Non-working makefile (compiles, but code does not run on microcontroller)

Makefile

PRG					    = binaryclock
MCU_TARGET	            = atmega328p
PROGRAMMER	            = usbtiny
PFLAGS			        = #-P /dev/ttyUSB0
OPTIMIZE		        = -Os

DEFS				    = -DF_CPU=1000000UL
LIBS				    =
HEADERS			        =

CC					    = avr-gcc
override CFLAGS			= -g -Wall $(OPTIMIZE) -mmcu=$(MCU_TARGET) $(DEFS)
override LDFLAGS		= -W1,-Map,$(PRG).map

OBJCOPY			        = avr-objcopy
OBJDUMP			        = avr-objdump

FLASH				    = avrdude

all: $(PRG).hex

$(PRG).hex: $(PRG).elf
	$(OBJCOPY) -O ihex -R .eeprom $(PRG).elf $(PRG).hex

$(PRG).elf: $(PRG).o twimaster.o
	$(CC) $(PRG).o twimaster.o -o $(PRG).elf

$(PRG).o: $(PRG).c $(HEADERS)
	$(CC) $(CFLAGS) -c $(PRG).c -o $(PRG).o

twimaster.o: twimaster.c
	$(CC) $(CFLAGS) -c twimaster.c -o twimaster.o

flash:
	$(FLASH) -c $(PROGRAMMER) $(PFLAGS) -p $(MCU_TARGET) -U flash:w:$(PRG).hex