adc improvements

Makefile

@@ -49,7 +49,7 @@ CFLAGS += -ffunction-sections -fdata-sections -Os
 LDFLAGS = -Wl,--gc-sections -Wl,--relax -lm
 
 #LD_FLAGS += -Wl,-u,vfprintf -lprintf_flt -lm  ## for floating-point printf
-#LD_FLAGS += -Wl,-u,vfprintf -lprintf_min      ## for smaller printf
+LD_FLAGS += -Wl,-u,vfprintf -lprintf_min      ## for smaller printf
 
 #############################################
 

lib/adc.c

@@ -1,5 +1,6 @@
 #include <avr/io.h>
 #include <stdint.h>
+#include <stdbool.h>
 
 #include "calc.h"
 #include "adc.h"
@@ -8,7 +9,7 @@
 void adc_init(enum ADC_Prescaller presc)
 {
 	ADCSRA |= presc;  // 128 prescaler -> 125 kHz
-	ADMUX  |= _BV(REFS0);  // Voltage reference
+	ADMUX |= _BV(REFS0);  // Voltage reference
 	sbi(ADCSRA, ADEN);  // Enable ADC
 }
 
@@ -24,26 +25,53 @@ void adc_enable(void)
 	sbi(ADCSRA, ADEN);
 }
 
-static void adc_convert(uint8_t channel)
+/** Start a new conversion */
+void adc_start_conversion(uint8_t channel)
 {
 	set_low_nibble(ADMUX, channel);  // Select channel to sample
-	sbi(ADMUX, ADLAR);  // Align result to left
+	cbi(ADMUX, ADLAR);  // Align result to right
 	sbi(ADCSRA, ADSC);  // Start conversion
+}
+
+/** Check if ADC is done converting */
+bool adc_ready(void)
+{
+	return bit_is_low(ADCSRA, ADSC);
+}
+
+/** Read the result of last conversion with 8bit precision */
+uint8_t adc_read_8bit()
+{
+	uint8_t low = ADCL;
+	uint8_t high = ADCH;
+	return low >> 2 | high << 6;
+}
 
-	while (bit_is_high(ADCSRA, ADSC)); // Wait for it...
+/** Read the result of last conversion with 10bit precision */
+uint16_t adc_read_10bit()
+{
+	uint8_t low = ADCL;
+	uint8_t high = ADCH;
+	return ((uint16_t) high << 8) | low;
+}
+
+/** Start ADC conversion and wait for the result */
+static void adc_convert(uint8_t channel)
+{
+	adc_start_conversion(channel);
+	while (!adc_ready()); // Wait for it...
 }
 
 /** Sample analog pin with 8-bit precision */
-uint8_t adc_read_byte(uint8_t channel)
+uint8_t adc_convert_8bit(uint8_t channel)
 {
 	adc_convert(channel);
-	return ADCH;  // The upper 8 bits of ADC result
+	return adc_read_8bit();
 }
 
-
 /** Sample analog pin with 10-bit precision */
-uint16_t adc_read_word(uint8_t channel)
+uint16_t adc_convert_10bit(uint8_t channel)
 {
 	adc_convert(channel);
-	return ADCW;  // The whole ADC word (10 bits)
+	return adc_read_10bit();
 }

lib/adc.h

@@ -25,8 +25,20 @@ void adc_disable(void);
 /** Enable (already initialized) ADC */
 void adc_enable(void);
 
-/** Sample analog pin with 8-bit precision */
-uint8_t adc_read_byte(uint8_t channel);
+/** Start a new conversion */
+void adc_start_conversion(uint8_t channel);
 
-/** Sample analog pin with 10-bit precision */
-uint16_t adc_read_word(uint8_t channel);
+/** Check if ADC is done converting */
+bool adc_ready(void);
+
+/** Read the result of last conversion with 8bit precision */
+uint8_t adc_read_8bit(void);
+
+/** Read the result of last conversion with 10bit precision */
+uint16_t adc_read_10bit(void);
+
+/** Sample analog pin with 8-bit precision. Blocking! */
+uint8_t adc_convert_8bit(uint8_t channel);
+
+/** Sample analog pin with 10-bit precision. Blocking! */
+uint16_t adc_convert_10bit(uint8_t channel);

main.c

@@ -2,9 +2,9 @@
 #include <avr/pgmspace.h>    // storing data in program memory
 #include <avr/interrupt.h>   // interrupt vectors
 #include <util/delay.h>      // delay functions
-
 #include <stdint.h>          // C header for int types like uint8_t
 #include <stdbool.h>         // C header for the bool type
+#include <stdio.h>
 
 // Include stuff from the library
 #include "lib/iopins.h"
@@ -14,6 +14,9 @@
 
 #include "pinout.h"
 
+/**
+ * Configure pins
+ */
 void setup_io(void)
 {
 	as_output(PIN_DISP_CP);
@@ -35,35 +38,56 @@ void setup_io(void)
 }
 
 // --- LED display brightness control ---
-#define DISP_BRIGHTNESS OCR2B
+volatile uint8_t disp_brightness;
+#define LIGHT_ADC_CHANNEL 6
+
+/**
+ * PWM for LED display dimming
+ */
 void setup_pwm(void)
 {
-	// PWM for LED display dimming
-	TCCR2A |= (1 << WGM20) | (1 << WGM21) | (1 << COM2B1);
-	TCCR2B |= (1 << CS20);
+	OCR2B = disp_brightness = 0xFF;
+	TCCR2A |= _BV(WGM20) | _BV(WGM21) | _BV(COM2B1);
+	TIMSK2 |= _BV(TOIE2);
+	TCCR2B |= _BV(CS20);
+
+	adc_start_conversion(LIGHT_ADC_CHANNEL);
+}
+
+/** ISR that writes the PWM register - to avoid glitches */
+ISR(TIMER2_OVF_vect)
+{
+	// convert in background
+	if (adc_ready()) {
+		disp_brightness = 255 - adc_read_8bit();
+		adc_start_conversion(LIGHT_ADC_CHANNEL);
+	}
 
-	DISP_BRIGHTNESS = 0x7F;
+	OCR2B = disp_brightness;
 }
 
+/**
+ * Let's gooo
+ */
 void main()
 {
 	usart_init(BAUD_115200);
-	usart_isr_rx_enable(true); // enable RX interrupt handler
+	//usart_isr_rx_enable(true); // enable RX interrupt handler
 
+	adc_init(ADC_PRESC_128);
 	setup_io();
 	setup_pwm();
-	adc_init(ADC_PRESC_128);
 
 	// SPI conf
-	spi_init_master(SPI_LSB_FIRST,
-					CPOL_1, CPHA_0,
-					SPI_DIV_2);
+	// TODO verify the cpha and cpol. those seem to work, but it's a guess
+	spi_init_master(SPI_LSB_FIRST, CPOL_1, CPHA_0, SPI_DIV_2);
 
 	// globally enable interrupts
 	sei();
 
 	uint8_t cnt = 0;
 
+	char buf[100];
 	while (1) {
 		pin_down(PIN_DISP_STR);
 		spi_send(cnt);
@@ -73,15 +97,7 @@ void main()
 
 		_delay_ms(100);
 
-		// Brightness directly proportional to light level
-		DISP_BRIGHTNESS = 255 - adc_read_byte(6);
+		sprintf(buf, "%d\n", disp_brightness);
+		usart_puts(buf);
 	}
 }
-
-// UART receive handler
-ISR(USART_RX_vect)
-{
-	// "ECHO" function:
-	uint8_t b = usart_rx();
-	usart_tx(b); // send back
-}

pinout.h

@@ -30,7 +30,7 @@
 #define PIN_PWR_KEY A4 // Direct input from the power key, used for power-off
 #define PIN_PWR_HOLD A5 // Hold the buck enabled. Set 0 for shutdown
 
-// Ambient light sensor (Vdd -> 10k -> * -> phototransistor -> GND)
+// Ambient light sensor (Vdd -> 10k -> * -> photo transistor -> GND)
 #define PIN_LIGHT_SENSE A6 // ADC exclusive pin
 
 #endif //FIRMWARE_PINOUT_H