set(GPIOB, GPIO9);
+	for (uint32_t i = 0; i < 0x800; i++) {
+		__asm__("nop");
+	}
+	gpio_clear(GPIOB, GPIO9);
+#endif
 	
 	/* initialize USB */
 	usb_device = usbd_init(&st_usbfs_v1_usb_driver, &device_descriptor, &config, usb_strings, 3, usbd_control_buffer, sizeof(usbd_control_buffer));