Raspberry Pi RP2350 A4 Stepping: Sicurezza Avanzata e Nuove Varianti Flash
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One year after launching the RP2350 dual-core microcontroller, Raspberry Pi has announced significant improvements with the A4 stepping release. This update directly addresses security vulnerabilities discovered during the company’s successful 2024 hacking challenge, while also fixing the notorious E9 GPIO erratum that has been a thorn in developers’ sides.
Key Improvements with the RP2350 A4 Stepping
The new A4 stepping represents a comprehensive security overhaul; most significantly, it resolves multiple security vulnerabilities identified through Raspberry Pi’s “security through transparency” approach, where the company actively invites hackers to find weaknesses before widespread deployment.
Security enhancements on the RP2350 A4 stepping
- Boot ROM vulnerabilities fixed: Errata 20, 21, and 24, all discovered during the 2024 hacking challenge, have been patched.
- OTP security improvements: Erratum 16, relating to OTP behavior during power removal, has been addressed through wrapper circuitry changes.
- New defensive strategies: The boot ROM now implements additional protections to reduce future exploit likelihood.
- Hardened AES implementation: A power-hardened AES cipher now handles firmware decryption with resistance to side-channel attacks.
Hardware Fixes
The most welcome news for hardware designers is the resolution of Erratum 9 – the GPIO pad high-impedance issue that prevented proper pull-up behavior. This fix eliminates the need for additional external circuitry and resistors that developers have been using as workarounds.
Drop-in Compatibility
The A4 stepping functions as a direct replacement for the original A2 version, requiring no hardware changes. However, firmware compatibility requires pico-sdk version 2.1.0 or later. Earlier SDK versions will need recompilation to work with A4 devices.
Introducing RP2354: 2MB Flash Variants
Alongside the A4 stepping, Raspberry Pi introduces the RP2354A and RP2354B variants, featuring integrated 2MB Winbond flash memory stacked in-package. These new parts address a long-standing customer request for reduced PCB complexity and sourcing effort.
RP2354 Benefits:
- Simplified design: No external flash components required.
- Modest cost increase: Only $0.20 premium over equivalent RP2350 parts.
- Pin compatibility: Direct replacement for 60-pin RP2350A and 80-pin RP2350B.
- Reduced PCB area: Eliminates QSPI flash footprint and routing requirements.
The integrated flash solution provides an attractive middle ground between the flexibility of external memory and the convenience of all-in-one packages, particularly for cost-sensitive applications requiring moderate storage capacity.
5 V Tolerance Officially Confirmed
In welcome news for retro computing enthusiasts and industrial applications, the RP2350 has been officially qualified as 5V tolerant after extensive testing. This certification opens new possibilities for interfacing with legacy systems and industrial equipment.
5 V Interface Requirements:
- VDDIO must remain powered when 5 V is applied to GPIO pads
- Proper power sequencing prevents pad damage
- Updated datasheet provides detailed specifications and guidelines
New RP2350 A4 Stepping Hacking Challenge
Building on the success of the 2024 challenge, which yielded four valid security exploits (each winner receiving the full $20,000 prize), Raspberry Pi launches a new challenge targeting side-channel attacks on AES decryption.
The challenge specifically focuses on the hardened AES implementation used for firmware decryption during boot. This represents a significant escalation in difficulty compared to the previous OTP-based challenge, requiring sophisticated power analysis and electromagnetic techniques.
Challenge Details:
- Prize: $20,000 for successful side-channel attack.
- Target: Power-hardened AES decryption during boot.
- Partners: Thomas "stacksmashing" Roth and Hextree.io team.
- Scope: Practical attacks that can extract encryption keys or firmware.
Industry Impact and Developer Considerations
Raspberry Pi's transparent approach has proven effective at identifying and fixing vulnerabilities before widespread deployment.
For Current RP2350 Users:
- Immediate benefit: A4 parts available now from approved resellers.
- Migration path: Existing A2 designs work without modification.
- Software update: Ensure pico-sdk 2.1.0+ compatibility.
For New Designs:
- RP2354 consideration: Evaluate integrated flash benefits for new projects.
- Security features: Leverage improved boot ROM and AES capabilities.
- 5 V compatibility: Simplified interfacing with higher-voltage systems.
SDK and Toolchain Updates
Concurrent with the hardware release, Raspberry Pi has introduced pico-sdk version 2.2.0 with enhanced security features:
- Hardened AES: Production-ready side-channel resistant implementation.
- Self-decrypting binaries: Support for AES-encrypted firmware with embedded bootloader.
- New examples: Encryption, OTA updates, and UART bootloading demonstrations.
- Documentation improvements: Enhanced security guidance and best practices.
Beyond the Lab: Real-World Impact
The RP2350's commercial success extends far beyond maker projects. Real-world deployments now span drones, industrial automation, synthesizers, electronics development tools, space hardware, premises management, and robotics, demonstrating the chip's transition from hobbyist favorite to industrial workhorse.
Raspberry Pi’s ecosystem expansion continues with the Radio Module 2, launched in June, providing pre-certified wireless connectivity specifically designed for RP2040/RP2350 products. This addresses a critical need for IoT applications while simplifying regulatory compliance for commercial deployments.
The company’s commitment to the security research community remains strong, with plans to return to DEF CON’s Embedded Systems Village for demonstrations and workshops. This grassroots engagement strategy continues to yield valuable security insights while building developer mindshare.
For commercial integrators, Raspberry Pi has enhanced its Global Market Access support, signaling serious intent to capture industrial design wins. The A4 stepping's availability through JLCPCB particularly benefits the maker-to-manufacturer pipeline, where prototypes often evolve into production runs.
Perhaps most intriguingly, the new AES implementation incorporates per-device salt values stored in OTP memory, making each RP2350 cryptographically unique. This sophisticated approach to embedded security positions the chip for applications where device-level authentication and tamper resistance are paramount — a growing requirement in our increasingly connected world.
Looking Forward
The A4 stepping establishes a new baseline for embedded security in the Raspberry Pi microcontroller space, which creates a compelling value proposition for security-conscious applications.
The new hacking challenge targeting side-channel attacks acknowledges that security is an ongoing process rather than a destination. By continuously testing and improving their implementations, Raspberry Pi positions the RP2350 as a genuinely secure foundation for embedded applications.
For designers choosing microcontrollers for security-sensitive applications, the RP2350 A4’s combination of proven security testing, transparent vulnerability disclosure, and rapid remediation makes it an attractive option in an increasingly threat-conscious world.
With its 5 V tolerance and optional 2 MB of flash memory, it opens up all kinds of possibilities for one of my favorite applications: retro computing. Think cartridge emulators, extra memory, or even a graphics controller with HDMI/DVI output.
What are you excited about in this release? Let me know in the comments below!
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