If you’re diving into the world of embedded systems, the ATtiny85 is a fantastic place to begin. It’s compact, cost-effective, and gives you full control over hardware using register-level programming. In this post, you’ll learn how to set up your Ubuntu machine, wire up your ATtiny85 with a USBasp programmer, and write your first bare-metal firmware.

🛠️ What You’ll Need

Hardware

• ATtiny85 Microcontroller
• USBasp Programmer
• Breadboard + Jumper Wires
• LED + 330Ω Resistor (optional for testing)
• 5V Power Source (from USBasp or external)

💻 Setting Up Ubuntu for ATtiny85 Development

Open a terminal and run the following:

sudo apt update
sudo apt install avrdude gcc-avr avr-libc make

These tools provide:

• avrdude – for uploading firmware via USBasp
• gcc-avr – the AVR C compiler
• avr-libc – standard C library for AVR
• make – to automate the build process

🔌 Wiring ATtiny85 with USBasp Programmer

Here’s how to connect your USBasp to the ATtiny85:

💡 Why Register-Level Programming?

Register-level programming gives you:

• Fine-grained control of microcontroller peripherals
• Deeper understanding of what’s happening under the hood
• Minimal, efficient code—great for low-memory systems

📝 Example: Blinking an LED on PB3 (Pin 2)

Here’s a simple program that toggles an LED connected to PB3 (Pin 2) every 500ms.

main.c

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

int main(void) {
    DDRB |= (1 << PB3); // Set PB3 as output

    while (1) {
        PORTB ^= (1 << PB3); // Toggle PB3
        _delay_ms(500);      // Delay
    }
}

⚙️ Makefile to Build and Flash

Create a file named Makefile in the same directory as main.c:

MCU=attiny85
F_CPU=1000000UL
CC=avr-gcc
CFLAGS=-mmcu=$(MCU) -DF_CPU=$(F_CPU) -Os
OBJCOPY=avr-objcopy
TARGET=main

all: $(TARGET).hex

$(TARGET).hex: $(TARGET).out
	$(OBJCOPY) -O ihex $< $@

$(TARGET).out: $(TARGET).c
	$(CC) $(CFLAGS) -o $@ $<

flash: $(TARGET).hex
	sudo avrdude -c usbasp -p t85 -U flash:w:$(TARGET).hex

clean:
	rm -f *.out *.hex

🔥 Flash the Program

Once everything is connected and saved, flash your firmware using:

make
make flash

You should see the LED blinking on PB3 (pin 2)!

🧪 Optional: Change Clock Frequency

To run the ATtiny85 at 8 MHz (instead of the default 1 MHz), disable the divide-by-8 fuse:

sudo avrdude -c usbasp -p t85 -U lfuse:w:0xE2:m

⚠️ Be cautious with fuse settings—wrong values can disable programming interfaces.

✅ You’re All Set!

You’ve now set up a complete ATtiny85 development workflow on Ubuntu using USBasp! From here, you can explore:

• Timers and PWM
• External interrupts
• ADC (analog to digital conversion)
• UART (via software or USI)

Stay tuned for upcoming posts diving into these features—all with register-level control!