AVR demo

In this project I test low-level functionality of an AVR-microcontroller (atmega328p). Everything is written from scratch in C and Assembly. Functionality includes:

• Toggle LED
• Busy wait
• Sleep
• Measure time
• Print over USART

Setup

Software

Install the packages: avr-gcc, avr-binutils, avr-libc, avrdude

Hardware

• ATMEGA328P (No Arduino bootloader needed)
• Breadboard (or something else to attach things too)
• LED
• Resistors
• Wires
• AVR programmer (I'm using AVR Pocket programmer, others should work too).

Programmer

Connect the programmer. Note that the AVR Pocket programmer has a built-in 5V supply. Other programmers might need to connect that separately.

Programmer	AVR
MOSI	17 (MOSI)
MISO	18 (MISO)
RST	1 (RESET)
SCK	19 (SCK)
5V	7 & 20
GND	8

LED

Connect the LED in series with a resistor from pin 23 (PC0) to ground.

Read prints

The printf function is implemented to use USART as out-stream. However to read the print it needs to be connected to a separate computer with some wiring.

Raspberry Pi

The TX (3) pin on atmega328p should be connected to the RX (10) pin on the Raspberry Pi. However the voltage needs to be dropped from 5 V to 3.3 V. That can be done with a simple voltage slitter using 2 resistors.

                RX (3.3 V)
                 |
GND ---/\/\/\/---|---/\/\/\/--- TX (5 V)
        2 kΩ          1 kΩ

Also connect the two grounds.

Then from the Raspberry Pi using the program minicom the prints can be read with the command:

minicom -b 9600 -o -D /dev/serial0

Raspberry Pi Pico UART-USB bridge + Linux computer

Download Pico UART-USB bridge software (uf2 file).

Hold the BOOTSEL button on the Raspberry Pi Pico and insert the USB cable.

Create a mount-point:

sudo mkdir -p /mnt/pico

Find the device name (x in /dev/sdx)

dmsg | tail

mount:

sudo mount /dev/sdx1 /mnt/pico

copy uf2 file, unmount:

sudo cp pico-uart-bridge-v3.0.uf2 /mnt/pico
sudo sync
sudo umount /mnt/pico

Now connect the device.

The TX (3) pin on atmega328p should be connected to the RX (10) pin on the Raspberry Pi Pico. However the voltage needs to be dropped from 5 V to 3.3 V. That can be done with a simple voltage slitter using 2 resistors.

                RX (3.3 V)
                 |
GND ---/\/\/\/---|---/\/\/\/--- TX (5 V)
        2 kΩ          1 kΩ

Also connect the two grounds.

Then open the terminal with:

sudo picocom /dev/ttyACM0 -b 9600 -l

Installation and programming (Linux)

Install avrdude, avr-libc, avr-gcc and avr-binutils.

Clone this repository.

Verify good connections:

make verify

Set fuses (internal clock 8 MHz):

make fuse

This only has to be done once.

Build program and flash to processor:

make flash

Debugging (gdb simulation)

Install avr-gdb and simavr.

Replace -Os with -Og in Makefile COMPILE variable.

make

Start simavr

simavr -m atmega328p -f 1000000 main.elf -g

Connect with gdb

avr-gdb
file main.elf
target remote :1234
load