diff --git a/.gitignore b/.gitignore
index 0157077..2c4bf08 100644
--- a/.gitignore
+++ b/.gitignore
@@ -256,3 +256,4 @@ cython_debug/
 # PyPI configuration file
 .pypirc
 
+pyupdi-env/
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..a45ecdc
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,37 @@
+cmake_minimum_required(VERSION 3.13)
+
+# Project
+project(lezyne-rear-light-firmware C)
+
+# MCU and clock
+set(MCU attiny202)
+set(F_CPU 5000000UL) # 5 MHz
+
+# Toolchain executables
+set(CMAKE_SYSTEM_NAME Generic)
+set(CMAKE_C_COMPILER avr-gcc)
+set(OBJCOPY avr-objcopy)
+
+# Compiler flags
+set(CMAKE_C_FLAGS "-mmcu=${MCU} -DF_CPU=${F_CPU} -Os -Wall")
+
+# Sources
+add_executable(main.elf main.c)
+
+# HEX file
+add_custom_command(
+    OUTPUT main.hex
+    COMMAND ${OBJCOPY} -O ihex -R .eeprom main.elf main.hex
+    DEPENDS main.elf
+)
+
+# BIN file
+add_custom_command(
+    OUTPUT main.bin
+    COMMAND ${OBJCOPY} -O binary -R .eeprom main.elf main.bin
+    DEPENDS main.elf
+)
+
+# Targets
+add_custom_target(hex ALL DEPENDS main.hex)
+add_custom_target(bin ALL DEPENDS main.bin)
diff --git a/README.md b/README.md
index 747ff62..ece524c 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,86 @@
 # lezyne-rear-light-firmware
 
-Open firmware for Lezyne bike rear lights based on ATTINY202
\ No newline at end of file
+Open firmware for Lezyne bike rear lights based on ATTINY202
+
+This repository contains a minimal firmware as a **C project** for the ATtiny202 microcontroller using **GCC**, **CMake**, and **VS Code**. It also includes instructions for programming the chip using an **FT232 USB-UART adapter** via the UPDI interface with `pymcuprog`.  
+
+---
+
+## Table of Contents
+
+- [Dependencies](#dependencies)
+- [Setup Build Environment](#setup-build-environment)
+- [Building the Project](#building-the-project)
+- [Flashing the Firmware](#flashing-the-firmware)
+- [Reading Flash Content](#reading-flash-content)
+- [Hardware Setup](#hardware-setup)
+- [License](#license)
+
+---
+
+## Dependencies
+
+Ensure the following tools are installed on your system:
+
+- **GCC AVR toolchain** (supports ATtiny 0/1-series)  
+  ```bash
+  sudo zypper install avr-gcc avr-libc
+    ```
+- **CMake**
+  ```bash
+    sudo zypper install cmake
+    ```
+- **Python 3, pip and venv**
+  ```bash
+    sudo zypper install python3 python3-pip python3-venv
+    ```
+- **VS Code** (optional but recommended)
+- **CMake Tools extension** for VS Code
+
+## Setup Build Environment
+1. Clone the repository:
+   ```bash
+    git clone https://git.mosad.xyz/localhorst/lezyne-rear-light-firmware
+    cd lezyne-rear-light-firmware
+    ```
+2. Configure the CMake project:
+    - Open the folder in VS Code.
+    - Select the AVR-GCC kit in the bottom blue bar.
+    - Run CMake: Configure (from command palette) if it doesn't auto-run.
+
+## Building the Project
+1. Press F7 or Ctrl+Shift+B to build.
+2. Output files are generated in the 'build/' folder:
+- main.elf → ELF executable
+- main.hex → HEX file (flashable)
+- main.bin → BIN file
+
+## Flashing the Firmware
+Hardware: FT232 USB-UART adapter connected to UPDI with a 4.7 kΩ resistor.
+1. Create and activate a Python virtual environment:
+   ```bash
+    python3 -m venv pyupdi-env
+    source pyupdi-env/bin/activate
+    ```
+2. Install pymcuprog inside the environment:
+   ```bash
+    pip install pymcuprog
+   ```
+3. Verify installation:
+   ```bash
+    pymcuprog --version
+   ```
+4. Flash using pymcuprog:
+   ```bash
+    pymcuprog -t uart -u /dev/ttyUSB0 -d attiny202 write -f build/main.hex
+   ```
+## Hardware Setup (FT232 → ATtiny202 UPDI)
+   ```bash
+    FT232 TX ----[4.7kΩ]---- UPDI (pin 6)
+    FT232 GND --------------- GND
+    VCC -------------------- VCC (3.3V or 5V, must match FT232 logic)
+   ```
+
+## License
+
+This project is licensed under the MIT License. See [LICENSE](./LICENSE) for details.
\ No newline at end of file
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..2fc3bc1
--- /dev/null
+++ b/main.c
@@ -0,0 +1,14 @@
+#define F_CPU 5000000UL // 5 MHz
+#include <avr/io.h>
+#include <util/delay.h>
+
+int main(void) {
+    // Configure PA3 as output (Pin 7 on ATTINY202-SSN)
+    VPORTA.DIR |= (1 << 3);
+    
+
+    while (1) {
+        VPORTA.OUT ^= (1 << 3);  // toggle PA3
+        _delay_ms(500);
+    }
+}