firmware-boot-chainlisted

# Firmware Boot Chain ## Overview A boot chain is a relay of stages, each responsible for setting up just enough state to hand control to the next: ROM to firmware (SBI/UEFI), firmware to bootloader, bootloader to OS. Every handoff has a contract: where the next stage lives, what registers/tables it expects, and what memory is already set up. **Core principle:** Each stage owns a contract with the next. Most boot failures are a broken contract at exactly one handoff, so isolate which handoff fails before theorizing about the stage itself. ## When to Use - Writing or porting firmware (RISC-V SBI, UEFI services, ACPI table provision) - Chaining a bootloader (Limine, GRUB, U-Boot) into an OS kernel - A stage loads but the next never starts, or starts and immediately faults - Adding measured boot / TPM PCR extension to the chain - Discovering peripherals from a device tree or ACPI at firmware time ## Map The Handoffs First Write down the relay before debugging: ``` ROM -> firmware (SBI/UEFI) -> bootloader -> OS kernel provides: SBI calls, loads: expects: a0=hartid, memory map, ACPI/DTB kernel+initrd a1=DTB/ACPI ptr, MMU off ``` For each arrow, name: the entry address, the register/pointer contract, and the memory/translation state. The failing arrow is your bug location. ## Firmware Responsibilities - **Provide the platform description.** Hand the next stage a device tree (DTB) or ACPI tables describing memory, CPUs, and peripherals. Prob