The Raspberry Pi team has released an update to the RP2350 microcontroller with bug fixes, hardening, and a GPIO tweak that will delight retro hardware enthusiasts.

The A4 stepping brings several improvements, including remedies for the glitches [1]identified in the company's 2024 hacking challenge (though a spokesperson was quick to note they all required physical access to the hardware), as well as the documented GPIO pull-up issue that required affected customers to use some extra circuitry and resistors.

Chris Boross, senior sales exec at Raspberry Pi, told us that with the new stepping, the team wanted to deal with the issue and render the additional circuitry unnecessary. "It's a drop-in replacement," he said. "This is something that we always wanted to take care of."

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Customers can swap out the original A2 for the A4 without fuss. However, applications might require recompilation if older versions of the SDK are in use. Boross told The Register that version 2.1 of the SDK, released earlier this year, would be fine, so there's no need to be on the absolute bleeding edge. However, 2.1 is the minimum requirement for compatibility with the A4 stepping.

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Other improvements include support for self-decrypting binaries and newly hardened AES decryption code "with high resistance against side-channel attacks."

The Raspberry Pi team is also launching [5]a new hacking challenge for the RP2350, saying: "We think we've made something resistant to side-channel analysis, and we're challenging people to prove us wrong."

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The last hacking challenge unearthed boot ROM glitches. The team hopes the new one won't turn up something that requires another chip spin. Boross said: "We always knew there was a high likelihood [the 2024 challenge] would result in a chip spin. This new hacking challenge is far less likely to do so."

That said, if hackers do find something in the hardware, then "we're not taking another chip spin off the table, but we're not planning on it any time soon."

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GPIO is now rated as 5 V-tolerant, which opens up some intriguing retro computer applications. Where before buffers and voltage translators were needed for hooking up the [11]Programmable I/O (PIO) , the change means users can go directly to the bus.

"So it just makes it cleaner, simpler, cheaper, and easier to interface the RP2350 with five-volt TTL logic," explained Boross.

Software-defined peripherals are just one use case. The change will also make connecting hardware in the five-volt ecosystem easier.

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"It's going to be fun for retro computing," said Boross, "but also useful in other use cases." ®

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[1] https://www.theregister.com/2025/01/16/raspberry_pi_awards_prizes_for/

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[5] https://github.com/raspberrypi/rp2350_hacking_challenge_2

[6] https://www.theregister.com/2025/06/05/vibe_coding_raspberry_pi/

[7] https://www.theregister.com/2025/05/02/raspberry_pi_cm4_cuts/

[8] https://www.theregister.com/2025/04/02/raspberry_pi_not_affected_by_tariff/

[9] https://www.theregister.com/2025/03/24/raspberry_pi_poweroverethernet/

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[11] https://www.raspberrypi.com/news/what-is-pio/

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[13] https://whitepapers.theregister.com/