Reboot and power-off

pbl/kernel/reboot.h restarts or powers off the system:

• pbl_reboot() restarts in order;

• pbl_power_off() powers off in order, and restarts if that fails;

• pbl_reboot_emergency() resets at once, for contexts where nothing else can be trusted, e.g. a fault handler or the reset-buttons back door.

Code that must shut down before the system goes away registers a handler with PBL_SYS_OFF_HANDLER_DEFINE(), for one of four modes:

Handlers of a mode run highest priority first. A restart or power-off handler that returns has declined or failed, and the next one runs; once none is left, the kernel resets the SoC.

Prepare handlers only run on the first request, made from a thread with interrupts and the scheduler unlocked. A request from an interrupt, with interrupts locked or from within a handler skips them and goes straight to the restart or power-off handlers, which therefore run in the context of the request and must check it before blocking.

The final reset is the SoC’s pbl_soc_reset() when it selects CONFIG_SOC_HAS_RESET, e.g. SF32LB52 resets through its PMU and the POSIX host restarts the process; otherwise the architecture’s, the NVIC system reset on Cortex-M.

The firmware’s handlers:

Reboot reasons and boot bits stay firmware policy: callers set them before calling into the kernel.