Chip designer Sonal Pinto is recreating the Arduino-compatible Arduboy handheld console, with one key difference: It's powered by his own RISC-V system-on-chip (SoC), the Kronos Zero Degree (KZD) SoC featuring the Kronos RISC-V core.
"Kronos is 3-stage pipelined in-order RISC-V core," Pinto writes of the processor core they designed atop the free and open source RISC-V instruction set architecture (ISA). "The RISC-V ISA is well suited to be implemented as a classic pipelined RISC architecture, and this core is no exception."
"Now that I knew the core was viable, I designed the project flagship — KRZ (Kronos Zero Degree), a SoC on the iCEBreaker to showcase the Kronos core. 128kB of RAM as 2 contiguous banks of 64KB; 1kB Boot ROM for loading program from flash to RAM, and general purpose registers for warmboot; Configurable UART TX with 128B buffer; Configurable SPI Master with 256B RX/TX buffers, max 12MHz; 12 Bidirectional configurable GPIO, with debounced inputs."
The Kronos core is not the first RISC-V core around, and nor is the KZD the first RISC-V SoC. What is truly interesting in Pinto's work is that it is being used to clone the Arduboy — creating what is effectively a fully-open variant, from the processor upwards.
"The real reason why I built the KRZ was to have it run a native port of the Arduboy! A core can only shine when it runs awesome software," Pinto explains. "When I first saw the Arduboy bootlogo scroll down the OLED, I was like '#$#$ #$## this works!!!.' This is the krzboy project, and is a work-in-progress (more exciting details to follow soon).
"Real talk, I initially started this project to build some street cred as a digital designer (my trade). The RISC-V ISA and the open source community that has grown around it is absolutely beautiful, and I want to be a part of it. If it wasn't for the maturity of the riscv-toolchain and the effort the community has put into it, I wouldn't have attempted to build this core. As a bonus, I also get something neat to present during job interviews, instead of just my prosaic grad school work on formal theory."
More details on the project can be found on Pinto's Hackaday.io page, while the SoC and core have been published to GitHub. Pinto has also published a deep dive into the architecture of the Kronos RISC-V core.