From 3ab99e7747d85b12bbfd429966ec42ade02b2da1 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 28 Oct 2013 21:10:47 +0200
Subject: [PATCH] Expand the serial API and add an asynchronous mode

This breaks any existing code using the API, since the callback macro
isn't available anymore.
---
 common/serial.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++--
 common/serial.h | 13 +++-----
 2 files changed, 85 insertions(+), 10 deletions(-)

diff --git a/common/serial.c b/common/serial.c
index a5e5cae..8874c3e 100644
--- a/common/serial.c
+++ b/common/serial.c
@@ -1,8 +1,23 @@
+#include <avr/interrupt.h>
 #include <avr/io.h>
+#include "ringbuffer.h"
 #include "serial.h"
 
 #define BIT(n) (1<<(n))
 
+#ifndef SERIAL_BUFSIZE
+#define SERIAL_BUFSIZE 16
+#endif
+
+#ifdef SERIAL_ASYNC
+static RINGBUFFER(rx, SERIAL_BUFSIZE);
+static RINGBUFFER(tx, SERIAL_BUFSIZE);
+static uint8_t rx_overrun;
+#define INTERRUPTS BIT(RXCIE0)
+#else
+#define INTERRUPTS 0
+#endif
+
 void serial_init(uint16_t baud)
 {
 	DDRD = (DDRD&~0x03) | 0x02;
@@ -13,11 +28,74 @@ void serial_init(uint16_t baud)
 	UBRR0L = baud;
 	UCSR0A = 0;
 	UCSR0C = BIT(UCSZ00) | BIT(UCSZ01);  // 8N1
-	UCSR0B = BIT(RXEN0) | BIT(TXEN0) | BIT(RXCIE0);
+	UCSR0B = BIT(RXEN0) | BIT(TXEN0) | INTERRUPTS;
+}
+
+uint8_t serial_read()
+{
+#ifdef SERIAL_ASYNC
+	return ringbuffer_blocking_pop(rx);
+#else
+	while(!(UCSR0A&BIT(RXC0))) ;
+	return UDR0;
+#endif
+}
+
+uint8_t serial_read_available()
+{
+#ifdef SERIAL_ASYNC
+	return ringbuffer_fill(rx);
+#else
+	return (UCSR0A&BIT(RXC0))!=0;
+#endif
+}
+
+uint8_t serial_read_overrun()
+{
+#ifdef SERIAL_ASYNC
+	uint8_t o = rx_overrun;
+	rx_overrun = 0;
+	return o;
+#else
+	return (UCSR0A&BIT(DOR0))!=0;
+#endif
 }
 
 void serial_write(uint8_t c)
 {
-	while(!(UCSR0A&(1<<UDRE0))) ;
+#ifdef SERIAL_ASYNC
+	ringbuffer_blocking_push(tx, c);
+	UCSR0B |= BIT(UDRIE0);
+#else
+	while(!(UCSR0A&BIT(UDRE0))) ;
 	UDR0 = c;
+#endif
+}
+
+uint8_t serial_write_space()
+{
+#ifdef SERIAL_ASYNC
+	return ringbuffer_space(tx);
+#else
+	return (UCSR0A&BIT(UDRE0))!=0;
+#endif
+}
+
+#ifdef SERIAL_ASYNC
+ISR(USART_UDRE_vect)
+{
+	if(ringbuffer_fill(tx))
+		UDR0 = ringbuffer_pop(tx);
+	else
+		UCSR0B &= ~BIT(UDRIE0);
+}
+
+ISR(USART_RX_vect)
+{
+	uint8_t c = UDR0;
+	if(!ringbuffer_space(rx))
+		rx_overrun = 1;
+	else
+		ringbuffer_push(rx, c);
 }
+#endif
diff --git a/common/serial.h b/common/serial.h
index 04ea50b..f5d5987 100644
--- a/common/serial.h
+++ b/common/serial.h
@@ -1,16 +1,13 @@
 #ifndef SERIAL_H_
 #define SERIAL_H_
 
-#include <avr/interrupt.h>
-
-#define SERIAL_SET_CALLBACK(f) \
-	ISR(USART_RX_vect) \
-	{ \
-		char c = UDR0; \
-		f(c); \
-	}
+#include <stdint.h>
 
 void serial_init(uint16_t);
+uint8_t serial_read();
+uint8_t serial_read_available();
+uint8_t serial_read_overrun();
 void serial_write(uint8_t);
+uint8_t serial_write_space();
 
 #endif
-- 
2.45.2