add support for external TWI ADC

Makefile

@@ -1,7 +1,7 @@
 MCU = atmega8
 F_CPU = 8000000
 TARGET = funkenschlag
-SRC = funkenschlag.c serial.c src_adc.c src_sw.c src_ds.c datenschlag.c
+SRC = funkenschlag.c serial.c twi.c src_adc.c src_sw.c src_ds.c src_twi_adc.c datenschlag.c
 COMBINE_SRC = 0
 
 include avr-tmpl.mk

config.h

@@ -1,10 +1,16 @@
 /*** Funkenschlag configuration file ***/
 
+// use TWI?
+//#define ENABLE_TWI
+
 /* ADC configuration */
 
-// enable ADC4 and ADC5 - this disables I²C!
+// enable ADC4 and ADC5 - cannot be used in conjunction with TWI/I²c!
 //#define USE_ADC4_ADC5
 
+// enable PCF 8159 ADC via TWI
+//#define USE_TWI_ADC
+
 /* Datenschlag configuration */
 
 #define DS_RETRANSMITS 0

funkenschlag.c

@@ -8,9 +8,11 @@
 #include <util/delay.h>
 #include "config.h"
 #include "serial.h"
+#include "twi.h"
 #include "src_adc.h"
 #include "src_sw.h"
 #include "src_ds.h"
+#include "src_twi_adc.h"
 #include "datenschlag.h"
 #include "datenschlag_structs.h"
 
@@ -36,6 +38,7 @@
 #define SRC_ADC 1
 #define SRC_SW  2
 #define SRC_DS  3
+#define SRC_TWI_ADC  4
 #define SRC_ID(s,n) ( (((s)&0x0F)<<4) | ((n)&0x0F) )
 
 #define SRC_SYS(n)  ((n)>>4)
@@ -51,6 +54,9 @@ static uint8_t channel_source[] = {
 #ifdef USE_ADC4_ADC5
 	SRC_ID(SRC_ADC, 4),
 	SRC_ID(SRC_ADC, 5),
+#elif defined(USE_TWI_ADC)
+	SRC_ID(SRC_TWI_ADC, 0),
+	SRC_ID(SRC_TWI_ADC, 1),
 #endif
 };
 
@@ -84,6 +90,9 @@ static int16_t get_channel(uint8_t i) {
 		case SRC_DS:
 			val = ds_get_next_pulse();
 			break;
+		case SRC_TWI_ADC:
+			val = twi_adc_get(SRC_NUM(src));
+			break;
 		default: /* unknown source */
 			break;
 	}
@@ -125,13 +134,20 @@ int main(void) {
 	VOL_PORT |= (1<<VOL_BIT); // enable pullup
 
 	serial_init();
+#ifdef ENABLE_TWI
+	twi_init();
+#endif
 
 	/* configure switches */
 	sw_init();
 
 	/* configure ADC */
 	adc_init();
 
+#if defined(USE_TWI_ADC)
+	twi_adc_init();
+#endif
+
 	/* configure watchfog timer to reset after 60ms */
 	wdt_enable(WDTO_60MS);
 
@@ -187,6 +203,11 @@ int main(void) {
 		/* prepare Datenschlag data frames */
 		ds_prepare();
 
+#ifdef USE_TWI_ADC
+		/* query TWI/I²C ADC */
+		twi_adc_query();
+#endif
+
 		/* check voltage */
 		if ((~VOL_PIN) & 1<<VOL_BIT) {
 			// everything OK

src_twi_adc.c

@@ -0,0 +1,48 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/wdt.h>
+#include <util/delay.h>
+#include "config.h"
+#include "serial.h"
+#include "src_twi_adc.h"
+#include "twi.h"
+
+/* PCF8591 I²C ADC/DAC */
+#define TWI_ADC_ADDR 0x48
+#define TWI_ADC_CHANNELS 4
+
+uint16_t twi_adc_raw   [TWI_ADC_CHANNELS] = {0};
+int16_t  twi_adc_values[TWI_ADC_CHANNELS] = {0};
+
+static int16_t read_adc(uint8_t adc) {
+	uint8_t result = 0;
+	twi_start(TWI_ADC_ADDR<<1);
+	twi_write(adc);
+	twi_stop();
+	twi_start((TWI_ADC_ADDR<<1) | 1);
+	twi_read(1); /* discard first response */
+	result = twi_read(0);
+	return result;
+}
+
+int16_t twi_adc_get(uint8_t n) {
+	return twi_adc_values[n];
+}
+
+uint16_t twi_adc_get_raw(uint8_t n) {
+	return twi_adc_raw[n];
+}
+
+void twi_adc_query(void) {
+	/* keep sampling adc data */
+	for (uint8_t adc = 0; adc < TWI_ADC_CHANNELS; adc++) {
+		/* scale to 10 bit values */
+		twi_adc_raw[adc] = read_adc(adc);
+		twi_adc_values[adc] = twi_adc_raw[adc]<<2;
+	}
+}
+
+void twi_adc_init(void) {
+}

src_twi_adc.h

@@ -0,0 +1,4 @@
+void twi_adc_init(void);
+void twi_adc_query(void);
+int16_t twi_adc_get(uint8_t n);
+uint16_t twi_adc_get_raw(uint8_t n);

twi.c

@@ -0,0 +1,44 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <avr/io.h>
+#include <avr/pgmspace.h>
+#include <avr/interrupt.h>
+#include <util/twi.h>
+#include "twi.h"
+
+void twi_init(void) {
+	TWSR = 0;
+	TWBR = (F_CPU / 100000UL - 16) / 2;
+	TWCR = 1<<TWEN;
+}
+
+static void twi_wait(void) {
+	while (!(TWCR & (1<<TWINT)));
+}
+
+void twi_start(uint8_t addr) {
+	TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
+	twi_wait();
+	TWDR = addr;
+	TWCR = (1<<TWINT) | (1<<TWEN);
+	twi_wait();
+}
+
+void twi_stop(void) {
+	TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
+}
+
+void twi_write(uint8_t data) {
+	TWDR = data;
+	TWCR = (1<<TWINT) | (1<<TWEN);
+	twi_wait();
+}
+
+uint8_t twi_read(uint8_t ack) {
+	TWCR = (1<<TWINT) | (1<<TWEN) | (ack? (1<<TWEA) : 0);
+	twi_wait();
+	uint8_t result = TWDR;
+	if (!ack) twi_stop();
+	return result;
+}

twi.h

@@ -0,0 +1,5 @@
+void twi_init(void);
+void twi_start(uint8_t addr);
+void twi_stop(void);
+uint8_t twi_read(uint8_t ack);
+void twi_write(uint8_t data);