Pmic panel

gk and gkos

This respository provides PCB schematics, firmware and debugging support for the gkv4 handheld game console and its operating system, gkos. For the original STM32H7S7-based gk, see README-v3.md.

gkv4 represents a significant upgrade over the original gk with improved speed, a bigger screen, more gamepad buttons and hardware-accelerated 3D rendering.

Videos of the gkv4 in action

Overview

gkv4 is a small, battery powered handheld gaming console running on a STM32MP2 MPU (dual Cortex-A35 cores with additional Cortex-M33 core). It runs a custom OS called gkos which allows near-instantaneous (MCU-like) cold boot times but is powerful enough to run most POSIX userspace applications. See https://github.com/jncronin/gk-userland for the userland support including cross GCC toolchains and useful libraries. https://github.com/jncronin/gk-repo contains all the userspace code including ports of various emulators, games and utilities.

Game/emulator support:

• Mednafen for NES, SNES, SMS, MD and Lynx support
• Hatari for Atari ST
• PCSX_rearmed for PS1
• Mupen64plus (see fork at https://github.com/jncronin/mupen64-combined) for N64 (GPU-accelerated)
• Atari++ for Atari XL
• DOSBox-X (achieves 25000 cycles/second, 199561 parrots, 74 XT on speedtst.com, roughly 486 50 MHz equivalent)
• Native ports of:
  • Neverball/neverputt (GPU-accelerated with tilt support)
  • Tuxracer (GPU-accelerated)
  • Doom (sdl2-doom)
  • Quake (ChocolateQuake)
  • Descent (ChocolateDescent)
  • koules

Hardware Specifications

PCBs, schematics and case STL files are available in https://github.com/jncronin/gk/tree/main/gk-pcbv4.

• STM32MP255D processor with variable clock rate (defined on a per-game basis). Debug and trace ports exposed.
• LPDDR4 RAM (1 GiB in current version)
• Lithium ion battery (10,000 mAH in current version) with USB-C charging via BQ25601, state of charge monitoring via MAX17048 and current sensing via INA236
• 800x480 5 inch touchscreen (ER-TFT050-6). Hardware scaling support via STM32MP2 LTDC peripheral.
• Micro SD for storage with voltage switch support
• Wifi/Bluetooth module attached via M.2 E-key interface (e.g. EAR00389 module)
• Gyrometer/accelerometer + optional magnetometer for tilt interface
• Headphone + internal speaker audio out via TAD5112
• Multiple controls including:
  • Left and right analog sticks (programmable as digital on per-game basis)
  • ABXY + DPAD buttons
  • Start + select buttons
  • Analog throttle controller
  • Volume up/down (can be programmed as additional game inputs)
  • Menu button (opens OSD)
  • Left/right trigger + bumper buttons on back of device
• Battery backup for RTC

Total current draw is heavily dependent on screen brightness but is typically 1.5W or less at full CPU + GPU load with medium brightness, and max ~2W at full brightness.

Software

gkos is a custom OS written from scratch in C++. It is available in the https://github.com/jncronin/gk/tree/main/Firmware-v4 directory. Features:

• Armv8-A SMP scheduler with multiple active processes + threads
• Syscall interface with wrappers for most POSIX functions
• High resolution (10 ns precision) timer provided to games
• pthread support including threads, mutexes, semaphores, conditions, rwlocks and barriers
• A port of the etnaviv GPU driver allowing hardware-accelerated OpenGL
• Driver for Infineon CYW43439 chipset and IPv4 network stack
• SD card (with UHS-I mode support) with Ext4 (Lwext4) and FAT (fatfs) drivers
• USB driver allowing the device to present itself as a mass storage device to allow provisioning the internal SD card
• Offloading of all input tasks, including tilt sensor and touch screen filtering, to Cortex-M33 core

Examples

Tuxracer using the GPU for rendering:

Tuxracer with the OSD overlay (handled by the gk-supervisor process in the (https://github.com/jncronin/gk-userland) repo) showing current system health, battery and cpu usage: