Virtual Jaguar 3.4.0 emulates Atari's voice modem and finds netplay hosts on its own

The libretro Jaguar core adds emulation of Atari's obscure Voice Modem, LAN peer discovery for netplay, texture dumping and more boot ROMs.

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Virtual Jaguar, the libretro core that emulates Atari's ill-fated Jaguar console, has reached version 3.4.0. The headline addition is emulation of the Jaguar Voice Modem, a piece of hardware so obscure that only one retail game ever used it, alongside a netplay discovery system that no longer requires anyone to type an IP address.

The release notes, published on the GitHub release page, call it “the peripheral release”. That is not an exaggeration. Alongside the modem work, this version finishes support for every controller Atari made or planned for the Jaguar, adds a texture dumping and replacement pipeline for HD pack authors, and lets players choose which console boot ROM a cartridge starts from.

Why the Voice Modem needed reverse-engineering, not guessing

The Jaguar Voice Modem, or JVM, was Atari's stab at a voice-and-data peripheral, and Ultra Vortek was the only game that ever spoke to it. According to the release notes, the emulation was built by reverse-engineering the retail ROM rather than working from documentation, and the resulting protocol is not the familiar AT command set most modems used. It is a custom Phylon command set, with 16-bit words sent from the console to the modem, three-byte replies coming back, and a mutual DTMF probe acting as a line-quality check before a call connects. The full decode has been written up in a document shipped with the core, docs/voice-modem.md. The developers say the implementation was verified on two real iOS devices rather than tested only in isolation, and that in-game, a player dials via the numpad at the Ultra Vortek title screen while the other side answers, with the “call” carried over the emulator's existing netplay transport.

Finding a netplay peer without typing an address

The bigger practical change for most players is how two consoles find each other at all. Libretro's core options system cannot present a free text field, so linking two Jaguars previously meant fiddling with a preset, a file, or localhost, and on iOS those were the only choices available. Version 3.4.0 adds an Automatic mode, now the default, which rides an existing frontend netplay session with nothing to configure, plus a LAN discovery mode where hosts broadcast over UDP and simply appear by name in a picker. The notes explain the choice of UDP over the more common Bonjour discovery protocol: RetroArch's iOS and tvOS builds only allow a core to advertise the service types the platform itself already knows about, which blocks a custom Bonjour service, whereas broadcast UDP is permitted. The emulator now narrates on screen what mode has resolved, when a link comes up or drops, and warns if a peer is running mismatched hardware, since a JagLink connection and a Voice Modem connection cannot talk to each other, a failure the developers say used to happen silently.

Peripherals, textures and boot ROMs

The rest of the release is tidying up long-standing gaps. Support for the ST/Amiga mouse, the Tempest rotary controller, the analog driving controller and a working lightgun is now complete, closing what the notes call “the input-device epic”. The analog controller needed particular care: the Jaguar's own silicon has no analogue-to-digital converter on that port, so the real controller carries its own microcontroller, which the emulator now has to answer correctly. A new texture dump mode writes out every unique graphic a game draws as a PNG with a stable content hash, intended for people building HD replacement packs, and a first tier of texture replacement can swap those tiles back in without affecting savestates or netplay determinism, according to the release notes. Cartridges can also now boot from either of the Jaguar's two console boot ROM revisions, Series K or Model M, or a custom image. Discussion of the release is under way on the r/emulation thread, where wider testing of the Voice Modem feature beyond the developers' own setup has yet to appear.

Sources

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