New version, works with external pull-up.

Makefile

@@ -0,0 +1,87 @@
+CC=avr-gcc
+LD=avr-ld
+MCU_TARGET=attiny2313a
+DUDE_TARGET=attiny2313
+AVRDUDE=avrdude
+PORT=/dev/ttyUSB0
+override CFLAGS=-Wall -g -Os -mmcu=${MCU_TARGET}
+override LDFLAGS=
+
+%.o: %.c
+	${CC} ${CFLAGS} -c $<
+
+%.elf: %.o
+	${LD} ${LDFLAGS} -Map $@.map -o $@ $< /usr/lib/avr/lib/libc.a /usr/lib/avr/lib/avr25/crttn2313a.o
+
+%.lst: %.elf
+	avr-objdump -h -S $< > $@
+
+%.lst: %.o
+	avr-objdump -h -S $< > $@
+
+%.hex: %.elf
+	avr-objcopy -j .text -j .data -O ihex $< $@
+
+program-%: %.hex
+	# Write code out
+	${AVRDUDE} -p ${DUDE_TARGET} -P ${PORT} -U flash:w:$<
+
+clean:
+	rm -f *.o *.elf *.elf.map *.lst *.hex
+
+# Project-specific
+install: program-paul_1
+
+erase:
+	${AVRDUDE} -p ${DUDE_TARGET} -P ${PORT} -e
+
+show-fuses:
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0  -U lfuse:r:/dev/stdout:h
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0  -U hfuse:r:/dev/stdout:h
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0  -U efuse:r:/dev/stdout:h
+
+set-fuse:
+	# Nothing to do here.
+
+clear-fuse:
+	# Note: bit=1 means "unprogrammed", bit=0 means "programmed"
+
+	# This is the default: internal 8MHz clock divided by 8 = 1MHz clock
+	#                                                         Divide clock by 8
+	#                                                         |Output clock on CKOUT
+	#                                                         ||SUT1
+	#                                                         |||SUT0
+	#                                                         ||||CKSEL3
+	#                                                         |||||CKSEL2
+	#                                                         ||||||CKSEL1
+	#                                                         |||||||CKSEL0
+	#                                                         ||||||||
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -U lfuse:w:0b01100100:m
+
+	#                                                         DebugWire
+	#                                                         |EESAVE
+	#                                                         ||SPIEN
+	#                                                         |||WDTON
+	#                                                         ||||BODLEVEL2
+	#                                                         |||||BODLEVEL1
+	#                                                         ||||||BODLEVEL0
+	#                                                         |||||||RSTDISBL
+	#                                                         ||||||||
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -U hfuse:w:0b11011111:m
+	# Default: BOD disabled
+
+	#                                                                SELFPRGEN
+	#                                                                |
+	${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -U efuse:w:0b11111111:m
+	# Self Programming: disabled
+
+high-speed:
+	echo sck 8.68 | ${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -t
+
+slow-speed:
+	echo sck 276.7 | ${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -t -F
+
+voltage:
+	echo vtarg 3.0 | ${AVRDUDE} -p ${DUDE_TARGET} -P /dev/ttyUSB0 -t -F
+
+all: slow-speed clear-fuse high-speed install set-fuse