Add CONFIG parameter on make

Makefile

@@ -4,6 +4,14 @@ DEFAULT_CONFIG_LOCATION = 454656
 CONFIG_LOCATION = 458752
 HTML_LOCATION = 262144
 
+# Startup configuration embedded in the image. Override it to build a specific
+# machine with its own configuration: make MACHINE=<name> CONFIG=<file>
+CONFIG ?= config.txt
+
+# Startup configuration embedded in the image. Override it to build a specific
+# machine with its own configuration: make MACHINE=<name> CONFIG=<file>
+CONFIG ?= config.txt
+
 SDCC_PREFIX = toolchain/sdcc-$(shell cat sdcc/* | cksum | cut -d' ' -f1)
 ifeq ($(origin CC),default)
 SDCC = $(SDCC_PREFIX)/bin/sdcc
@@ -46,6 +54,7 @@ ifndef BUILDDIR
 	BUILDDIR = output/$(MACHINE)
 endif
 
+CONFIG_STAMP := $(BUILDDIR)/.config
 VERSION_HEADER := version.h
 
 GIT_VERSION := $(shell git rev-parse --short HEAD)
@@ -68,9 +77,10 @@ BUILD_DATE := $(shell date -u -d @$(SOURCE_DATE_EPOCH) +"%Y-%m-%d %H:%M:%S" 2>/d
 	|| date -u -r $(SOURCE_DATE_EPOCH) +"%Y-%m-%d %H:%M:%S")
 endif
 
-# $(MACHINE_SRC) is listed here so an unknown $MACHINE fails before anything else
-# is built, including the tools/ subdirectory.
-all: create_build_dir $(VERSION_HEADER) $(MACHINE_SRC) $(SUBDIRS) $(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin
+# $(MACHINE_SRC) and $(CONFIG) are listed here so an unknown $MACHINE or a
+# missing config file fails before anything else is built, including the tools/
+# subdirectory.
+all: create_build_dir $(VERSION_HEADER) $(MACHINE_SRC) $(CONFIG) $(SUBDIRS) $(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin
 
 bank_size:
 	tools/bank_occupancy.sh "$(MACHINE)"
@@ -91,6 +101,12 @@ $(MACHINE_SRC):
 	@echo "       Example: make MACHINE=KP_9000_6XHML_X2" >&2
 	@false
 
+# Fail with a clear message when CONFIG names a file that does not exist.
+$(CONFIG):
+	@echo "ERROR: CONFIG='$(CONFIG)' does not exist." >&2
+	@echo "       Point CONFIG at a configuration file, or omit it to use config.txt." >&2
+	@false
+
 # Keep the per-machine definition in first position to fail immediately on an
 # invalid $MACHINE value
 SRCS = \
@@ -209,6 +225,12 @@ FORCE:
 $(CCFLAGS_STAMP): FORCE | create_build_dir
 	@echo '$(CC_FLAGS)' | cmp -s - $@ 2>/dev/null || echo '$(CC_FLAGS)' > $@
 
+# The same for $(CONFIG): its path is stamped so switching to a config file
+# older than the image still rebuilds it, while $(CONFIG) itself as a normal
+# prerequisite covers edits to the selected file.
+$(CONFIG_STAMP): FORCE | create_build_dir
+	@echo '$(CONFIG)' | cmp -s - $@ 2>/dev/null || echo '$(CONFIG)' > $@
+
 $(BUILDDIR)/%.rel: %.c $(CCFLAGS_STAMP) | create_build_dir html_data.h
 	$(CC) -MMD $(CC_FLAGS) -o $@ -c $<
 
@@ -222,11 +244,11 @@ $(BUILDDIR)/rtlplayground.ihx: $(OBJS) $(BUILDDIR)/crtbank.rel $(BUILDDIR)/crc16
 $(BUILDDIR)/rtlplayground.img: $(BUILDDIR)/rtlplayground.ihx
 	objcopy --input-target=ihex -O binary $< $@
 
-$(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin: $(BUILDDIR)/rtlplayground.img | tools
+$(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin: $(BUILDDIR)/rtlplayground.img $(CONFIG) $(CONFIG_STAMP) | tools
 	if [ -e $@ ]; then rm $@; fi
-	tools/$(BUILDDIR)/imagebuilder -i $^ $@
-	tools/$(BUILDDIR)/fileadder -a $(DEFAULT_CONFIG_LOCATION) -s $(IMAGESIZE) -d config.txt $@
-	tools/$(BUILDDIR)/fileadder -a $(CONFIG_LOCATION) -s $(IMAGESIZE) -d config.txt $@
+	tools/$(BUILDDIR)/imagebuilder -i $(BUILDDIR)/rtlplayground.img $@
+	tools/$(BUILDDIR)/fileadder -a $(DEFAULT_CONFIG_LOCATION) -s $(IMAGESIZE) -d "$(CONFIG)" $@
+	tools/$(BUILDDIR)/fileadder -a $(CONFIG_LOCATION) -s $(IMAGESIZE) -d "$(CONFIG)" $@
 	tools/$(BUILDDIR)/fileadder -a $(HTML_LOCATION) -s $(IMAGESIZE) -z -d $(HTML_MIN) -b BANK1 $@
 	tools/$(BUILDDIR)/crc_calculator -u $@
 	ln -sf $(MACHINE)/rtlplayground-$(FILENAME_EXTENSION).bin $(BUILDDIR)/../rtlplayground.bin