diff --git a/board/Makefile.legacy b/board/Makefile.legacy
index 8d1456f..4d494db 100644
--- a/board/Makefile.legacy
+++ b/board/Makefile.legacy
@@ -1,6 +1,6 @@
 # :set noet
 PROJ_NAME = comma
-CFLAGS  = -g -O0 -Wall
+CFLAGS  = -g -O0 -Wall -std=gnu90
 
 CFLAGS += -mlittle-endian -mthumb -mcpu=cortex-m3
 CFLAGS += -msoft-float -DSTM32F2 -DSTM32F205xx
diff --git a/board/__init__.py b/board/__init__.py
deleted file mode 100644
index e69de29..0000000
diff --git a/board/build.mk b/board/build.mk
index bc49103..09d6e80 100644
--- a/board/build.mk
+++ b/board/build.mk
@@ -1,3 +1,7 @@
+DEPDIR := obj/.d
+$(shell mkdir -p $(DEPDIR) >/dev/null)
+DEPFLAGS = -MT $@ -MMD -MP -MF $(DEPDIR)/$*.Td
+
 CFLAGS += -I inc -I ../ -nostdlib -fno-builtin
 CFLAGS += -Tstm32_flash.ld
 
@@ -67,23 +71,23 @@ obj/cert.h: ../crypto/getcertheader.py
 	../crypto/getcertheader.py ../certs/debug.pub ../certs/release.pub > $@
 
 obj/%.$(PROJ_NAME).o: %.c obj/cert.h obj/gitversion.h config.h
-	$(CC) $(CFLAGS) -o $@ -c $<
+	$(CC) $(DEPFLAGS) $(CFLAGS) -o $@ -c $<
 
 obj/%.$(PROJ_NAME).o: ../crypto/%.c
-	$(CC) $(CFLAGS) -o $@ -c $<
+	$(CC) $(DEPFLAGS) $(CFLAGS) -o $@ -c $<
 
 obj/$(STARTUP_FILE).o: $(STARTUP_FILE).s
-	$(CC) $(CFLAGS) -o $@ -c $<
+	$(CC) $(DEPFLAGS) $(CFLAGS) -o $@ -c $<
 
 obj/$(PROJ_NAME).bin: obj/$(STARTUP_FILE).o obj/main.$(PROJ_NAME).o obj/early.$(PROJ_NAME).o obj/llgpio.$(PROJ_NAME).o obj/can.$(PROJ_NAME).o obj/uart.$(PROJ_NAME).o obj/gpio.$(PROJ_NAME).o obj/libc.$(PROJ_NAME).o
   # hack
-	$(CC) -Wl,--section-start,.isr_vector=0x8004000 $(CFLAGS) -o obj/$(PROJ_NAME).elf $^
+	$(CC) $(DEPFLAGS) -Wl,--section-start,.isr_vector=0x8004000 $(CFLAGS) -o obj/$(PROJ_NAME).elf $^
 	$(OBJCOPY) -v -O binary obj/$(PROJ_NAME).elf obj/code.bin
 	SETLEN=1 ../crypto/sign.py obj/code.bin $@ $(CERT)
 
 obj/bootstub.$(PROJ_NAME).bin: obj/$(STARTUP_FILE).o obj/bootstub.$(PROJ_NAME).o obj/sha.$(PROJ_NAME).o obj/rsa.$(PROJ_NAME).o obj/early.$(PROJ_NAME).o obj/llgpio.$(PROJ_NAME).o obj/libc.$(PROJ_NAME).o
-	$(CC) $(CFLAGS) -o obj/bootstub.$(PROJ_NAME).elf $^
+	$(CC) $(DEPFLAGS) $(CFLAGS) -o obj/bootstub.$(PROJ_NAME).elf $^
 	$(OBJCOPY) -v -O binary obj/bootstub.$(PROJ_NAME).elf $@
 
 clean:
-	rm -f obj/*
+	rm -fr obj
diff --git a/board/obj/.placeholder b/board/obj/.placeholder
deleted file mode 100644
index e69de29..0000000