From 0065fb630fada99649bb167fc454872a699ae4e3 Mon Sep 17 00:00:00 2001
From: finga <finga@onders.org>
Date: Thu, 18 Feb 2021 22:00:24 +0100
Subject: [PATCH] Generate a PWM signal for the display

Generate a variable duty cycle PWM signal for the dimmable display
backlight at a frequency of 1.25kHz.

For demo und testing purposes PD5 is currently fading between 0 and
100%.
---
 .gitignore            |  3 +++
 firmware/src/Makefile | 41 +++++++++++++++++++++++++++++++++++++++++
 firmware/src/main.c   | 31 +++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 firmware/src/Makefile
 create mode 100644 firmware/src/main.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a39790f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*.o
+*.elf
+*.hex
diff --git a/firmware/src/Makefile b/firmware/src/Makefile
new file mode 100644
index 0000000..e546649
--- /dev/null
+++ b/firmware/src/Makefile
@@ -0,0 +1,41 @@
+.SUFFIXES:
+
+MCU := atmega328p
+PROGRAMMER := usbtiny
+
+TARGET := main.hex
+BIN := main.elf
+OBJ := main.o
+
+SHELL := sh
+CC := avr-gcc
+OBJCOPY := avr-objcopy
+SIZE := avr-size
+AVRDUDE := avrdude
+
+CFLAGS := -mmcu=$(MCU) -Os -Wall -Werror -Wextra -Wpedantic
+
+all: $(TARGET)
+
+$(TARGET): $(BIN)
+	${OBJCOPY} -O ihex -j .text -j .data $< $@
+
+$(BIN): $(OBJ)
+	$(CC) $(CFLAGS) $< -o $@
+
+%.o: %.c
+	$(CC) $(CFLAGS) -Os -c $< -o $@
+
+.PHONY: flash clean check size
+
+flash: $(TARGET) size
+	$(AVRDUDE) -p $(MCU) -c $(PROGRAMMER) -U flash:w:$<:a
+
+clean:
+	$(RM) main.o main.elf main.hex
+
+check:
+	cppcheck main.c
+
+size: $(BIN)
+	$(SIZE) --format=avr --mcu=$(MCU) $<
diff --git a/firmware/src/main.c b/firmware/src/main.c
new file mode 100644
index 0000000..fc9b488
--- /dev/null
+++ b/firmware/src/main.c
@@ -0,0 +1,31 @@
+#define	F_CPU   8000000UL
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <stdbool.h>
+
+int main(void) {
+    // FastPWM: 1.25kHz
+    TCCR0A = (1 << WGM01) | (1 << WGM00) | (1 << COM0B1);
+    TCCR0B = (1 << CS01) | (1 << WGM02); // prescaler = 8;
+    OCR0A = 100;
+    OCR0B = 10;
+    DDRD |= (1 << PD5);
+
+    bool reverse = 0;
+
+    while (1) {
+        _delay_ms(1);
+
+        if (OCR0B > 100)
+            reverse = !reverse;
+
+        if (reverse)
+            OCR0B++;
+        else
+            if (OCR0B > 0)
+                OCR0B--;
+            else
+                reverse = !reverse;
+    }
+}