Hecate

USB to PS/2 Keyboard and Mouse Converter for Raspberry Pi Pico

Overview

Hecate is a firmware for the Raspberry Pi Pico (RP2040) that converts USB keyboards and mice to PS/2 protocol. It allows you to use modern USB peripherals with vintage computers and systems that only support PS/2 input devices.

Why Hecate?

Named after Hecate, the ancient Greek goddess of crossroads and liminal spaces. Just as Hecate stands at the intersection of worlds, this project bridges the gap between modern USB devices and legacy PS/2 systems—a converter standing at the crossroads of old and new technology.

Features

USB Host

• Triple USB ports - Native Type-C plus dual PIO-USB ports
• Hybrid USB mode - Use Type-C and PIO-USB simultaneously
• USB hub support - Connect multiple devices via hub on any port
• HID report parsing - Supports both boot protocol and full HID report descriptors
• NKRO support - N-Key Rollover for gaming keyboards

PS/2 Keyboard Emulation

• Full Scancode Set 2 - Complete key mapping including all standard keys
• Extended keys - Navigation, multimedia, and special keys with E0 prefix
• Key repeat (typematic) - Configurable repeat rate and delay
• LED feedback - Caps Lock, Num Lock, Scroll Lock sync with host
• Host commands - Reset, Echo, Identify, Set LEDs, Set Typematic Rate
• Special sequences - Proper Pause/Break and Print Screen handling

PS/2 Mouse Emulation

• Standard 3-button mouse - Left, right, middle buttons
• IntelliMouse - Scroll wheel support (auto-detected)
• IntelliMouse Explorer - 5-button support (auto-detected)
• Stream and Remote modes - Automatic mode detection
• Host commands - Reset, Get ID, Enable/Disable streaming, Read Data, Status request

Status LED

• Connection indicator - LED on when keyboard or mouse is connected
• Activity indicator - LED blinks on keypress or mouse button click
• RP2040-Zero RGB - Green when connected, blue flash on activity
• Pico onboard LED - On when connected, blinks on activity

Pin Configuration

Function	GPIO	Description
UART TX	GPIO 0	Debug serial output
UART RX	GPIO 1	Debug serial input
PIO-USB0 D+	GPIO 2	PIO-USB Port 0 Data+
PIO-USB0 D-	GPIO 3	PIO-USB Port 0 Data-
PIO-USB1 D+	GPIO 4	PIO-USB Port 1 Data+
PIO-USB1 D-	GPIO 5	PIO-USB Port 1 Data-
PS/2 KB DATA	GPIO 11	Keyboard Data line
PS/2 KB CLK	GPIO 12	Keyboard Clock line
PS/2 MS DATA	GPIO 14	Mouse Data line
PS/2 MS CLK	GPIO 15	Mouse Clock line
WS2812 LED	GPIO 16	RGB LED (RP2040-Zero)
Native USB	Type-C	Native USB host port

Supported Boards

Raspberry Pi Pico (default)

• Onboard LED on GPIO 25
• Build with default settings

Waveshare RP2040-Zero

• WS2812 RGB LED on GPIO 16
• Build with -DUSE_WS2812=1

cmake -DUSE_WS2812=1 ..

Building

Prerequisites

• Pico SDK installed
• PICO_SDK_PATH environment variable set
• ARM GCC toolchain

Build Commands

mkdir build
cd build
cmake ..
make -j4

The firmware will be generated as build/hecate.uf2.

Flashing

1. Hold the BOOTSEL button on the Pico
2. Connect to USB while holding BOOTSEL
3. Release BOOTSEL - the Pico appears as a USB drive
4. Copy hecate.uf2 to the drive

Or use the included flash script:

./flash.sh

Release Build

To create a release build with version tracking:

./release.sh

Release files are saved to the releases/ directory with version numbering (e.g., hecate_1_00.uf2).

Debug Output

UART serial console is available on GPIO 0 (TX) and GPIO 1 (RX) at 115200 baud. Connect a USB-to-serial adapter to view debug messages.

Hardware Notes

PS/2 Connections

PS/2 uses open-drain signaling. The DATA and CLK lines should be directly connected to the Pico GPIO pins. The Pico's internal pull-ups are not used; the PS/2 host provides the pull-ups.

PS/2 Connector (female, from device side):
    6 5
   4   3
    2 1

Pin 1: DATA
Pin 3: GND
Pin 4: +5V
Pin 5: CLK
Pin 6: N/C

USB Connections

Each USB port requires D+ and D- connections. The D- pin is always D+ pin + 1.

For a USB Type-A connector:

• Pin 1: +5V (VBUS)
• Pin 2: D-
• Pin 3: D+
• Pin 4: GND

License

MIT License - See LICENSE file for details.

Acknowledgments

This project incorporates code and concepts from:

• ps2x2pico by No0ne - PS/2 protocol implementation and PIO programs

  • Copyright (c) 2024-2025 No0ne
  • Copyright (c) 2023 Dustin Hoffman
  • Licensed under MIT License

• pico-hid-host by Fruit-Bat - HID report descriptor parsing library

  • Copyright (c) 2024 Fruit-Bat
  • Licensed under MIT License

• Pico-PIO-USB by sekigon-gonnoc - USB host implementation using PIO

  • Licensed under MIT License

• TinyUSB by Ha Thach - USB stack

  • Licensed under MIT License

• Raspberry Pi Pico SDK - Hardware abstraction layer

  • Licensed under BSD 3-Clause License