Hands-On with the PiStorm, the Ultimate Raspberry Pi-Powered Accelerator for Your Commodore Amiga

Costing as little as $13 and playing host to a Raspberry Pi, this could be the biggest bargain in Amiga accessories in three decades.

Gareth Halfacree
3 years agoRetro Tech

Launched in 1985 with the Amiga 1000, Commodore's Amiga range of personal computers was a revolution in the market — but one which did not save Commodore from closure. That, though, is not the end of the story: Amiga fans abound all around the world, and Amiga-compatible hardware is still being produced to this day.

Much of this hardware, sadly, is extremely expensive — out-priced only by original accelerators and other increasingly-rare add-ons. The PiStorm, the brainchild of engineer Claude Schwarz, is different: This accelerator add-on costs as little as $13 fully-assembled, and only needs a Raspberry Pi single-board computer adding to the top in order to bring classic Amiga hardware bang up-to-date.

For anyone with an Amiga 500, Amiga 500 Plus, Amiga 2000, or another model and a willingness to work alongside the project's creator to iron out bugs and extend the number of platforms supported, the PiStorm is likely to prove a must-have add-on.

The Hardware

A Commodore Amiga 500, introduced after the launch-day Amiga 1000 as a cost-reduced and more compact machine priced for home use, is by modern standards no racehorse: The machine was built around a Motorola 68000 processor running at 7MHz alongside a custom chip family known as Paula, Denise, and Agnus and with just 512kB of RAM — upgraded to 1MB in the later Amiga 500 Plus, with memory expansion boards one of the most popular add-ons of the day.

The PiStorm is designed to upgrade an Amiga — primarily the 500, 500 Plus, and 2000, though with the potential for other models and even alternative 68000-based machines in future updates, offering hope for those looking to take a classic Mac up a notch or two — at as low a cost as possible. The four-layer board itself is extremely simple, combining a few bus switches and flip-flops with an Intel Altera MAX II complex programmable logic device (CPLD) — plus pin headers, a regulator, and a few passives.

The CPLD is there to act as glue logic between the Amiga and a Raspberry Pi single-board computer which mates into the top of the PiStorm via its GPIO header. No other wiring is required: Just pop the 68000 out from the socket in the Amiga motherboard, insert the PiStorm in its place, add the Raspberry Pi and microSD card, and you're ready to start configuring your soon-to-be-much-faster Amiga.

There is one minor catch: At the time of writing, the PiStorm exclusively supported the Raspberry Pi 3 Model A+, with the Model B+ a possibility if you're willing to use a GPIO header extension to provide additional clearance to lift taller components away from the Amiga motherboard. Schwarz has shown off work which gets the considerably more powerful Raspberry Pi 4 Model B and the compact but equally impressive Raspberry Pi Compute Module 4 working as PiStorm daughterboards — but support was not yet publicly available and was not tested as part of this review.

One final thing which sets the PiStorm apart from its competition in the Amiga acceleration market, beside its impressively low price: It's open hardware. In fact, having your own boards produced from the supplied design files is one of the only ways to get your hands on one: Schwarz frowns upon commercial exploitation of his designs, meaning you won't find any on sale at retail. For those who don't want to wrestle with minimum order quantities, the PiStorm community hosts regular group buys — though CPLD component shortages of late have seen these spaced further and further apart.

The Software

The hardware is only part of the PiStorm, though. Switch your Amiga on, and you'll be presented with a blank screen. The secret to getting past this: Emulation. The PiStorm handles communication between the real Amiga hardware and the Musashi emulator, which then pretends to be a Motorola 68000 processor — or a 68010, 68020, 68030, 68040, and a small handful of other processor variants, with or without floating-point unit (FPU) coprocessor.

Just as the hardware is presented as a do-it-yourself offering, you'll find no pre-configured SD card images to accomplish this. Instead, the documentation walks you through installing a Linux operating system — Raspberry Pi OS Lite recommended — onto a microSD and then cloning and compiling the source from the PiStorm GitHub repository. Once that's done, you'll need to find a Kickstart ROM: The PiStorm is designed to load a ROM dump file — legally obtainable from Amiga specialist Cloanto for a fee, or you can dump them from your Amiga with a little effort. While it is also supposed to be able to boot from physical ROMs installed in the Amiga if no dump file is present, that process failed on the Amiga 500 Plus with Kickstarter 2.04 used for this review.

At a $13 price point, plus the cost of the Raspberry Pi, that would be enough: A readily-available replacement CPU which offers improved performance over the stock 7MHz Motorola 68000. Emulating a CPU is only a fraction of what the PiStorm offers, however. The same software can be configured to act as a RAM expansion, turning up to 136MB of the Raspberry Pi's RAM into high-speed Zorro II and Zorro III expansion RAM — a big improvement over the stock 512kB or 1MB, and far beyond anything you could manage with SIMM-based RAM board add-ons at anything close to an affordable price point.

That's all impressive enough, but the PiStorm still isn't done. The board acts as a real-time clock, synchronising the Amiga's internal clock with the one on the Raspberry Pi — which is, in turn, set via NTP over the network. There's also IDE and SCSI hard drive emulation, which can be pointed at any block device or a disk image on the Raspberry Pi's microSD card — giving the Amiga effectively unlimited storage capabilities.

The feature list doesn't stop there. For those familiar with configuring an Amiga, it's possible — though a little fiddly — to set the PiStorm up as a retargetable graphics (RTG) card. When you've got this up and running — which requires you to install drivers on the Amiga side as well as set the emulator up on the Raspberry Pi side — you unlock high-resolution, high-colour-depth graphics which are output on the Raspberry Pi's HDMI port in stunning fidelity.

There's still more: A keyboard and mouse connected to the Raspberry Pi's USB port can be passed through to the Amiga. A feature currently in development aims to bridge the Wi-Fi network on the Raspberry Pi with the Amiga, too, giving it network access which is indistinguishable from a native connection to any software you might run.

In short: The PiStorm is a one-stop shop for the overwhelming majority of upgrades a classic Amiga might require.

The Conclusion

That's not to say the PiStorm is without its problems. The first is a question of necessity: By replacing much of the Amiga's own hardware with emulated equivalents, it could be argued you might as well go the whole hog and simple emulate the entire Amiga. There are certainly no shortages of Raspberry Pi-compatible Amiga emulators, and most offer equivalent performance or better to the PiStorm — with the added advantage of taking up a lot less desk space.

Another is both the software and hardware are very much a work in progress. Getting started can be daunting, even if you're well-versed in the Amiga world, though the documentation is backed by a vibrant and helpful community Discord chat server with members always happy to help a newcomer out where possible.

There's the potential for microSD card corruption, too. The PiStorm, and by extension the Raspberry Pi, is powered from the Amiga motherboard. When you switch the Amiga off, the Raspberry Pi loses its power without going through a safe shutdown process. You could mount the filesystem as read-only to avoid this, but then you won't be able to make use of the hard drive image support. There's also a noticeable delay in start-up, with the Raspberry Pi having to boot its operating system and load the emulator before the Amiga can start using it as a CPU.

These points aside, it's hard not to be excited by the PiStorm. Progress on the project is constant and ongoing, and today's crash may well be solved tomorrow. The planned release of Raspberry Pi 4 and Compute Module 4 support will boost performance still further, and there is work afoot on developing PiStorm boards for other Amiga systems — including one which would install in the trapdoor of an Amiga 1200.

At $13, too, the PiStorm is unlikely to be beaten on a price-performance front any time soon. Excluding the cost of the Pi, it's cheaper than most 1MB memory expansions; even allowing a generous $30 for a Raspberry Pi 3 Model A+ and microSD card on top, it's a quarter the price of something like Individual Computers' ACS500plus while offering dramatically better performance and otherwise-missing features like RTG support. If you find a better-value Amiga add-on than the PiStorm, buy it.

More details on the project, plus all source code and hardware files, can be found on the PiStorm GitHub repository.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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