ECE 422: Lab 3

#include <avr/io.h>  // Register names
#include <util/delay_basic.h>  // for _delay_loop_2()

/*** Configuration constants ***/
#define LED_PIN PB3

int main(void)
{
    // <avr/sfr_defs.h> defines the macro _BV() as
    //      #define _BV(bit) (1 << (bit))
    // Use PB3 as the output
    DDRB |= _BV(LED_PIN);

    while (1) {
        // toggle pin and do it again
        PORTB ^= _BV(LED_PIN);

        // 65536 iterations, 4 clocks each + call overhead
        _delay_loop_2(0);
    }
}

# minimal Makefile
# no variables or other features except for command line continuations
.PHONY: default
default: main.hex main.lst


main.o: main.c
	avr-gcc -c -mmcu=attiny85 -std=gnu99 -g -Os -flto -Wall -Wextra \
	    -DF_CPU=8000000 main.c

main.elf: main.o
	avr-gcc -mmcu=attiny85 -g -Os -flto -Wall -Wextra \
	    -fuse-linker-plugin -Wl,--gc-sections -o main.elf main.o

main.hex: main.elf
	avr-objcopy -O ihex -R .eeprom main.elf main.hex

main.lst: main.elf
	avr-objdump --disassemble --source --line-numbers --demangle \
	    main.elf > main.lst

.PHONY: clean
clean:
	rm main.o main.elf main.hex main.lst

MCU=attiny85

# Compiler options (for C language)
COMPILE_C_OPTS=
COMPILE_C_OPTS+=-c
COMPILE_C_OPTS+=-mmcu=$(MCU)
COMPILE_C_OPTS+=-std=gnu11
COMPILE_C_OPTS+=-g
COMPILE_C_OPTS+=-Os
COMPILE_C_OPTS+=-flto
COMPILE_C_OPTS+=-Wall -Wextra
COMPILE_C_OPTS+=-DF_CPU=8000000	  # *** must match the fuse settings!

# Linker options
LINK_OPTS=
LINK_OPTS+=-mmcu=$(MCU)
LINK_OPTS+=-g
LINK_OPTS+=-Os
LINK_OPTS+=-flto
LINK_OPTS+=-Wall -Wextra
LINK_OPTS+=-fuse-linker-plugin
LINK_OPTS+=-Wl,--gc-sections

# HEX output options
HEX_OPTS=
HEX_OPTS+=-O ihex
HEX_OPTS+=-R .eeprom

# Listing output options
LST_OPTS=
LST_OPTS+=--disassemble
LST_OPTS+=--source
LST_OPTS+=--line-numbers
LST_OPTS+=--demangle


# The first target is the default if no target was specified.
.PHONY: default
default: main.hex main.lst


# How to compile the .c and get the .o object file.
main.o: main.c
	avr-gcc $(COMPILE_C_OPTS) main.c

# Link the objects together to make a single ELF binary
# There may be more than one for some projects.
main.elf: main.o
	avr-gcc $(LINK_OPTS) -o main.elf main.o

# Generate HEX file for programming the chip
main.hex: main.elf
	avr-objcopy $(HEX_OPTS) main.elf main.hex

# Dump the listing file so we can inspect the generated assembly.
# No line continuations just because.
main.lst: main.elf
	avr-objdump $(LST_OPTS) main.elf > main.lst


.PHONY: clean
clean:
	@-rm main.o main.elf main.hex main.lst