diff --git a/lib/usart.c b/lib/usart.c
index 4c862a8..1897df2 100644
--- a/lib/usart.c
+++ b/lib/usart.c
@@ -25,16 +25,17 @@
 #include <libopencm3/stm32/gpio.h> // general purpose input output library
 #include <libopencm3/stm32/usart.h> // universal synchronous asynchronous receiver transmitter library
 #include <libopencm3/cm3/nvic.h> // interrupt handler
+#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
 
 #include "usart.h" // USART header and definitions
 
 /* input and output ring buffer, indexes, and available memory */
-uint8_t rx_buffer[USART_BUFFER] = {0};
-volatile uint8_t rx_i = 0;
-volatile uint8_t rx_used = 0;
-uint8_t tx_buffer[USART_BUFFER] = {0};
-volatile uint8_t tx_i = 0;
-volatile uint8_t tx_used = 0;
+static uint8_t rx_buffer[USART_BUFFER] = {0};
+static volatile uint8_t rx_i = 0;
+static volatile uint8_t rx_used = 0;
+static uint8_t tx_buffer[USART_BUFFER] = {0};
+static volatile uint8_t tx_i = 0;
+static volatile uint8_t tx_used = 0;
 /* show the user how much data received over USART is ready */
 volatile uint8_t usart_received = 0; // same as rx_used, but since the user can write this variable we don't rely on it
 
@@ -79,7 +80,7 @@ void usart_putchar_blocking(char c)
 void usart_flush(void)
 {
 	while (tx_used) { // idle until buffer is empty
-		__asm__("wfi"); // sleep until interrupt
+		__WFI(); // sleep until interrupt
 	}
 	usart_wait_send_ready(USART); // wait until transmit register is empty (transmission might not be complete)
 }
@@ -88,7 +89,7 @@ void usart_flush(void)
 char usart_getchar(void)
 {
 	while (!rx_used) { // idle until data is available
-		__asm__("wfi"); // sleep until interrupt;
+		__WFI(); // sleep until interrupt;
 	}
 	char to_return = rx_buffer[rx_i]; // get the next available character
 	rx_i = (rx_i+1)%sizeof(rx_buffer); // update used buffer
@@ -97,11 +98,11 @@ char usart_getchar(void)
 	return to_return;
 }
 
-/* put character on USART stream (non-blocking using a buffer) */
+/* put character on USART (non-blocking until buffer is full) */
 void usart_putchar_nonblocking(char c)
 {
 	while (tx_used>=sizeof(tx_buffer)) { // idle until buffer has some space
-		__asm__("wfi");
+		__WFI();
 	}
 	tx_buffer[(tx_i+tx_used)%sizeof(tx_buffer)] = c; // put character in buffer
 	tx_used++; // update used buffer
diff --git a/lib/usart.h b/lib/usart.h
index 0fd167e..8911e59 100644
--- a/lib/usart.h
+++ b/lib/usart.h
@@ -25,8 +25,8 @@
 
 /* serial baudrate, in bits per second (with 8N1 8 bits, no parity bit, 1 stop bit settings) */
 #define BAUD 115200
-/* USART RX and TX buffer sizes */
-#define USART_BUFFER 64
+/* RX and TX buffer sizes */
+#define USART_BUFFER 128
 /* show the user how much received is available */
 extern volatile uint8_t usart_received;