SideTNFS

What is SideTNFS?

SideTNFS is alternative, open-source firmware for the Raspberry Pi Pico W used on SidecarTridge hardware. Through a component called GEMDRIVE, it makes network storage and local storage available to an Atari ST as ordinary GEMDOS drive letters — the same kind of drive letter TOS already uses for a floppy or hard disk.

In practice, that means the Atari can use files and programs straight from the network or an SD card, without needing floppy disk images or a traditional Atari hard-disk image to hold them.

SideTNFS started out from the original SidecarTridge firmware and has since been significantly simplified and refocused around one job: reliable network and local drives. It concentrates on:

• TNFS network drives
• GEMDRIVE integration
• Configurable drive letters
• Optional SD storage
• The built-in SETTINGS drive
• Wi-Fi connectivity
• RTC / NTP clock synchronization
• On-Atari configuration through SIDETNFS.PRG

The original SidecarTridge hardware and firmware architecture are the foundation SideTNFS was built on — full credit for that groundwork belongs to the SidecarTridge project (see Credits and open source).

How it works

1. Atari GEMDOS
2. GEMDRIVE
3. SideTNFS on Pico W
4. Wi-Fi / TNFS server

1. An Atari program asks for a file through GEMDOS, exactly as it would for a floppy or hard disk.
2. GEMDRIVE, running as part of SideTNFS, intercepts that request.
3. The Pico W translates the request into the TNFS network protocol.
4. The file is read from the TNFS server over Wi-Fi.
5. To the Atari, the whole exchange feels like talking to a normal hard disk.

The Atari itself never needs a TCP/IP stack, a modern network driver or any extra networking software — SideTNFS handles the network side entirely on the Pico W.

Installing and updating the firmware

Never insert or remove SideTNFS while the Atari is switched on.

1. Switch the Atari off.
2. Fully disconnect SideTNFS from the Atari.
3. Connect the Pico W to a computer over USB while holding down the BOOTSEL button.
4. Copy sidetnfs_production.uf2 onto the RPI-RP2 drive that appears.
5. Unplug the USB cable.
6. With the Atari still off, plug SideTNFS back in.

For the full walkthrough, including troubleshooting, see the firmware update guide on GitHub. Wi-Fi and drive settings are stored separately from the firmware image and are preserved across a normal update.

Drive management

Up to eight volumes can be active at the same time, in addition to the built-in SETTINGS drive. Each configured drive has:

• a drive letter;
• a recognizable nickname;
• a backend type — TNFS or local SD;
• a TNFS hostname or IP address (for TNFS drives);
• a UDP port (for TNFS drives);
• a mount path.

Out of the box, drive N: is already configured this way, pointing at a public, read-only RetroLoft TNFS test server — so you can try SideTNFS immediately, without setting up a server of your own first. It's just a starting point: change its settings, disable it, or remove it from SIDETNFS.PRG, and add your own TNFS or SD drives instead, for example:

S: is the read-only SETTINGS drive that SideTNFS always provides. It gives access to SIDETNFS.PRG and to on-cartridge documentation, so the tools to configure SideTNFS are always available, even before any network drive is set up.

Hostnames and DNS

You can point a TNFS drive at a plain IP address:

192.168.178.10

or at a hostname:

tnfs.example.org

SideTNFS resolves hostnames via DNS. If a configured hostname can't be found, that drive shows a readable NET_ERR.TXT file describing the error instead of simply failing silently.

RTC and NTP time sync

• SideTNFS can fetch the current time over NTP when it starts up.
• That time can then be used to set the Atari's own clock.
• You configure a fixed UTC offset by hand, to match your local time zone.
• Automatic time zones and daylight-saving switches are not supported yet.

Factory reset

If your configuration ever becomes unreachable, or you just want to start over, you can reset SideTNFS back to its factory default at any time — no computer or SIDETNFS.PRG needed:

1. Switch the Atari off, then on again, so the Pico goes through a fresh boot.
2. Press and hold the SELECT button on the SideTNFS cartridge as the Atari powers back on, and keep holding it.
3. The onboard LED lights up to confirm the reset is in progress.
4. Keep holding SELECT for a full 10 seconds. SideTNFS then rewrites its configuration back to the factory default — drive N: pointing at the public RetroLoft TNFS server — and restarts on its own.

Releasing SELECT before the 10 seconds are up cancels the reset — nothing is changed.

Downloads

Join the community

There's a Discord server dedicated to SideTNFS — the place to share your setup, ask questions, report bugs, and hear about new firmware releases first.

Status and limitations

• SideTNFS is a hobby project, still under active development.
• Filenames are currently limited to the classic Atari 8.3 format.
• Firmware installation is always manual — nothing is installed automatically.
• The UTC offset is fixed and set by hand; there's no automatic daylight-saving support yet.
• Compatibility outside the tested configurations listed above may vary.
• TNFS is intended for trusted networks, or for public servers that are deliberately offered read-only.
• The public RetroLoft TNFS test server is for testing and demos only — its contents may change or be removed at any time, and it should not be used to store data.