1 files changed, 217 insertions, 0 deletions
diff --git a/avr/serial.c b/avr/serial.c
new file mode 100644
index 0000000..4b3cd42
--- /dev/null
+++ b/avr/serial.c
@@ -0,0 +1,217 @@
+/*
+ */
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/atomic.h>
+#include <errno.h>
+#include <stdio.h>
+
+#include "serial.h"
+
+
+static int _write(char c, FILE *stream);
+static FILE mystdout = FDEV_SETUP_STREAM(_write, 
+		NULL, _FDEV_SETUP_WRITE);
+
+#define CTL_S	('S'-'@')		/* DC3 (Stop) */
+#define CTL_Q	('Q'-'@')		/* DC1 (Start) */
+
+typedef enum {
+	IDLE,
+	ACTIVE,
+	REQ_STOP,
+	REQ_CONT,
+	STOPPED
+} xmit_stat_t;
+
+
+static volatile uint8_t stat_tx;
+static volatile uint8_t stat_rx;
+
+
+struct ring {
+	uint8_t *data;
+	uint_fast8_t mask;
+	volatile uint_fast8_t begin;
+	volatile uint_fast8_t end;
+};
+
+
+#define BUFFER_SIZE 256
+
+#if ((BUFFER_SIZE-1) & BUFFER_SIZE)
+# error: BUFFER_SIZE not power of 2
+#endif
+
+#if ((BUFFER_SIZE) > 256)
+# error: BUFFER_SIZE 
+#endif
+
+struct ring rx_ring;
+struct ring tx_ring;
+uint8_t rx_ring_buffer[BUFFER_SIZE];
+uint8_t tx_ring_buffer[BUFFER_SIZE];
+
+
+static void ring_init(struct ring *ring, uint8_t *buf, int size)
+{
+	ring->data = buf;
+	ring->mask = (size-1) & 0xff;
+	ring->begin = 0;
+	ring->end = 0;
+}
+
+static int ring_write_ch(struct ring *ring, uint8_t ch)
+{
+	uint_fast8_t ep = (ring->end + 1) & ring->mask;
+
+	if ((ep) != ring->begin) {
+		ring->data[ring->end] = ch;
+		ring->end = ep;
+		return 1;
+	}
+
+	return -1;
+}
+
+#if 0
+static int ring_write(struct ring *ring, uint8_t *data, int size)
+{
+	int i;
+
+	for (i = 0; i < size; i++) {
+		if (ring_write_ch(ring, data[i]) < 0)
+			return -i;
+	}
+
+	return i;
+}
+#endif
+
+static int ring_read_ch(struct ring *ring)
+{
+	int ret = -1;
+	uint_fast8_t i = ring->begin;
+
+	if (i != ring->end) {
+		ret = ring->data[i];
+		ring->begin = (i +1) & ring->mask;
+	}
+
+	return ret;
+}
+
+
+static int_fast8_t ring_is_empty(struct ring *ring)
+{
+	return ring->begin == ring->end;
+}
+
+
+/* Initialize UART */
+
+void usart0_setup(void) {
+
+	ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+
+		PRR0 &= ~_BV(PRUSART0);
+		UCSR0B = 0;
+
+		/* Initialize ring buffers. */
+		ring_init(&rx_ring, rx_ring_buffer, BUFFER_SIZE);
+		ring_init(&tx_ring, tx_ring_buffer, BUFFER_SIZE);
+
+		stat_tx = ACTIVE;
+		stat_rx = ACTIVE;
+
+		UCSR0A = _BV(U2X0);
+		UBRR0L = F_CPU / BAUD / 8 - 1;
+		UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
+		UCSR0C = 3 << UCSZ00;
+	};
+}
+
+
+
+/* UART RXC interrupt */
+
+ISR(USART0_RX_vect)
+{
+	uint8_t d;
+
+	d = UDR0;
+
+	switch (d) {
+	case CTL_S:
+		stat_tx = REQ_STOP;
+		break;
+	case CTL_Q:
+		if ((stat_tx == STOPPED) || stat_tx == REQ_STOP) {
+			UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0) | _BV(UDRIE0);
+			stat_tx = ACTIVE;
+		}
+		break;
+	default:
+		ring_write_ch(&rx_ring, d);
+		break;
+	}
+}
+
+/* UART UDRE interrupt */
+
+ISR(USART0_UDRE_vect)
+{
+	uint8_t s;
+
+	s = !ring_is_empty(&tx_ring);
+	if ((s == 0) || (stat_tx != ACTIVE)) {
+		UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0);
+		if (s)
+			stat_tx = STOPPED;
+	} else {
+		UDR0 = ring_read_ch(&tx_ring);
+	}
+}
+
+
+
+/*--------------------------------------------------------------------------*/
+
+void serial_setup(void)
+{
+	stdout = &mystdout;
+	usart0_setup();
+}
+
+/*--------------------------------------------------------------------------*/
+
+int _write(char c, FILE *stream)
+{
+	(void) stream;
+
+	if (c == '\n')
+		serial_putc('\r');
+	serial_putc(c);
+
+	return 0;
+}
+
+int serial_getc(void)
+{
+	return ring_read_ch(&rx_ring);
+}
+
+void serial_putc(uint8_t data)
+{
+	while (ring_write_ch(&tx_ring, data) < 0)
+		;
+	switch (stat_tx) {
+	case ACTIVE:
+	default:
+		/* Enable the TXE interrupt. */
+		UCSR0B = _BV(RXCIE0) | _BV(RXEN0) | _BV(TXEN0) | _BV(UDRIE0);
+		break;
+	}
+}
+