AVR USART file not recognized in C - c

Question

I have the following test setup below. When I compile the code, I get the following error: The initUSART is not recognized, but I have included the file in the appropriate places. Did I miss out on anything?
AVR Development Stack
Get input main.c file...
Compile code and return elf file...
main.o: In function `main':
/Users/sebastianscharf/Documents/Hardware/AVR/main.c:14: undefined reference to `initUSART'
collect2: error: ld returned 1 exit status
avr-objcopy: 'main.elf': No such file
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.00s
avrdude: Device signature = 0x1e950f (probably m328p)
avrdude: Expected signature for ATmega328 is 1E 95 14
Double check chip, or use -F to override this check.
avrdude done. Thank you.
main file
#include "config.h"
#include <avr/io.h>
#include <util/delay.h>
#include "USART.h"
int main(void) {
char serialCharacter;
// --- INITS --- //
DDRB = 0xff;
// Set up LED for output
initUSART();
return 0;
}
USART.h
/* These are defined for convenience */
#define USART_HAS_DATA bit_is_set(UCSR0A, RXC0)
#define USART_READY bit_is_set(UCSR0A, UDRE0)
uint8_t receiveByte(void);
/* Takes the defined BAUD and F_CPU, calculates the bit-clock multiplier, and configures the hardware USART*/
void initUSART(void);
USART.c
#include "config.h"
#include <avr/io.h>
#include <util/setbaud.h>
#include "USART.h"
void initUSART(void) {
// Requires BAUD
UBRR0H = UBRRH_VALUE;
UBRR0L = UBRRL_VALUE;
#if USE_2X
UCSR0A |= (1 << U2X0);
#else
UCSR0A &= ~(1 << U2X0);
#endif
// Enable USART
UCSR0B = (1 << TXEN0) | (1 << RXEN0);
UCSR0C = (1 << UCSZ01) | (1 << UCSZ00); // 8 data bits, 1 stop bit
}
bash file
#!/bin/bash
source bashColors.sh
echo -e "${IGreen}AVR Development Stack${Reset}"
echo -e "${BIBlue}Get input main.c file...${Reset}"
avr-gcc -g -Os -mmcu=atmega328p -c main.c USART.c &&
echo -e "${BIBlue}Compile code and return elf file...${Reset}"
avr-gcc -g -mmcu=atmega328p -o main.elf main.o &&
echo -e "${BIBlue}Convert elf file to hex...${Reset}"
# avr-objcopy converts into hex file. -j indicates that we want the information from the .text and .data segment extracted.
avr-objcopy -j .text -j .data -O ihex main.elf out.hex &&
echo -e "${BIBlue}Uploading data to microcontroller...${Reset}"
avrdude -c usbtiny -p m328

Answer 1

You compiled both source files properly to .o with:
avr-gcc -g -Os -mmcu=atmega328p -c main.c USART.c
Now the main.o file contains an external reference to initUSART (partly thanks to the #include "USART.h" directive which provides the proper prototype)
but this link line:
avr-gcc -g -mmcu=atmega328p -o main.elf main.o &&
only references main.o. You need to add USART.o so the symbol is resolved by the linker (the linker doesn't care about .h include files), like this:
avr-gcc -g -mmcu=atmega328p -o main.elf main.o USART.o &&