I'm currently trying to read values from a temperature sensor (Dallas ds18b20) with an AVR atmega328p. In order to read values, I need to import an external library (using this one). I have used the Makefile in the external repository to create a static library (libds18b20.a
in lib
directory). I also added the header files to my own source. I have the following Makefile:
PORT_ID=/dev/ttyACM0
MCU=atmega328p
F_CPU=1200000
CC=avr-gcc
PROGRAMMER_ID=stk500v1
OBJCOPY=avr-objcopy
CFLAGS=-std=c99 -Wall -g -Os -mmcu=${MCU} -DF_CPU=${F_CPU} -I.
TARGET=main
SRCS=main.c
BAUD_RATE=19200
PATH_DS18B20=./lib
all:
${CC} -L ${PATH_DS18B20} ${CFLAGS} -o ${TARGET}.bin ${SRCS}
${OBJCOPY} -j .text -j .data -O ihex ${TARGET}.bin ${TARGET}.hex
flash:
avrdude -v -P ${PORT_ID} -b ${BAUD_RATE} -c ${PROGRAMMER_ID} -p ${MCU} -U flash:w:${TARGET}.hex
clean:
rm -f *.bin *.hex
However, when I try to run this Makefile I got the following errors (output partially omitted):
/main.c:(.text.startup+0x2e): undefined reference to `ds18b20convert'
/main.c:60: undefined reference to `ds18b20read'
These functions are defined in the headers files. I'm expecting that the static library is not properly linked. What am I doing wrong here?
I managed to get this working by omitting the -L
flag and put the path directly behind the ${SRCS}
-variable including the name of the static library:
PORT_ID=/dev/ttyACM0
MCU=atmega328p
F_CPU=1200000
CC=avr-gcc
PROGRAMMER_ID=stk500v1
OBJCOPY=avr-objcopy
CFLAGS=-std=c99 -Wall -g -Os -mmcu=${MCU} -DF_CPU=${F_CPU} -I.
TARGET=main
SRCS=main.c
BAUD_RATE=19200
PATH_DS18B20=./lib/libds18b20.a
all:
${CC} ${CFLAGS} -o ${TARGET}.bin ${SRCS} ${PATH_DS18B20}
${OBJCOPY} -j .text -j .data -O ihex ${TARGET}.bin ${TARGET}.hex
flash:
avrdude -v -P ${PORT_ID} -b ${BAUD_RATE} -c ${PROGRAMMER_ID} -p ${MCU} -U flash:w:${TARGET}.hex
clean:
rm -f *.bin *.hex