A FreeRTOS-based operating system for the RP2350 microcontroller, featuring a windowed desktop environment with PS/2 keyboard and mouse input, DVI display output via HSTX, SD card filesystem support, and the ability to load and run ELF binaries. Compatible with Murmulator OS 2 applications.
- Windowed desktop environment — overlapping windows with title bars, menus, drag-to-move, and a taskbar with Start menu
- Terminal emulator — multiple concurrent terminal windows, each running its own shell instance
- Built-in shell — command-line interface with built-in commands and the ability to launch ELF apps from SD card
- File manager — graphical file browser with large/small icon and list views, cut/copy/paste, and navigation history
- ELF binary loading — load and execute standalone applications compiled against the MOS2 API
- PS/2 keyboard and mouse — direct PS/2 input with full keyboard mapping and mouse cursor support
- DVI video output — 640×480 display via RP2350's HSTX peripheral (4-bit paletted, 16-color CGA/EGA palette)
- SD card filesystem — FAT32 via SPI with FatFs
- PSRAM support — external QSPI PSRAM for application memory (auto-detected at boot)
- FreeRTOS scheduler — preemptive multitasking with separate tasks for input, compositing, USB, and applications
- Hard fault recovery — crash dump saved to uninitialized SRAM, survives warm resets for post-mortem debugging
- MOS2 compatibility layer — system function table and POSIX/musl stubs for running Murmulator OS 2 applications
FRANK OS targets the FRANK M2 board — an RP2350B-based development board with DVI output, PS/2 ports, SD card slot, and PSRAM.
- MCU: RP2350B (QFN-80, 48 GPIO)
- Flash: 4 MB
- PSRAM: QSPI (optional, auto-detected)
- Video: DVI via HSTX peripheral
- Input: PS/2 keyboard + PS/2 mouse
- Storage: SD card (SPI mode)
- LED: GPIO 25
Note: The M1 board layout is no longer supported. FRANK OS builds exclusively for the M2 GPIO layout.
| Signal | GPIO |
|---|---|
| CLK− | 12 |
| CLK+ | 13 |
| D0− | 14 |
| D0+ | 15 |
| D1− | 16 |
| D1+ | 17 |
| D2− | 18 |
| D2+ | 19 |
| Signal | GPIO |
|---|---|
| CLK | 2 |
| DATA | 3 |
| Signal | GPIO |
|---|---|
| CLK | 0 |
| DATA | 1 |
| Signal | GPIO |
|---|---|
| CLK | 6 |
| CMD/MOSI | 7 |
| DAT0/MISO | 4 |
| DAT3/CS | 5 |
| Package | GPIO |
|---|---|
| RP2350A (QFN-60) | 8 |
| RP2350B (QFN-80) | 47 |
Pin is auto-detected at runtime based on the RP2350 package variant.
| Signal | GPIO |
|---|---|
| PWM0 | 20 |
| PWM1 | 21 |
| Beeper | 22 |
| Shortcut | Action |
|---|---|
| Win+T | Open a new terminal window |
| Win+E | Open file manager |
| Win (alone) | Toggle Start menu |
| Alt+Tab | Cycle focus between windows |
| Alt+Space | Open system menu for focused window |
| Alt+F4 | Close focused window |
- Raspberry Pi Pico 2 (RP2350) or compatible board (FRANK M2 recommended)
- Pico SDK (version 2.0+) installed and configured
- ARM GCC toolchain
- CMake 3.13+
picotool(for flashing)
- Install the Raspberry Pi Pico SDK (version 2.0+)
- Set environment variable:
export PICO_SDK_PATH=/path/to/pico-sdk - Install ARM GCC toolchain (
arm-none-eabi-gcc) - Install CMake 3.13+
# Clone the repository with submodules
git clone --recursive https://github.com/rh1tech/frankos.git
cd frankos
# Or if already cloned, initialize submodules
git submodule update --init --recursive
# Build
./build.shThe build script removes any previous build/ directory, runs CMake, and compiles with make -j4. The output firmware is placed in build/.
The following CMake options can be adjusted in CMakeLists.txt:
| Option | Default | Description |
|---|---|---|
PSRAM_SPEED |
84 |
PSRAM max frequency in MHz (set to empty to disable HW init) |
CPU_CLOCK_MHZ |
252 |
CPU clock speed in MHz |
# Flash using the provided script
./flash.sh
# Or specify a firmware path
./flash.sh path/to/firmware.elfThe flash script uses picotool to load the firmware and reboot the device. Both .elf and .uf2 formats are supported.
MOS2-compatible ELF applications can be built separately:
cd apps
./build_apps.shCompiled apps are placed in apps/compiled/ and can be copied to the SD card for execution from the shell.
- Format an SD card as FAT32
- Copy the contents of the
sdcard/directory to the root of the SD card - Insert the card — it is auto-mounted at boot
- Use the shell or file manager to browse and launch applications
FRANK OS is structured around FreeRTOS tasks running on Core 0 of the RP2350:
| Task | Priority | Description |
|---|---|---|
| USB | Highest | TinyUSB device servicing (CDC serial console) |
| Input | 3 | PS/2 keyboard/mouse polling and event routing |
| Compositor | 2 | Window manager event dispatch and screen compositing |
| Heartbeat | 1 | LED blink (system alive indicator) |
| Shell (per terminal) | — | Command-line interpreter for each terminal window |
Core 1 is dedicated to the DispHSTX DVI output driver.
FRANK OS is licensed under the GNU General Public License v3.0 or later.
Portions derived from Murmulator OS 2 by DnCraptor are used under the same license.
Third-party components retain their original licenses (MIT, BSD-3-Clause, ISC, Apache-2.0) as noted in their respective source files.
Mikhail Matveev <xtreme@rh1.tech>, https://rh1.tech
- Project: murmulator-os2
- Author: DnCraptor (GitHub)
- License: GPL-3.0-or-later
- Description: The original MOS2 operating system for Murmulator boards. FRANK OS derives its application loading, system table, shell, and POSIX compatibility layer from this project.
- Project: FreeRTOS Kernel
- Author: Amazon Web Services
- License: MIT
- Description: Real-time operating system kernel used for task scheduling and synchronization.
- Project: DispHSTX
- Author: Miroslav Nemecek (Panda38)
- License: BSD-3-Clause
- Description: DVI display driver using the RP2350 HSTX peripheral.
- Project: FatFs
- Author: ChaN
- License: FatFs License (BSD-style)
- Description: Generic FAT filesystem module for SD card access.
- Project: pico-sdk
- Author: Raspberry Pi (Trading) Ltd.
- License: BSD-3-Clause
- Description: Hardware abstraction and build system for RP2040/RP2350 microcontrollers.