commit ac04dfc73fbc13076131230cf01dfe6c432cb47c
Author: Daniel Knüttel <daniel.knuettel@daknuett.eu>
Date:   Tue Jan 1 16:48:54 2019 +0100

    initial

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f2ff63b
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,15 @@
+CC=avr-gcc
+CFLAG= -mmcu=atmega8 -O
+
+objects= time.o usart.o main.o ringbuffer.o
+
+all:main.elf
+
+%.o:%.c
+	$(CC) $(CFLAG) -c -o $@ $<
+
+
+main.elf: $(objects)
+	$(CC) $(objects) $(CFLAG) -o main.elf
+install: main.elf
+	avrdude -p m168 -c avrispmkii  -U flash:w:main.elf:a
diff --git a/conf.h b/conf.h
new file mode 100644
index 0000000..d833817
--- /dev/null
+++ b/conf.h
@@ -0,0 +1,8 @@
+#ifndef _CONF_H_
+#define _CONF_H_
+
+#define F_CPU 8000000UL
+#define USART_BAUD 9600
+#define USART_BUFFER_SIZE 256
+
+#endif
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..78b510b
--- /dev/null
+++ b/main.c
@@ -0,0 +1,19 @@
+#include "time.h"
+#include "usart.h"
+#include <util/delay.h>
+
+int main(void)
+{
+	time_init();
+	usart_init();
+
+	while(1)
+	{
+		_delay_ms(1000);
+		unsigned int eigentime = get_eigentime();
+		usart_putc((char) eigentime);
+		usart_putc((char)(eigentime >> 8));
+	}
+	return 0;
+}
+
diff --git a/ringbuffer.c b/ringbuffer.c
new file mode 100644
index 0000000..7f373f4
--- /dev/null
+++ b/ringbuffer.c
@@ -0,0 +1,59 @@
+#include "ringbuffer.h"
+#include <stdlib.h>
+
+ringbuffer_t
+ringbuffer_new(size_t size)
+{
+	ringbuffer_t buffer = malloc(sizeof(struct ringbuffer_s));
+	if(!buffer)
+	{
+		return NULL;
+	}
+
+	buffer->buffer = malloc(sizeof(char) * size);
+	if(!buffer->buffer)
+	{
+		free(buffer);
+		return NULL;
+	}
+
+	buffer->length = size;
+	buffer->head = 0;
+	buffer->tail = 0;
+	buffer->ovf = 0;
+	return buffer;
+}
+
+int 
+ringbuffer_nonempty(ringbuffer_t buffer)
+{
+	return buffer->head != buffer->tail;
+}
+
+unsigned char
+ringbuffer_get_char(ringbuffer_t buffer)
+{
+	unsigned char result;
+	if(buffer->head == buffer->tail)
+	{
+		return 0;
+	}
+	result = buffer->buffer[buffer->tail];
+	buffer->tail = (buffer->tail + 1) % buffer->length;
+	return result;
+}
+
+int
+ringbuffer_put_char(ringbuffer_t buffer
+		, unsigned char c)
+{
+	buffer->ovf = 0;
+	buffer->buffer[buffer->head] = c;
+	buffer->head = (buffer->head + 1) % buffer->length;
+	if(buffer->head == buffer->tail)
+	{
+		buffer->ovf = 1;
+	}
+	return buffer->ovf;
+}
+
diff --git a/ringbuffer.h b/ringbuffer.h
new file mode 100644
index 0000000..c1fa67d
--- /dev/null
+++ b/ringbuffer.h
@@ -0,0 +1,23 @@
+#ifndef _RINGBUFFER_H_
+#define _RINGBUFFER_H_
+
+#include <stdlib.h>
+
+typedef struct ringbuffer_s
+{
+	size_t length;
+	size_t head, tail;
+	unsigned char * buffer;
+	char ovf;
+} * ringbuffer_t;
+
+ringbuffer_t
+ringbuffer_new(size_t size);
+int 
+ringbuffer_nonempty(ringbuffer_t buffer);
+unsigned char
+ringbuffer_get_char(ringbuffer_t buffer);
+int
+ringbuffer_put_char(ringbuffer_t buffer
+		, unsigned char c);
+#endif
diff --git a/time.c b/time.c
new file mode 100644
index 0000000..f9a4295
--- /dev/null
+++ b/time.c
@@ -0,0 +1,28 @@
+#include "time.h"
+#include "conf.h"
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+
+volatile unsigned int _eigentime_ms;
+
+void
+time_init(void)
+{
+	_eigentime_ms = 0;
+	TCCR1B = _BV(CS10);
+	OCR1A = TIMER1_COMPA_VALUE;
+	TIMSK |= _BV(OCIE1A);
+}
+
+
+unsigned int 
+get_eigentime(void)
+{
+	return _eigentime_ms;
+}
+
+ISR(TIMER1_COMPA_vect)
+{
+	_eigentime_ms++;
+}
diff --git a/time.h b/time.h
new file mode 100644
index 0000000..9f465c2
--- /dev/null
+++ b/time.h
@@ -0,0 +1,16 @@
+#ifndef _TIME_H_
+#define _TIME_H_
+#include "conf.h"
+
+#define TIMER1_MAX_VALUE 0xffff
+#define TIMER1_COMPA_VALUE (TIMER1_MAX_VALUE / F_CPU)
+
+extern volatile unsigned int _eigentime_ms;
+
+unsigned int 
+get_eigentime(void);
+
+void
+time_init(void);
+
+#endif
diff --git a/usart.c b/usart.c
new file mode 100644
index 0000000..c0f0687
--- /dev/null
+++ b/usart.c
@@ -0,0 +1,35 @@
+#include <avr/io.h>
+#include <stdlib.h>
+#include "usart.h"
+#include "conf.h"
+#include "ringbuffer.h"
+
+volatile ringbuffer_t usart_buffer;
+
+
+void
+usart_init(void)
+{
+	usart_buffer = ringbuffer_new(USART_BUFFER_SIZE);
+	UBRRH = (unsigned char)(UBRR_VALUE >> 8);
+	UBRRL = (unsigned char)UBRR_VALUE;
+	UCSRB = _BV(TXEN) | _BV(TXCIE);
+	UCSRC = _BV(USBS) | _BV(UCSZ0) | _BV(UCSZ1);
+}
+
+int
+usart_putc(char c)
+{
+	return ringbuffer_put_char(usart_buffer, c);
+}
+	
+
+
+ISR(USART_TX_vect)
+{
+	if(ringbuffer_nonempty(usart_buffer))
+	{
+		while(!(UCSRA & UDRE));
+		UDR = ringbuffer_get_char(usart_buffer);
+	}
+}
diff --git a/usart.h b/usart.h
new file mode 100644
index 0000000..be7099d
--- /dev/null
+++ b/usart.h
@@ -0,0 +1,14 @@
+#ifndef _USART_H_
+#define _USART_H_
+
+#include "conf.h"
+#define UBRR_VALUE (F_CPU/16/USART_BAUD-1)
+
+void
+usart_init(void);
+
+
+int
+usart_putc(char c);
+
+#endif