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Add a Tutorial tree that mirrors the roadmap from Phase 0 through Linux bring-up. Each phase and subphase gets a short learning note with consistent sections for context, goals, new concepts, mental model, learning tasks, pitfalls, tooling, testing, and references. The tutorial material is intentionally explanatory rather than implementation code. It gives a systems-oriented learner enough FPGA, SystemVerilog, RISC-V, firmware, and Linux bring-up context to approach each roadmap phase without turning the notes into copy-paste RTL.
1.7 KiB
1.7 KiB
Phase 16 - Linux Boot Contract
Context
Linux does not start from reset like bare-metal firmware. It expects a specific entry state, memory layout, device tree, and usually firmware services.
Goals
- Define the exact kernel entry ABI.
- Provide a device tree describing the SoC.
- Choose direct M-mode Linux or OpenSBI + S-mode Linux.
New Concepts
- Device tree: data structure describing hardware to the kernel.
- DTB: compiled binary form of a device tree source.
- SBI: Supervisor Binary Interface, firmware API used by S-mode kernels.
- OpenSBI: common RISC-V machine-mode firmware implementation.
- Hart: RISC-V hardware thread, roughly a CPU core/thread.
How To Think About It
This phase is about removing ambiguity before kernel bring-up. If the boot contract is wrong, Linux often just hangs early with little output.
Learning Tasks
- Read the RISC-V Linux boot protocol and list required register state.
- Draft a device tree matching your memory map and interrupt topology.
- Decide whether the first Linux attempt uses direct M-mode or OpenSBI.
Pitfalls
- Passing the wrong DTB address in
a1. - Loading the kernel at the wrong alignment.
- Claiming device-tree compatibility with hardware you did not implement.
Tooling And Testing
- Validate DTS with
dtc. - Keep early console strategy simple and documented.
- Build small firmware checks that print boot parameters before jumping to Linux.
References
- RISC-V Linux boot protocol: https://docs.kernel.org/arch/riscv/boot.html
- RISC-V device-tree CPU bindings: https://www.kernel.org/doc/Documentation/devicetree/bindings/riscv/cpus.yaml
- OpenSBI: https://github.com/riscv-software-src/opensbi