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Digispark: Getting Started - Blink

Note: This documentation is for programming the Digispark with avr-gcc and Makefiles directly, not with the Arduino IDE.

Now that we've got micronucleus up and running on our Digispark (Micronucleus Getting Started) it's time for the hello world of microcontrollers: the blink program!

Repo: https://github.com/matthew-macgregor/digispark-attiny85-experiments/tree/main/1-blink

Our code looks like so:

#include <avr/io.h>
#include <util/delay.h>

// Digispark LED is on Pin 1 for newer versions
#define LED             PB1
#define DELAY_MS        1000

int main(void) {
	DDRB 	|= 	(1 << LED);	// Set pin to output
	PORTB 	|= 	(1 << LED);	// Set pin to high

	for (;;) {
		PORTB ^= (1 << LED);
		_delay_ms(DELAY_MS);
	}

	return 0;
}

We don't need a circuit diagram or a breadboard for this one because we'll just blink the onboard LED. We can use the Makefile below.

• To build: make
• To flash: make flash

Peeking under the hood, the command to actually load the hex onto the board with micronucleus is incredibly simple:

micronucleus --run main.hex

Note: The Digispark programs a bit differently than other boards. Run the command above, then plug in the board (it will prompt you). A trick I found was to connect a jumper wire to P5 RESET and connect it to ground, and then disconnect it. This seems to trigger programming.

# Depends:
# gcc-avr avr-libc micronucleus

DEVICE  = attiny85
CLOCK   = 16000000	# 16mhz
OBJ	= main.o

# Make sure micronucleus is in PATH or change LOADER
LOADER  = micronucleus
GCC	= avr-gcc -Wall -Os -DF_CPU=$(CLOCK) -mmcu=$(DEVICE)  

.PHONY: clean all

all: main.hex

.c.o:
	$(GCC) -c $< -o $@

flash: all
	$(LOADER) --run main.hex

clean:
	rm -f main.hex main.elf $(OBJ)

main.elf: $(OBJ)
	$(GCC) -o main.elf $(OBJ)

main.hex: main.elf
	rm -f main.hex
	avr-objcopy -j .text -j .data -O ihex main.elf main.hex
	avr-size --format=avr --mcu=$(DEVICE) main.elf