Store setup settings in eeprom

To have the values of `value_contrast` and `value_backlight` persist
over turn offs they are loaded and stored from and in the eeprom.

For preventing the flash target from earasing the eeprom the `EESAVE`
high fuse byte is set to 0 (programmed).

The values are now loaded when booted and stored when a new value is
set in the setup menu.

firmware/src/Makefile

@@ -5,9 +5,12 @@ PROGRAMMER := usbasp
 SPEED := 8000000UL
 
 TARGET := main.hex
+EEP := main.eep
 BIN := main.elf
 OBJ := main.o
 
+HIGH_FUSE := 0xD6
+
 SHELL := sh
 CC := avr-gcc
 OBJCOPY := avr-objcopy
@@ -16,24 +19,33 @@ AVRDUDE := avrdude
 
 CFLAGS := -mmcu=$(MCU) -D F_CPU=$(SPEED) -Os -Wall -Werror -Wextra
 
-all: $(TARGET)
+all: $(TARGET) $(EEP)
 
 $(TARGET): $(BIN)
 	${OBJCOPY} -O ihex -j .text -j .data $< $@
 
+$(EEP): $(BIN)
+	${OBJCOPY} --change-section-lma .eeprom=0 -O ihex -j .eeprom $< $@
+
 $(BIN): $(OBJ)
 	$(CC) $(CFLAGS) $< -o $@
 
 %.o: %.c
 	$(CC) $(CFLAGS) -c $< -o $@
 
-.PHONY: flash clean check size
+.PHONY: flash eeprom fuses clean check size
 
 flash: $(TARGET) size
 	$(AVRDUDE) -p $(MCU) -c $(PROGRAMMER) -U flash:w:$<:a
 
+eeprom: $(EEP) size
+	$(AVRDUDE) -p $(MCU) -c $(PROGRAMMER) -U eeprom:w:$<:a
+
+fuses:
+	$(AVRDUDE) -p $(MCU) -c $(PROGRAMMER) -U hfuse:w:$(HIGH_FUSE):m
+
 clean:
-	$(RM) $(TARGET) $(BIN) $(OBJ)
+	$(RM) $(TARGET) $(EEP) $(BIN) $(OBJ)
 
 check:
 	cppcheck main.c

firmware/src/main.c

@@ -1,3 +1,4 @@
+#include <avr/eeprom.h>
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
@@ -15,6 +16,9 @@
 #define ENC_A (PINB & (1 << PB6))
 #define ENC_B (PINB & (1 << PB7))
 
+uint8_t EEMEM eeprom_contrast = 0;
+uint8_t EEMEM eeprom_backlight = 0;
+
 static const uint8_t sacred_chao[200] = { 0x00, 0x00, 0x00, 0x00, 0x80, 0xC0, 0xE0, 0xF0, 0xF0, 0xF8, 0xFC, 0xFC, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFE, 0xFE, 0xFC, 0xFC, 0xF8, 0xF0, 0xF0, 0xE0, 0xC0, 0x80, 0x00, 0x00, 0x00, 0x00,
                                           0x80, 0xF0, 0xFC, 0xFE, 0xFF, 0xFF, 0x7F, 0x3F, 0x1F, 0x3F, 0x3F, 0x7F, 0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x7F, 0x1F, 0x0F, 0x0F, 0x07, 0x07, 0x07, 0x03, 0xC3, 0xE3, 0x73, 0x37, 0x17, 0x07, 0x0F, 0x1E, 0x3C, 0xF0, 0x80,
                                           0xFF, 0xFF, 0xFF, 0xE7, 0xC3, 0x81, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0x0F, 0x00, 0x00, 0xFC, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFC, 0x30, 0x00, 0x00, 0xFF,
@@ -553,10 +557,12 @@ static void update_setup(enum input event) {
             change_state(home);
             break;
         case change_contrast:
+            eeprom_update_byte(&eeprom_contrast, value_contrast);
             setup_state = contrast;
             lcd_setup();
             break;
         case change_backlight:
+            eeprom_update_byte(&eeprom_backlight, value_backlight);
             setup_state = backlight;
             lcd_setup();
             break;
@@ -571,10 +577,12 @@ static void update_setup(enum input event) {
             break;
         case change_contrast:
             setup_state = contrast;
+            value_contrast = eeprom_read_byte(&eeprom_contrast);
             lcd_setup();
             break;
         case change_backlight:
             setup_state = backlight;
+            value_backlight = eeprom_read_byte(&eeprom_backlight);
             lcd_setup();
             break;
         }
@@ -676,6 +684,10 @@ ISR(TIMER1_COMPA_vect) {
 }
 
 int main(void) {
+    // Load contrast and backlight values from EEPROM
+    value_contrast = eeprom_read_byte(&eeprom_contrast);
+    value_backlight = eeprom_read_byte(&eeprom_backlight);
+
     // FastPWM: 1.25kHz
     // TODO: Try to get the backlit even more dim
     TCCR0A = (1 << WGM01) | (1 << WGM00) | (1 << COM0B1);