# HG changeset patch
# User John Tsiombikas <nuclear@member.fsf.org>
# Date 1359359535 -7200
# Node ID 40b150fedb0ef0969abe30d317c4e21f929f92bd
# Parent  d26d73ef2db7394fda0904d5dd40c6cca0cd6bb3
foo

diff -r d26d73ef2db7 -r 40b150fedb0e voltmeter.c
--- a/voltmeter.c	Sun Jan 27 10:11:40 2013 +0200
+++ b/voltmeter.c	Mon Jan 28 09:52:15 2013 +0200
@@ -3,6 +3,7 @@
 
 #include <stdio.h>
 #include <avr/io.h>
+#include <avr/interrupt.h>
 #include <util/delay.h>
 
 /* hardware setup
@@ -12,6 +13,7 @@
  *     bit 1: R/W
  *     bit 2: E
  */
+#define LCD_BUS_WIDTH	8
 
 #define BIT_RS	3
 #define BIT_RW	4
@@ -57,10 +59,23 @@
 
 FILE stream_lcd = FDEV_SETUP_STREAM(lcd_stream_write, NULL, _FDEV_SETUP_WRITE);
 
+int bn_pressed;
+unsigned char foo;
+
 int main(void)
 {
 	stdout = stderr = &stream_lcd;
 
+	/* port B[0] out -> backlight
+	 * port B[1] in <- backlight switch
+	 */
+	DDRB = 1;
+	PORTB = 0xfe;	/* enable all pullups, leave bit0 -> 0 (backlight) */
+	/* enable PIN B1 interrupt */
+	PCMSK0 = 2;
+	PCICR = 1;
+	sei();	/* enable interrupts */
+
 	DDRC = 0xfe;
 	PORTC = 0;	/* disable pullups */
 
@@ -74,18 +89,36 @@
 		long val = read_adc();
 		double ref = 1.08 * 1.47 / 0.47;
 		double voltage = ref * (double)val / (double)1024;
+
 		lcd_clear();
 
 		if(val == 1023) {
-			printf("*** RANGE ***   ");
+			printf("*** RANGE ***");
 		} else {
-			printf("%.2f volts      ", voltage);
+			printf("%.2f volts", voltage);
+		}
+
+		/* check if the backlight button was pressed */
+		if(bn_pressed & 1) {
+			if(PORTB & 1) {
+				PORTB &= 0xfe;
+			} else {
+				PORTB |= 1;
+			}
+			bn_pressed = 0;
 		}
 		_delay_ms(500);
 	}
 	return 0;
 }
 
+
+ISR(PCINT0_vect) {
+	if((PINB & 2) == 0) {
+		bn_pressed = 1;
+	}
+}
+
 void setup_adc(void)
 {
 	/* disable digital input buffer on ADC0 pin */
@@ -114,10 +147,39 @@
 	return low | ((long)ADCH << 8);
 }
 
+void lcd_write_byte(unsigned char byte)
+{
+#if LCD_BUS_WIDTH == 8
+	DDRD = 0xff;
+	PORTD = byte;
+#else
+	DDRD = (DDRD & 0xf0) | 0xf;
+
+	PORTD = (PORTD & 0xf0) | ((byte >> 4) & 0xf);
+	PORTD = (PORTD & 0xf0) | (byte & 0xf);
+#endif
+}
+
+unsigned char lcd_read_byte(void)
+{
+#if LCD_BUS_WIDTH == 8
+	DDRD = 0;
+	PORTD = 0;	/* disable pull-ups */
+
+	return PIND;
+#else
+	unsigned char byte;
+
+	DDRD = DDRD & 0xf0;
+	PORTD &= 0xf0;	/* disable pull-ups */
+
+	byte = (PIND & 0xf) << 4;
+	return byte | (PIND & 0xf);
+#endif
+}
+
 void lcd_init(void)
 {
-	DDRD = 0x0f;	/* port d[0, 3] -> output */
-
 	/* make sure the display has time to boot up */
 	_delay_ms(20);
 
@@ -125,55 +187,53 @@
 
 	clear_bit(BIT_E);
 	clear_bit(BIT_RS);
-	PORTD = CMD_FUNC | FUNC_BUS_8BIT | FUNC_LINES_2 | FUNC_FONT_5x8;
+#if LCD_BUS_WIDTH == 8
+	lcd_write_byte(CMD_FUNC | FUNC_BUS_8BIT | FUNC_LINES_2 | FUNC_FONT_5x8);
+#else
+	lcd_write_byte(CMD_FUNC | FUNC_BUS_4BIT | FUNC_LINES_2 | FUNC_FONT_5x8);
+#endif
 	enable();
 	lcd_wait_busy();
 
 	clear_bit(BIT_RS);
-	PORTD = CMD_ONOFF | ONOFF_DISP | ONOFF_CURSOR;
+	lcd_write_byte(CMD_ONOFF | ONOFF_DISP);
 	enable();
 	lcd_wait_busy();
 
 	clear_bit(BIT_RS);
-	PORTD = CMD_ENTRY_MODE | (1 << 1);
+	lcd_write_byte(CMD_ENTRY_MODE | (1 << 1));
 	enable();
 	lcd_wait_busy();
 }
 
 void lcd_clear(void)
 {
-	DDRD = 0xff;	/* port d -> output */
-
 	clear_bit(BIT_RW);
 
 	clear_bit(BIT_E);
 	clear_bit(BIT_RS);
-	PORTD = CMD_CLEAR;
+	lcd_write_byte(CMD_CLEAR);
 	enable();
 	lcd_wait_busy();
 }
 
 void lcd_set_cursor_addr(unsigned int addr)
 {
-	DDRD = 0xff;	/* port d -> output */
-
 	clear_bit(BIT_RW);
 
 	clear_bit(BIT_E);
 	clear_bit(BIT_RS);
-	PORTD = CMD_DDRAM_ADDR | addr;
+	lcd_write_byte(CMD_DDRAM_ADDR | addr);
 	enable();
 	lcd_wait_busy();
 }
 
 void lcd_putchar(char c)
 {
-	DDRD = 0xff;	/* port d -> output */
-
 	clear_bit(BIT_RW);
 
 	set_bit(BIT_RS);
-	PORTD = c;
+	lcd_write_byte(c);
 	enable();
 	lcd_wait_busy();
 }
@@ -196,9 +256,6 @@
 {
 	unsigned char data;
 
-	DDRD = 0;		/* port d -> input */
-	PORTD = 0;		/* disable pull-ups */
-
 	do {
 		NSDELAY();
 		clear_bit(BIT_E);
@@ -209,13 +266,11 @@
 		NSDELAY();
 		set_bit(BIT_E);
 		NSDELAY();
-		data = PIND;
+		data = lcd_read_byte();
 		clear_bit(BIT_E);
 		clear_bit(BIT_RW);
 
 	} while(data & (1 << 7));
-
-	DDRD = 0xff;	/* port d -> output */
 }
 
 static void enable(void)