diff --git a/lib/usb_cdcacm.c b/lib/usb_cdcacm.c
index b5b46f3..b866f42 100644
--- a/lib/usb_cdcacm.c
+++ b/lib/usb_cdcacm.c
@@ -39,6 +39,8 @@
 /** maximum packet size for USB data transfer */
 #define USB_DATA_TRANSFER_SIZE 64
 
+volatile bool usb_cdcacm_connecting = false;
+
 static uint8_t usbd_control_buffer[128] = {0}; /**< buffer to be used for control requests */
 static usbd_device *usb_device = NULL; /**< structure holding all the info related to the USB device */
 
@@ -47,7 +49,6 @@ static uint8_t tx_buffer[512] = {0}; /**< ring buffer for data to transmit */
 static volatile uint16_t tx_i = 0; /**< current position if transmitted data */
 static volatile uint16_t tx_used = 0; /**< how much data needs to be transmitted */
 static volatile bool tx_lock = false; /**< if the transmit buffer is currently being written */
-static bool connected = false; /**< is the USB device is connected to a host */
 
 /** USB CDC ACM device descriptor
  *  @note as defined in USB CDC specification section 5
@@ -200,6 +201,7 @@ static const struct usb_interface_descriptor usb_dfu_interface = {
 	.bInterfaceSubClass = 1, /**< DFU interface subclass (not defined in libopencm3 dfu lib) */
 	.bInterfaceProtocol = 1,  /**< runtime protocol (not defined in libopencm3 dfu lib) */
 	.iInterface = 3, /**< the index of the string in the string table that represents interface description */
+
 	.extra = &usb_dfu_functional, /**< point to functional descriptor */
 	.extralen = sizeof(usb_dfu_functional), /**< size of functional descriptor */
 };
@@ -324,7 +326,7 @@ static int usb_cdcacm_control_request(usbd_device *usbd_dev, struct usb_setup_da
 	} else {
 		switch (req->bRequest) {
 			case USB_CDC_REQ_SET_CONTROL_LINE_STATE:
-				connected = req->wValue ? true : false; // check if terminal is open
+				usb_cdcacm_connecting = req->wValue ? true : false; // check if terminal is open
 				//bool dtr = (req->wValue & (1 << 0)) ? true : false;
 				//bool rts = (req->wValue & (1 << 1)) ? true : false;
 				/* this Linux cdc_acm driver requires this to be implemented
@@ -360,6 +362,9 @@ static int usb_cdcacm_control_request(usbd_device *usbd_dev, struct usb_setup_da
 			default:
 				return 0;
 		}
+		if (tx_used>0) { // if buffer is not empty
+			usbd_ep_write_packet(usb_device, 0x82, NULL, 0); // trigger tx callback
+		}
 	}
 	return 1;
 }
@@ -378,7 +383,7 @@ static void usb_cdcacm_data_rx_cb(usbd_device *usbd_dev, uint8_t ep)
 	/* receive data */
 	usb_length = usbd_ep_read_packet(usbd_dev, 0x02, usb_data, sizeof(usb_data));
 	if (usb_length) { // copy received data
-		for (uint16_t i=0; i<usb_length; i++) { // only until buffer is full
+		for (uint16_t i=0; i<usb_length && i<LENGTH(usb_data); i++) { // only until buffer is full
 			user_input_store(usb_data[i]); // store user data
 		}
 	}
@@ -393,7 +398,7 @@ static void usb_cdcacm_data_tx_cb(usbd_device *usbd_dev, uint8_t ep)
 	(void)ep;
 	(void)usbd_dev;
 
-	if (!usbd_dev || !connected || !tx_used) { // verify if we can send and there is something to send
+	if (!usbd_dev || 0==tx_used) { // verify if we can send and there is something to send
 		return;
 	}
 	if (!tx_lock) {
@@ -425,8 +430,6 @@ static void usb_cdcacm_set_config(usbd_device *usbd_dev, uint16_t wValue)
 	
 void usb_cdcacm_setup(void)
 {
-	connected = false; // start with USB not connected
-
 	// initialize USB
 	rcc_periph_reset_pulse(RST_USB); // reset USB peripheral
 	usb_disconnect(); // disconnect to force re-enumeration
@@ -440,11 +443,12 @@ void usb_cdcacm_setup(void)
 	tx_i = 0;
 	tx_used = 0;
 	tx_lock = false; // release lock
+	usb_cdcacm_connecting = false; // clear flag
 }
 
 void usb_cdcacm_putchar(char c)
 {
-	if (!usb_device || !connected) {
+	if (!usb_device) {
 		return;
 	}
 	tx_lock = true; // put lock on transmit buffer
@@ -456,7 +460,7 @@ void usb_cdcacm_putchar(char c)
 		tx_buffer[(tx_i+tx_used)%LENGTH(tx_buffer)] = c; // overwrite old data
 	}
 	tx_lock = false; // release lock on transmit buffer
-	if (tx_used>0) { // to buffer is not empty anymore
+	if (tx_used>0) { // if buffer is not empty anymore
 		usbd_ep_write_packet(usb_device, 0x82, NULL, 0); // trigger tx callback
 	}
 }
diff --git a/lib/usb_cdcacm.h b/lib/usb_cdcacm.h
index d56f489..df1c534 100644
--- a/lib/usb_cdcacm.h
+++ b/lib/usb_cdcacm.h
@@ -19,6 +19,9 @@
  */
 #pragma once
 
+/** flag set to true when user is connected to USB CDC ACM port (e.g. when a terminal is opened) */
+extern volatile bool usb_cdcacm_connecting;
+
 /** setup USB CDC ACM peripheral */
 void usb_cdcacm_setup(void);
 /** send character over USB (non-blocking)