A Resilient System Design to Boot a RISC-V MPSoC

This paper presents a highly resilient boot process design for Ballast, a new RISC- V based multiprocessor system-on-chip (SoC). An open source RISC- V SoC was adapted as a bootstrap processor and customized to meet our requirement for guaranteed chip wake-up. We outline the characteristic challenges of implementing a large program into a read-only memory (ROM) used for booting and propose generally applica-ble workflows to verify the boot process for application specific integrated circuit (ASIC) synthesis. We implemented four distinct boot modes. Two modes that load a software bootloader autonomously from an SD card are implemented for a secure digital input output (SDIO) interface and for a serial peripheral interface (SPI), respectively. Another SDIO based mode allows for direct program execution from external memory, while the last mode is based on usage of a RISC- V debug module. The boot process was verified with instruction set simulation, register transfer level simulation, gate-level simulation and field-programmable gate array prototyping. We received the fabricated ASIC samples and were able to successfully boot the chip via all boot modes on our custom circuit board.