Open-source and collaborative development is now standard practise in the software world – Linux being an example. While there have been hardware efforts, such as OpenRISC and Opencores, open-source hardware has gained the most traction at the board level. Examples include Arduino and Raspberry Pi, for which the PCB designs are publicly available. However, the chips on which those boards are based have remained proprietary.
Now a team led by ETH Professor Luca Benini, has put into the public domain the full design of one of their microprocessor systems, a derivative of the PULP (Parallel ultra low power) project.
The 32-bit PULPino is designed for battery-powered devices with extremely low energy consumption. The arithmetic instructions are also open source: the scientists made the processor compatible with an open-source instruction set – RISC-V – developed at the University of California in Berkeley (see India prepares RISC-V processors ).
PULPino is a simplified version of the more general PULP, in that it has a single processing element rather than a cluster of four processing elements and has simplified instruction and data RAMs and was implemented in FPGA in 2015. According to presentation materials (downloadable from www.pulp-platform.org) the PULPino core is called RI5CY and is a four-stage in-order pipeline implementation of RISC-V.
The core which is compared to a Cortex-M4 from ARM, has an instructions per cycle figure close to 1, support for the base integer instruction set (RV32I), compressed instructions (RV32C) and partial support for the multiplication instruction set extension (RV32M). It implements non-standard extensions for hardware loops, post-incrementing load and store instructions, ALU and MAC operations. To allow embedded operating systems such as FreeRTOS to run, a subset of the privileged specification is supported. When the core is idle, the platform can be put into a low power mode, where only a simple event