From 27321e05de35b494c2b282652e1c40a18435b68b Mon Sep 17 00:00:00 2001
From: Jonas Gunz <himself@jonasgunz.de>
Date: Fri, 4 Jun 2021 19:09:07 +0200
Subject: implement uart

---
 Makefile   | 19 +++++++++++++---
 src/main.c | 40 ++++++++++++++++++++++++++++++++-
 src/uart.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/uart.h | 36 ++++++++++++++++++++++++++++++
 4 files changed, 166 insertions(+), 4 deletions(-)
 create mode 100644 src/uart.c
 create mode 100644 src/uart.h

diff --git a/Makefile b/Makefile
index 38f5292..386814d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,18 @@
 MCU             = atmega8
-CPUFREQ         = 160000000
 PROGRAMMER      = dragon_isp
 
+CPUFREQ         = 8000000 #8MHz
+BAUD            = 9600
+
+# https://www.engbedded.com/fusecalc/
+# Int. RC Osc. 8MHz
+# No WD
+# No BOD
+LFUSE           = 0xc4
+HFUSE           = 0xd9
+
 CC              = avr-gcc
-CFLAGS          = -std=c89 -Wall -mmcu=$(MCU) -DF_CPU=$(CPUFREQ)
+CFLAGS          = -std=c89 -Wall -mmcu=$(MCU) -DF_CPU=$(CPUFREQ) -DBAUD=$(BAUD)
 LDFLAGS         = -mmcu=$(MCU)
 BUILDDIR        = build
 SOURCEDIR       = src
@@ -19,6 +28,7 @@ build: dir $(OBJ)
 	@echo LD $(OBJ)
 	@$(CC) $(CFLAGS) -o $(BUILDDIR)/$(OUTPUT) $(OBJ) $(LDFLAGS)
 	@avr-objcopy -O ihex $(BUILDDIR)/$(OUTPUT) $(BUILDDIR)/$(OUTPUT).hex
+	@avr-size --mcu=$(MCU) --format=avr $(BUILDDIR)/$(OUTPUT)
 
 debug: -D _DEBUG
 debug: build;
@@ -41,7 +51,10 @@ clean:
 all: clean build
 
 flash: build
-	@avrdude -p $(MCU) -c $(PROGRAMMER) -U flash:w:$(BUILDDIR)/$(OUTPUT).hex:i
+	@sudo avrdude -p $(MCU) -c $(PROGRAMMER) -U flash:w:$(BUILDDIR)/$(OUTPUT).hex:i
+
+fuse:
+	@sudo avrdude -p $(MCU) -c $(PROGRAMMER) -U lfuse:w:$(LFUSE):m -U hfuse:w:$(HFUSE):m
 
 devsetup:
 	@echo "--target=avr -isystem /usr/avr/include/ $(CFLAGS)" | tr ' ' '\n' > compile_flags.txt
diff --git a/src/main.c b/src/main.c
index c0f35d7..a73e7ef 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2,24 +2,62 @@
 #include <avr/interrupt.h>
 #include <stdint.h>
 
+#include "uart.h"
+
+uint8_t t0_ovf_cnt = 0;
+
+uint8_t pb0_thresh = 128;
+
 ISR(TIMER0_OVF_vect) {
 	cli();
+	/*TCNT0 = (1<<7);*/ /* Hack-increase Interrupt trigger freq */
+
+	t0_ovf_cnt ++;
+
+	if ( t0_ovf_cnt >= pb0_thresh )
+		PORTB &= ~(1<<PINB0);
+	else
+		PORTB |= (1<<PINB0);
 
 	sei();
 }
 
+ISR(TIMER2_OVF_vect) {
+	cli();
+	pb0_thresh ++;
+	sei();
+}
+
 int main(void) {
+	char c;
+
 	cli();
 
-	/* Enable TIMER0 with interrupt */
+	/* Pins */
+	DDRB |= (1<<PINB0);
+
+	/* Enable TIMER0 with interrupt, no prescaler */
 	TCCR0 |= (1<<CS00);
 	TIMSK |= (1<<TOIE0);
+
+	/* Enable TIMER2 with interrupt, Clk divide by 1024 */
+	/*
+	TCCR2 |= (7<<CS20);
+	TIMSK |= (1<<TOIE2);
+	*/
+
+	/* Uart */
+	uart_init();
 	
 	/* Go! */
 	sei();
 
 	while(1){
+		if( uart_getchar(&c) )
+			continue;
 
+		uart_putchar(c);
+		pb0_thresh = c;
 	}
 
 	return 0;
diff --git a/src/uart.c b/src/uart.c
new file mode 100644
index 0000000..0b65e30
--- /dev/null
+++ b/src/uart.c
@@ -0,0 +1,75 @@
+/*
+ * src/uart.c
+ * (c) 2021 Jonas Gunz <himself@jonasgunz.de>
+ * License: All rights reserved.
+ */
+
+#include "uart.h"
+
+struct ringbuff_s {
+	uint8_t buffer[256];
+	uint8_t read;
+	uint8_t write;
+} rxc_buf, txc_buf ;
+
+ISR(USART_RXC_vect) {
+	cli();
+
+	/* Discard if buffer full */
+	if( rxc_buf.read - 1 == rxc_buf.write )
+		goto end;
+
+	rxc_buf.buffer[rxc_buf.write] = UDR;
+	rxc_buf.write++;
+
+end:
+	sei();
+}
+
+ISR(USART_UDRE_vect) {
+	cli();
+
+	/* Prevent interrupt loops */
+	if( txc_buf.read == txc_buf.write ) {
+		UCSRB &= ~(1<<UDRIE);
+		goto end;
+	}
+
+	UDR = txc_buf.buffer[txc_buf.read];
+	txc_buf.read++;
+
+end:
+	sei();
+}
+
+void uart_init(){
+	memset( &txc_buf, 0, sizeof(txc_buf) );
+	memset( &rxc_buf, 0, sizeof(rxc_buf) );
+
+	UBRRH = (uint8_t)((UBRR)>>8);
+	UBRRL = (uint8_t)(UBRR);
+
+	UCSRB |= (1<<RXEN)|(1<<RXCIE)|(1<<TXEN);
+}
+
+uint8_t uart_putchar(char _c) {
+	if( txc_buf.read - 1 == txc_buf.write )
+		return 1;
+
+	txc_buf.buffer[txc_buf.write] = _c;
+	txc_buf.write ++;
+
+	UCSRB |= (1<<UDRIE);
+
+	return 0;
+}
+
+uint8_t uart_getchar(char *_c) {
+	if( rxc_buf.read == rxc_buf.write )
+		return 1;
+
+	*_c = rxc_buf.buffer[rxc_buf.read];
+	rxc_buf.read++;
+
+	return 0;
+}
diff --git a/src/uart.h b/src/uart.h
new file mode 100644
index 0000000..c709487
--- /dev/null
+++ b/src/uart.h
@@ -0,0 +1,36 @@
+/*
+ * src/uart.h
+ * (c) 2021 Jonas Gunz <himself@jonasgunz.de>
+ * License: All rights reserved.
+ */
+
+/*
+ * Interrupt controlled UART
+ */
+
+#ifndef _UART_H_
+#define _UART_H_
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+#include <string.h>
+
+#ifndef BAUD
+#warning BAUD "BAUD not defined. Dafaulting to 9600"
+#define BAUD 9600
+#endif
+
+#ifndef F_CPU
+#error "F_CPU not defined"
+#endif
+
+#define UBRR F_CPU/16/BAUD-1
+
+void uart_init();
+
+uint8_t uart_putchar(char _c);
+
+uint8_t uart_getchar(char *_c);
+
+#endif
-- 
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