Jesse Taube Gets Linux Up and Running on the Raspberry Pi RP2350's Hazard3 RISC-V Cores
This Buildroot-based basic Linux distribution runs natively on the RP2350's Hazard3 RISC-V cores — albeit not very quickly.
Developer Jesse Taube has become the first to successfully boot a minimal Linux distribution on the Raspberry Pi Pico 2's RP2350 microcontroller — taking advantage of the chip's new open source Hazard3 RISC-V cores to run software more commonly associated with application-class processors than microcontrollers.
"Someone is already running RISC-V NOMMU Linux on [the] RP2350," writes Raspberry Pi principal hardware engineer Luke Wren, who brought the project to our attention and the designer of the Hazard3 cores in the company's new RP2350 microcontroller, on Twitter. "[I] knew I was going to get sniped on that one."
Raspberry Pi launched the RP2350 family, and the new Raspberry Pi Pico 2, earlier this month, offering a major update to the RP2040 which near-doubles the available static RAM (SRAM) and pairs two higher-performance proprietary Arm Cortex-M33 cores with two free and open source Hazard3 RISC-V cores. It's the latter that are the target of Taube's efforts to run Linux on the chip, building on earlier efforts to boot the kernel on microcontrollers including the RP2040 which had to emulate the RISC-V architecture — where the RP2350 can run RISC-V code natively.
There are a few caveats to being able to run Linux on a RISC-V microcontroller rather than an application-class processor, though. The first is a lack of memory management unit (MMU), meaning a specific version which does not rely on the presence of an MMU is required. The second is that even after almost doubling the SRAM on the RP2350 over the RP2040, 520kB is not going to be enough — an issue handily worked around by the RP2350 now supporting up to 16MB of pseudo-static RAM (PSRAM) alongside 16MB of off-chip flash storage.
Taube's basic Buildroot-based Linux distribution, then, won't run on an unexpanded Raspberry Pi Pico 2 — a low-cost development board which lacks PSRAM expansion — but has been confirmed as working on the SparkFun Pro Micro RP2350, one of a growing number of third-party alternatives which pair the chip with 16MB of flash and 8MB of PSRAM.
Instructions for building the distribution are available on Taube's GitHub repository.