avr-gcc undefined reference to function in linked object file - c

Question

I have some code for handling all uart related functions and operations in a .h/.c pair that I usually include in my project. I have a makefile that compiles all of my .c files into .o files then links them all to one executable. For some reason, one of my projects using this pair compiles fine but the other gives this error:
obj/fiveax.o: In function `fiveax_init':
fiveax.c:(.text+0x10): undefined reference to `uart_init'
collect2: error: ld returned 1 exit status
when trying to link to the exectutable after compiling all the .o files. I have included my makefile below, it is the same for both projects with the only difference being the appname.
Makefile
########################################################################
####################### Makefile Template ##############################
########################################################################
# Compiler settings - Can be customized.
CC = avr-gcc
CXXFLAGS = -mmcu=atmega2560 -D BUILD=1
LDFLAGS = -Iinclude -Ilibs/FreeRTOS/include -Llibs/FreeRTOS -lfreertos
DEV = /dev/ttyUSB0
AVRCONF = -C/etc/avrdude.conf
AVRLOAD = $(AVRCONF) -v -patmega2560 -carduino -P$(DEV) -b57600 -D -Uflash:w:bin/$(APPNAME).hex:i
# Makefile settings - Can be customized.
APPNAME = FiveAx
EXT = .c
SRCDIR = src
OBJDIR = obj
INCDIR = include
DEPDIR = dep
############## Do not change anything from here downwards! #############
SRC = $(wildcard $(SRCDIR)/*$(EXT))
OBJ = $(SRC:$(SRCDIR)/%$(EXT)=$(OBJDIR)/%.o)
DEP = $(OBJ:$(OBJDIR)/%.o=$(DEPDIR)/%.d)
# UNIX-based OS variables & settings
RM = rm
DELOBJ = $(OBJ)
# Windows OS variables & settings
DEL = del
EXE = .exe
WDELOBJ = $(SRC:$(SRCDIR)/%$(EXT)=$(OBJDIR)\\%.o)
########################################################################
####################### Targets beginning here #########################
########################################################################
all: bin $(APPNAME)
# Builds the app
$(APPNAME): $(OBJ)
$(CC) $(CXXFLAGS) -o bin/$#.elf $^ $(LDFLAGS)
avr-objcopy -j .text -j .data -O ihex bin/$(APPNAME).elf bin/$(APPNAME).hex
bin:
mkdir -p $#
# Creates the dependecy rules
$(DEPDIR)/%.d: $(SRCDIR)/%$(EXT)
#$(CPP) $(CFLAGS) $< -MM -MT $(#:$(DEPDIR)/%.d=$(OBJDIR)/%.o) >$# $(LDFLAGS)
# Includes all .h files
-include $(DEP)
# Building rule for .o files and its .c/.cpp in combination with all .h
$(OBJDIR)/%.o: $(SRCDIR)/%$(EXT)
$(CC) $(CXXFLAGS) -o $# -c $< $(LDFLAGS)
load: bin $(APPNAME)
avrdude $(AVRLOAD)
################### Cleaning rules for Unix-based OS ###################
# Cleans complete project
.PHONY: clean
clean:
$(RM) -r $(DELOBJ) $(DEP) bin
# Cleans only all files with the extension .d
.PHONY: cleandep
cleandep:
$(RM) $(DEP)
edit: I have included the header file for uart.h in the source file.
edit: I was asked for the output of the makefile
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o obj/uart.o -c src/uart.c -Llibs/FreeRTOS -lfreertos
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o obj/servo.o -c src/servo.c -Llibs/FreeRTOS -lfreertos
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o obj/main.o -c src/main.c -Llibs/FreeRTOS -lfreertos
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o obj/fiveax.o -c src/fiveax.c -Llibs/FreeRTOS -lfreertos
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o bin/FiveAx.elf obj/uart.o obj/servo.o obj/main.o obj/fiveax.o
obj/fiveax.o: In function `fiveax_init':
fiveax.c:(.text+0x10): undefined reference to `uart_init'
collect2: error: ld returned 1 exit status
make: *** [Makefile:41: FiveAx] Error 1

Answer 1

It's impossible to read the information requested because it's not formatted as a code block so all the lines run together. Please use the live preview feature of the SO question editor to check that the content you're adding is readable, to save the sanity of the people trying to help you.
The link line appears to be this:
avr-gcc -mmcu=atmega2560 -D BUILD=1 -Iinclude -Ilibs/FreeRTOS/include -o bin/FiveAx.elf obj/uart.o obj/servo.o obj/main.o obj/fiveax.o
Here we can see that the library -lfreertos is not present, and also that all the object files come at the end after the flags. I don't see how this could have happened given the makefile you show above:
CXXFLAGS = -mmcu=atmega2560 -D BUILD=1
LDFLAGS = -Iinclude -Ilibs/FreeRTOS/include -Llibs/FreeRTOS -lfreertos
$(CC) $(CXXFLAGS) -o bin/$#.elf $^ $(LDFLAGS)
so it seems that the make output here doesn't match the makefile you've shown us. Are you sure you're using that makefile?