This repository contains code and config to build a handheld ZX Spectrum (emulated) on a Raspberry Pi Zero. The full project is documented on Instructables.com: https://www.instructables.com/id/Pocket-ZX-Handheld-ZX-Spectrum/
The keyboard matches the original ZX keyboard layout and is built with an Arduino Pro Micro. It also has a joypad control with a 5-way switch and two action buttons. These will function as either cursor key presses, a USB joystick or a USB mouse depending on which mode it's in. The mode is toggled by pressing the main action button in combination with either the left (joystick) or right (mouse) shift key.
This script watches for a low signal on GPIO3 and initiates system shutdown when it sees one.