From 74819c86a2897de899b978e208cbb3677f1f4bbd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Tue, 3 Mar 2015 10:30:35 +0100
Subject: [PATCH] ensure transmission is completed

---
 lib/uart.c | 26 ++++++++++++++------------
 lib/uart.h |  2 +-
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/lib/uart.c b/lib/uart.c
index b0be220..1639394 100644
--- a/lib/uart.c
+++ b/lib/uart.c
@@ -30,31 +30,33 @@ FILE uart_io = FDEV_SETUP_STREAM((int (*)(char, struct __file *)) uart_putchar,
 /* configure serial port */
 void uart_init(void)
 {
-	UBRR0H = UBRRH_VALUE;
-	UBRR0L = UBRRL_VALUE;
+	UBRR0H = UBRRH_VALUE; // set baurate (calculated from BAUD)
+	UBRR0L = UBRRL_VALUE; // set baurate (calculated from BAUD)
 #if USE_2X
-	UCSR0A |= (1<<U2X0);
+	UCSR0A |= (1<<U2X0); // use double speed (set depending on BAUD)
 #else
-	UCSR0A &= ~(1<<U2X0);
+	UCSR0A &= ~(1<<U2X0); // do not use double speed (set depending on BAUD)
 #endif
-	UCSR0C = (1<<UCSZ01)|(1<<UCSZ00); /* 8N1 bit data */
-	UCSR0B = (1<<RXEN0)|(1<<TXEN0);   /* enable RX and TX */
-	UCSR0B |= (1<<RXCIE0); /* enable RX complete interrupt */
+	UCSR0C = (1<<UCSZ01)|(1<<UCSZ00); // 8N1 bit data
+	UCSR0B = (1<<RXEN0)|(1<<TXEN0);   // enable RX and TX
+	UCSR0B |= (1<<RXCIE0); // enable RX complete interrupt
 }
 
 /* put character on UART stream */
 void uart_putchar(char c, FILE *stream)
 {
-	if (c == '\n') {
-		uart_putchar('\r', stream); /* add carrier return before line feed. this is recommended for most UART terminals */
+	if (c == '\n') { // add carrier return before line feed. this is recommended for most UART terminals
+		uart_putchar('\r', stream);
 	}
-	loop_until_bit_is_set(UCSR0A, UDRE0);
-	UDR0 = c;
+	while (!(UCSR0A&(1<<UDRE0))); // wait for transmit register to empty
+	UDR0 = c; // put data in transmit register
+	while (!(UCSR0A&(1<<TXC0))); // wait for transmission to complete (else sleep mode can break it)
+	UCSR0A |= (1<<TXC0); // clear transmit flag
 }
 
 /* get character from UART stream (blocking) */
 char uart_getchar(FILE *stream)
 {
-	loop_until_bit_is_set(UCSR0A, RXC0); /* wait until data exists */
+	while (!(UCSR0A&(1<<RXC0))); // wait until data exists
 	return UDR0;
 }
diff --git a/lib/uart.h b/lib/uart.h
index cae389e..899b2f0 100644
--- a/lib/uart.h
+++ b/lib/uart.h
@@ -26,7 +26,7 @@ FILE uart_io;
 
 /* configure serial port */
 void uart_init(void);
-/* put character on UART stream */
+/* put character on UART stream (blocking) */
 void uart_putchar(char c, FILE *stream);
 /* get character from UART stream (blocking) */
 char uart_getchar(FILE *stream);