OpenSBI Platform Requirements

The RISC-V platform requirements for OpenSBI can change over time with advances in RISC-V specifications and ecosystem.

To handle this, we have two types of RISC-V platform requirements:

1. Base platform requirements which apply to all OpenSBI releases
2. Release specific platform requirements which apply to a OpenSBI release and later releases

Currently, we don't have any Release specific platform requirements, but such platform requirements will be added in future.

Base Platform Requirements

The base RISC-V platform requirements for OpenSBI are as follows:

1. At least rv32ima_zicsr or rv64ima_zicsr required on all HARTs

2. At least one HART should have S-mode support because:

   • SBI calls are meant for RISC-V S-mode (Supervisor mode)
   • OpenSBI implements SBI calls for S-mode software

3. The MTVEC CSR on all HARTs must support direct mode

4. The PMP CSRs are optional. If PMP CSRs are not implemented then OpenSBI cannot protect M-mode firmware and secured memory regions

5. The TIME CSR is optional. If TIME CSR is not implemented in hardware then a 64-bit MMIO counter is required to track time and emulate TIME CSR

6. Hardware support for injecting M-mode software interrupts on a multi-HART platform

The RISC-V extensions not covered by rv32ima_zicsr or rv64ima_zicsr are optional for OpenSBI. Although, OpenSBI will detect and handle some of these optional RISC-V extensions at runtime.

The optional RISC-V extensions handled by OpenSBI at runtime are:

• D-extension: Double precision floating point
• F-extension: Single precision floating point
• H-extension: Hypervisor