diff --git a/samples/subsys/usb/cdc_acm_composite/prj.conf b/samples/subsys/usb/cdc_acm_composite/prj.conf
index a1f9d4ddd2e..cde468e5dad 100644
--- a/samples/subsys/usb/cdc_acm_composite/prj.conf
+++ b/samples/subsys/usb/cdc_acm_composite/prj.conf
@@ -11,6 +11,7 @@ CONFIG_USB_DEVICE_PRODUCT="Zephyr CDC ACM sample"
 CONFIG_USB_COMPOSITE_DEVICE=y
 CONFIG_USB_CDC_ACM=y
 CONFIG_USB_CDC_ACM_DEVICE_COUNT=2
+CONFIG_USB_CDC_ACM_RINGBUF_SIZE=512
 
 CONFIG_USB_DEVICE_LOG_LEVEL_ERR=y
 CONFIG_USB_DRIVER_LOG_LEVEL_ERR=y
diff --git a/samples/subsys/usb/cdc_acm_composite/src/main.c b/samples/subsys/usb/cdc_acm_composite/src/main.c
index 89d7f2a916d..f012339fb41 100644
--- a/samples/subsys/usb/cdc_acm_composite/src/main.c
+++ b/samples/subsys/usb/cdc_acm_composite/src/main.c
@@ -17,39 +17,71 @@
 #include <device.h>
 #include <uart.h>
 #include <zephyr.h>
+#include <ring_buffer.h>
 
-static const char *banner = "Send characters to another UART device\r\n";
+#include <logging/log.h>
+LOG_MODULE_REGISTER(cdc_acm_composite, CONFIG_LOG_DEFAULT_LEVEL);
+
+#define RING_BUF_SIZE	(64 * 2)
+
+u8_t buffer0[RING_BUF_SIZE];
+u8_t buffer1[RING_BUF_SIZE];
 
 static struct serial_data {
 	struct device *dev;
 	struct device *peer;
+	struct serial_data *peer_data;
+	struct ring_buf ringbuf;
 } peers[2];
 
 static void interrupt_handler(void *user_data)
 {
-	const struct serial_data *dev_data = user_data;
+	struct serial_data *dev_data = user_data;
 	struct device *dev = dev_data->dev;
 
+
 	while (uart_irq_update(dev) && uart_irq_is_pending(dev)) {
 		struct device *peer = dev_data->peer;
-		u8_t byte;
 
-		if (!uart_irq_rx_ready(dev)) {
-			break;
+		LOG_DBG("dev %p dev_data %p", dev, dev_data);
+
+		if (uart_irq_rx_ready(dev)) {
+			u8_t buf[64];
+			size_t read, wrote;
+			struct ring_buf *ringbuf =
+					&dev_data->peer_data->ringbuf;
+
+			read = uart_fifo_read(dev, buf, sizeof(buf));
+			if (read) {
+				wrote = ring_buf_put(ringbuf, buf, read);
+				if (wrote < read) {
+					LOG_ERR("Drop %u bytes", read - wrote);
+				}
+
+				uart_irq_tx_enable(dev_data->peer);
+
+				LOG_DBG("dev %p -> dev %p send %u bytes",
+					dev, peer, wrote);
+			}
 		}
 
-		uart_fifo_read(dev, &byte, sizeof(byte));
-		uart_poll_out(peer, byte);
+		if (uart_irq_tx_ready(dev)) {
+			u8_t buf[64];
+			size_t wrote, len;
 
-		printk("dev %p -> dev %p Sent byte %c\n", dev, peer, byte);
+			len = ring_buf_get(&dev_data->ringbuf, buf,
+					   sizeof(buf));
+			if (!len) {
+				LOG_DBG("dev %p TX buffer empty", dev);
+				uart_irq_tx_disable(dev);
+			} else {
+				wrote = uart_fifo_fill(dev, buf, len);
+				LOG_DBG("dev %p wrote len %d", dev, wrote);
+			}
+		}
 	}
 }
 
-static void write_data(struct device *dev, const char *buf, int len)
-{
-	uart_fifo_fill(dev, (const u8_t *)buf, len);
-}
-
 static void uart_line_set(struct device *dev)
 {
 	u32_t baudrate;
@@ -58,12 +90,12 @@ static void uart_line_set(struct device *dev)
 	/* They are optional, we use them to test the interrupt endpoint */
 	ret = uart_line_ctrl_set(dev, LINE_CTRL_DCD, 1);
 	if (ret) {
-		printf("Failed to set DCD, ret code %d\n", ret);
+		LOG_DBG("Failed to set DCD, ret code %d", ret);
 	}
 
 	ret = uart_line_ctrl_set(dev, LINE_CTRL_DSR, 1);
 	if (ret) {
-		printf("Failed to set DSR, ret code %d\n", ret);
+		LOG_DBG("Failed to set DSR, ret code %d", ret);
 	}
 
 	/* Wait 1 sec for the host to do all settings */
@@ -71,9 +103,9 @@ static void uart_line_set(struct device *dev)
 
 	ret = uart_line_ctrl_get(dev, LINE_CTRL_BAUD_RATE, &baudrate);
 	if (ret) {
-		printf("Failed to get baudrate, ret code %d\n", ret);
+		LOG_DBG("Failed to get baudrate, ret code %d", ret);
 	} else {
-		printf("Baudrate detected: %d\n", baudrate);
+		LOG_DBG("Baudrate detected: %d", baudrate);
 	}
 }
 
@@ -86,17 +118,17 @@ void main(void)
 
 	dev0 = device_get_binding("CDC_ACM_0");
 	if (!dev0) {
-		printf("CDC_ACM_0 device not found\n");
+		LOG_DBG("CDC_ACM_0 device not found");
 		return;
 	}
 
 	dev1 = device_get_binding("CDC_ACM_1");
 	if (!dev1) {
-		printf("CDC_ACM_1 device not found\n");
+		LOG_DBG("CDC_ACM_1 device not found");
 		return;
 	}
 
-	printf("Wait for DTR\n");
+	LOG_DBG("Wait for DTR");
 
 	while (1) {
 		uart_line_ctrl_get(dev0, LINE_CTRL_DTR, &dtr);
@@ -116,23 +148,24 @@ void main(void)
 		k_sleep(100);
 	}
 
-	printf("DTR set, start test\n");
+	LOG_DBG("DTR set, start test");
 
 	uart_line_set(dev0);
 	uart_line_set(dev1);
 
 	dev_data0->dev = dev0;
 	dev_data0->peer = dev1;
+	dev_data0->peer_data = dev_data1;
+	ring_buf_init(&dev_data0->ringbuf, sizeof(buffer0), buffer0);
 
 	dev_data1->dev = dev1;
 	dev_data1->peer = dev0;
+	dev_data1->peer_data = dev_data0;
+	ring_buf_init(&dev_data1->ringbuf, sizeof(buffer1), buffer1);
 
 	uart_irq_callback_user_data_set(dev0, interrupt_handler, dev_data0);
 	uart_irq_callback_user_data_set(dev1, interrupt_handler, dev_data1);
 
-	write_data(dev0, banner, strlen(banner));
-	write_data(dev1, banner, strlen(banner));
-
 	/* Enable rx interrupts */
 	uart_irq_rx_enable(dev0);
 	uart_irq_rx_enable(dev1);