Implement proper build system

Makefile

@@ -4,34 +4,125 @@
 # Makefile                                                                      
 # Written by Leon Krieg <info@madcow.dev>
 
+# ==============================================================================
+# GENERAL SETTINGS
+# ==============================================================================
+
+SRCDIR    := src
+BINDIR    := bin
+TMPDIR    := $(BINDIR)/build
+TARGET    := $(BINDIR)/core.hex
+ELFFILE   := $(BINDIR)/core.elf
+LOGFILE   := $(BINDIR)/core.log
+
+VERBOSE   := false
 ARCH      := m32
 FREQ      := 8000000UL
 MCU       := atmega32a
 ASP       := usbasp
-GCC       := avr-gcc
+CC        := avr-gcc
+LD        := $(CC)
+OBJCOPY   := avr-objcopy
 AVD       := avrdude
-RMF       := rm -f
-BINDIR    := bin
-ELFILE    := $(BINDIR)/out.elf
-TARGET    := $(BINDIR)/core.hex
-CFLAGS    := -Os -std=c99 -Wall -Wextra -Werror
+MKDIR     := mkdir -p
+RMR       := rm -rf
+
 CPPFLAGS  := -DF_CPU=$(FREQ)
+CFLAGS    := -mmcu=$(MCU) -Os -std=c99 -Wall -Wextra -Werror
+OCFLAGS   := -j .text -j .data -O ihex
+LDFLAGS   := -mmcu=$(MCU)
+LDLIBS    :=
+
+# ==============================================================================
+# TARGET FILE LISTS (DERIVED FROM SOURCE TREE)
+# ==============================================================================
+
+PATHS     := $(shell find "$(SRCDIR)" -type d -printf '%P ' 2>/dev/null)
+FILES     := $(shell find "$(SRCDIR)" -type f -name "*.c"  -printf '%P ' 2>/dev/null)
+TMPDIRS   := $(BINDIR) $(TMPDIR) $(PATHS:%=$(TMPDIR)/%)
+OBJECTS   := $(FILES:%.c=$(TMPDIR)/%.o)
+DEPENDS   := $(FILES:%.c=$(TMPDIR)/%.d)
+
+# ==============================================================================
+# AUXILIARY TARGETS (AND FUSE SETTINGS)
+# ==============================================================================
 
 .PHONY: all
 all: flash
 
 .PHONY: flash
 flash: $(TARGET)
-	$(AVD) -c $(ASP) -p $(ARCH) \
-	       -U lfuse:w:0xff:m    \
-	       -U hfuse:w:0x99:m    \
+	$(E) "[AVD] Flashing..."
+	$(Q) $(AVD) -l $(LOGFILE)    \
+	       -c $(ASP) -p $(ARCH)  \
+	       -U lfuse:w:0xff:m     \
+	       -U hfuse:w:0x99:m     \
 	       -U flash:w:$(TARGET)
 
-$(TARGET): src/main.c
-	$(GCC) -o $(ELFILE) $(CFLAGS) $(CPPFLAGS) $^ -mmcu=$(MCU)
-	avr-objcopy -j .text -j .data -O ihex $(ELFILE) $@
-	avr-size --format=avr --mcu=$(MCU) $@
-
+.PHONY: clean
 clean:
-	$(RMF) $(TARGET)
-	$(RMF) $(ELFILE)
+	$(E) "[REM] $(TARGET)"
+	$(Q) $(RMR) $(TARGET)
+	$(E) "[REM] $(ELFFILE)"
+	$(Q) $(RMR) $(ELFFILE)
+	$(E) "[REM] $(LOGFILE)"
+	$(Q) $(RMR) $(LOGFILE)
+	$(E) "[REM] $(TMPDIR)"
+	$(Q) $(RMR) $(TMPDIR)
+
+.PHONY: distclean
+distclean: clean
+	$(E) "[REM] $(BINDIR)"
+	$(Q) $(RMR) $(BINDIR)
+
+$(TMPDIRS):
+	$(E) "[DIR] $@"
+	$(Q) $(MKDIR) $@
+
+# ==============================================================================
+# PRIMARY BUILD TARGET AND PATTERN RULES
+# ==============================================================================
+
+# We must expand the prerequisite lists a second time to resolve path variable
+# $(@D). This means folders can be set as explicit dependencies and created in
+# the $TMPDIRS rule. This is better than relying on Make to honor the order of
+# prerequisites for the primary target and we will not have to call mkdir for
+# each build step preemptively.
+
+.SECONDEXPANSION:
+
+$(TARGET): $(ELFFILE) | $$(@D)
+	$(E) "[HEX] $@"
+	$(Q) $(OBJCOPY) $(OCFLAGS) $< $@
+
+$(ELFFILE): $(OBJECTS) $(DEPENDS) | $$(@D)
+	$(E) "[ELF] $@"
+	$(Q) $(LD) -o $@ $(LDFLAGS) $(OBJECTS) $(LDLIBS)
+
+$(TMPDIR)/%.o: $(SRCDIR)/%.c | $$(@D)
+	$(E) "[OBJ] $@"
+	$(Q) $(CC) -c -o $@ $(CFLAGS) $(CPPFLAGS) $<
+
+$(TMPDIR)/%.d: $(SRCDIR)/%.c | $$(@D)
+	$(E) "[DEP] $@"
+	$(Q) $(CC) -c -o $@ $(CFLAGS) $(CPPFLAGS) -MM -MT $(@:.d=.o) $<
+
+# ==============================================================================
+# MAKE PREPROCESSOR INCLUDES AND CONDITIONALS
+# ==============================================================================
+
+# Load header dependency rules
+include $(wildcard $(DEPENDS))
+
+# Sanity check
+ifeq ($(strip $(OBJECTS)),)
+$(error No sources found in '$(SRCDIR)/')
+endif
+
+# Handle verbosity setting
+ifneq ($(VERBOSE), false)
+E = @true
+else
+E = @echo
+Q = @
+endif