NX-trex

A Vectrex emulator for the Nintendo Switch.

NX-trex is a port of VecX, the classic Vectrex emulator by Valavan Manohararajah, wrapped in a native Switch frontend with a custom menu, SD card cart loading, and analog stick input.

Legal

NX-trex includes the Vectrex BIOS (rom.dat) to ensure the emulator runs on real hardware. On October 27, 1992, Smith Engineering granted the community permission to freely distribute all Vectrex-related materials (BIOS, games, manuals, documentation) for non-commercial purposes. See LEGAL.txt for full details.

Features

• Runs commercial Vectrex cartridges (.vec , 4K-8K)
• Built-in BIOS with Mine Storm
• Native Switch menu with cart browser
• Analog stick input with response curve for precision games
• 2-player mode (one sideways Joy-Con each; menu driven by Player 1)
• SD card cart loading
• Sound via AY-3-8912 emulation

Requirements

• A Nintendo Switch with homebrew enabled (Atmosphère or similar)
• Optionally, Vectrex cartridge dumps in .vec format

Installation

1. Copy NX-trex.nro to sdmc:/switch/ on your SD card.
2. (Optional) Create sdmc:/NX-trex/roms/ and drop .vec files there.
3. Launch NX-trex from the homebrew menu.

The emulator will create sdmc:/NX-trex/ and sdmc:/NX-trex/roms/ automatically if they don't exist.

Usage

On startup you'll see the main menu:

• RUN MINE STORM - boot the built-in game from the BIOS
• LOAD CART - browse and load .vec files from sdmc:/NX-trex/roms/
• 2P MODE: ON / OFF - toggle 2-player mode
• EXIT - quit to the homebrew menu

Controls

1 Player mode:

Switch	Vectrex
Left analog stick	Analog joystick
B / A / Y / X	1 / 2 / 3 / 4
L (or Minus)	Return to menu
R (or Plus)	Quit

2 Player mode (each player holds one Joy-Con sideways: Joy-Con L is rotated -90°, Joy-Con R is rotated +90°):

Joycon L (Player 1)	Vectrex
Left analog stick	Analog joystick
left(down) / down(right) / up(left) / right(up)	1 / 2 / 3 / 4
SL (or Minus)	Return to menu
SR (or Plus)	Quit

Joycon R (Player 2)	Vectrex
Right analog stick	Analog joystick
A / X / B / Y	1 / 2 / 3 / 4

Menu

The menu is always driven by Player 1. In 2P mode Player 1 is the Left Joy-Con (held sideways); the Right Joy-Con (Player 2) is not used by the menu. Navigation is with the analog stick only.

Action	1P mode	2P mode (Player 1 = Left Joy-Con)
Move	Left stick	Left stick (rotated)
Confirm (btn 4)	X	D-Pad Right
Back (btn 1)	B	D-Pad Left
Return to menu	L (or Minus)	SL (or Minus)
Quit	R (or Plus)	SR (or Plus)

Building

Requires devkitPro with switch-dev.

Changes from upstream VecX

NX-trex is not a bit-for-bit copy of VecX. Beyond the Switch frontend, the emulator core itself has been modified in a few places.

CPU (e6809)

• Fixed an uninitialized read path in the 6809 memory decoder that could return garbage for certain unhandled address ranges.
• Consolidated two divergent forks of the e6809.c core into a single source file with a merged interface.
• Corrected the return-value semantics of a small number of condition-code helpers on edge inputs.
• Signature and interface changes to integrate cleanly with the host's function-pointer I/O model.

Sound (e8910)

• The AY-3-8912 core is unchanged; only the output stage differs.
• The mixer output (0..4095, the volume domain) is scaled by 8 to fill signed 16-bit range, then fed to the standard libnx audout path at its native 48 kHz (mono duplicated to stereo), with no external mixer.
• e8910_update() drains every free buffer each 30 fps frame. The device consumes about 1.5 buffers per frame, so refilling only one starved the queue; draining all released buffers keeps it fed.

Everything else

The 6522 VIA, analog integrator, vector generator, and cartridge mapper are unchanged from VecX and behave identically.

TODO

• Verify sound against more carts (Armor Attack and similar)
• Centre the audio output to remove the DC offset / note-onset transients
• Test with more carts, especially edge cases (unusual sizes, non-standard headers)

Changelog

2.0.0

• Added 2-player mode: one Joy-Con per player, held sideways (Joy-Con L is player 1, Joy-Con R is player 2).
• Reworked menu navigation: analog stick only, confirm on button 4, cancel on button 1, and the menu is always driven by player 1.
• Moved return/quit to L/R (SL/SR in 2-player mode).
• Audio fixes: the AY mixer output is scaled to fill 16-bit range without overflowing (the old scale clipped and rasped), and all released audio buffers are drained so the output no longer starves.
• Split the bitmap font and menu helpers out of main.c into font8x8.c and ui.c.

1.0.0

• Initial release.

Credits

• VecX by Valavan Manohararajah, the CPU, VIA, analog, and sound core
• font8x8_basic by Daniel Hepper (public domain), menu font
• libnx / devkitPro, Switch toolchain and runtime
• Vectrex BIOS and games © Smith Engineering / Jay Smith

NX-trex is not affiliated with or endorsed by Nintendo, Smith Engineering, or Jay Smith.