Our favourite thing about reading the brand-new issue of Raspberry Pi Official Magazine, out now, was learning that a special 30th-anniversary edition of DOOM has been released for SNES, and that an RP2350 microcontroller chip runs the custom hardware you play it on.
Did you know that you can still technically make games for old consoles? It’s been a popular thing to do for special editions and anniversaries (promo material for the film Sonic the Hedgehog 3 was even distributed on working Mega Drive / Genesis cartridges). Now it’s the turn of DOOM on SNES, celebrating its 30th anniversary with an updated re-release.
The RP2350 chip replaces — and upgrades — a Super FX chip; it slots into the original SNES hardware and runs without any modding to the console
“We’ve updated and expanded the game with tons of new features, including 14 new levels, improved frame rate and performance, added circle-strafing, and even vibration effects with our new rumble game controller.” Randal Linden of Limited Run Games (LRG) tells us. “The final project uses custom software, tools, firmware, and hardware to create a unique cartridge that works in any Super Nintendo!”
That custom hardware? An RP2350 microcontroller chip, of course.
Super effects
DOOM on SNES was one of the few games to make use of the Super FX chip created for Star Fox (named Starwing in the UK, for weird legal reasons). This resulted in an extra hurdle in creating new, compatible carts for 30+-year-old consoles.
“[The Super FX chip] is a high-speed RISC co-processor that can be used to accelerate and optimise game logic, math, and graphics rendering,” Randal tells us. He would know: he was basically a one-man team behind the original port to SNES. “When we started working on DOOM SNES 2025, our initial focus was on FPGAs to simulate the Super FX chip, but the RP2350 offered advantages that were impossible to resist: first and foremost was the lower cost of the device, both in terms of production but also for development. Next, the numerous GPIOs and efficient PIO programs enabled us to interface the various memory devices used by the cartridge hardware with the Super NES easily and effectively. Finally, the Raspberry Pi SDK is open source and fully documented, which made our bring-up process nice and easy.”
The proof of concept was a little system nicknamed Imp, one of the enemies in DOOM
To prove the concept would work, LRG put together a mini console that they referred to as Imp, using off-the-shelf parts and a Raspberry Pi Pico 2.
“We were able to prove our new ‘FX 3’ system was rendering and playing the game properly, even though at this point we weren’t connected to a SNES. We could also run lots of metrics and debugging quickly to get the FX 3 core stable,” Randal mentions. The original SNES port used a slightly upgraded version of the Super FX chip created after Star Fox, colloquially referred to as Super FX 2, hence the FX 3 moniker. “We then designed our initial SNES PCB designs around socketing a Pimoroni PGA2350; it was a great way to prove the concept was then able to run on a SNES itself.”
Rip and tear
According to Randal, RP2350 has three main functions in the final product: it acts as a high-speed interface to multiple memory devices, simulates the Super FX chip, and performs ‘graphics format conversion operations’.
“We have a pre-production tool which takes the Super NES program executable code, processes it, and generates C source code which is then compiled using the Raspberry Pi Pico SDK,” Randal explains. “The resulting program includes logic which sets up PIO and DMA chains to respond to memory accesses in parallel with the Super FX simulation. After the frame buffer is generated by the Super FX simulation, the graphics conversion logic processes the image from its chunky graphics format into the required Super NES planar format.”
The packaging apes the Super Nintendo game boxes of the time
Creating the game like this also allowed them to add more content that wouldn’t have fit on the original cart — supposedly only 16 bytes were free when it was released.
Playing with super power
“DOOM is widely recognised as one of the greatest games of all time, but when it first came out, the best (and only) way to play the game was using an expensive PC,” Randal says. “At the time, many people didn’t have a high-end computer, but they did have a Super Nintendo, so it was for them that I developed DOOM for SNES.”
It is much more powerful than any game released during the original run of the SNES
The game itself will be out and ready to slam into your slightly yellowed Super Nintendo later this year. The moons of Mars are waiting.
Raspberry Pi Official Magazine #157 out NOW!
You can grab the latest issue right now from Tesco, Sainsbury’s, Asda, WHSmith, and other newsagents, including the Raspberry Pi Store in Cambridge. It’s also available from our online store, which ships around the world. And you can get a digital version via our app on Android or iOS.
You can also subscribe to the print version of our magazine. Not only do we deliver worldwide, but people who sign up to the six- or twelve-month print subscription get a FREE Raspberry Pi Pico 2 W!
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Source: https://www.raspberrypi.com/news/play-a ... of-rp2350/