Linux_SDK_V0.9.5

docs/platform_requirements.md

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+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 or rv64ima 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 or rv64ima 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