This document outlines the openvela boot process, detailing the Board Support Package (BSP) initialization sequence, the startup script mechanism, and the core function call relationships.

I. Board Initialization Sequence

The openvela system boot-up follows a well-defined Board Support Package (BSP) initialization sequence. The process begins at the kernel entry point, nx_start, and proceeds through several initialization stages within different task contexts before finally entering the idle loop.

Core Initialization Sequence

// --- In Idle Task context ---
nx_start()
  |
  +--> board_early_initialize()
  |
  +--> // Creates the AppBringup_task thread
// --- In AppBringup_task context ---
board_late_initialize()
  |
  +--> // Creates the nsh_task thread
// --- In nsh_task context ---
board_app_initialize()
  |
  +--> rc.sysinit // Script execution
  |
  +--> board_app_finalinitialize()
  |
  +--> rcS        // Script execution
// --- System enters the idle loop ---

The following table details the purpose, execution context, and required configuration for each key function and script in the sequence.

Sequence	Function/Script	Execution Context	Description	Required Kconfig
1	nx_start	Idle Task	The openvela operating system entry point.
2	board_early_initialize	Idle Task	Performs early board-level hardware initialization. Note: This stage runs before core OS components are ready, so it must not call any function that could block or wait for an event (e.g., sem_wait).	CONFIG_BOARD_EARLY_INITIALIZE
3	board_late_initialize	AppBringup Task	Initializes the main board-level drivers. Note: At this stage, core OS components are ready, allowing calls to functions that may involve event waiting.	CONFIG_BOARD_LATE_INITIALIZE
4	board_app_initialize	nsh Task	Called by the nsh task via boardctl (BOARDIOC_INIT) to initialize the application layer. Note: The file system is not yet mounted, so file access is not possible.
5	rc.sysinit	nsh Task	Mounts the file system and initializes core startup services.	CONFIG_NSH_SYSINITSCRIPT
6	board_app_finalinitialize	nsh Task	Performs final board-level initialization, called via boardctl (BOARDIOC_FINALINIT). Note: Used for drivers that depend on file system access (e.g., TP, Charger, Audio PA). These drivers can now directly access files without needing to defer operations via the delayed work queue.
7	rcS	nsh Task	Starts user-space core applications and services, such as miwear and algo_service.	CONFIG_NSH_INITSCRIPT

II. Startup Script Mechanism

Location and Loading

openvela uses the rcS and rc.sysinit startup scripts to configure the system during boot. These scripts are loaded and parsed by the nsh task via the nshlib library. Their locations are specified by the following Kconfig options:

1. CONFIG_ETC_ROMFSMOUNTPT/CONFIG_NSH_SYSINITSCRIPT
2. CONFIG_ETC_ROMFSMOUNTPT/CONFIG_NSH_INITSCRIPT

Typically, the startup scripts reside in the /etc directory. The contents of /etc are compiled and linked with the openvela binary as a ROMFS (Read-Only File System), which is automatically mounted at boot. The related configuration is as follows:

CONFIG_FS_ROMFS=y
CONFIG_ETC_ROMFS=y
CONFIG_ETC_ROMFSMOUNTPT="/etc"
CONFIG_NSH_SYSINITSCRIPT="init.d/rc.sysinit"
CONFIG_NSH_INITSCRIPT="init.d/rcS"

Generation

The contents of the /etc directory are typically generated from a source directory within the board-specific configuration. The genromfs and xxd tools can be used to generate an etc_romfs.c file, which is then compiled into the kernel. For example:

• Generated File: boards/arm/at32/at32f437-mini/src/etc_romfs.c
• Generation Script: boards/arm/at32/at32f437-mini/tool/mkromfs.sh

A more common method is to build the /etc contents directly from a board/arch/board/src/etc directory, such as:

• Example Directory: boards/sim/sim/sim/src/etc

All files within /etc are controlled by the Makefile in the parent directory:

• RCSRCS is used to specify the startup scripts.
• RCRAWS is used to specify other files and directories to be included in /etc.
  

  ifeq ($(CONFIG_ETC_ROMFS),y)
    RCSRCS = etc/init.d/rc.sysinit etc/init.d/rcS
    RCRAWS = etc/group etc/passwd
  endif

III. Call Relationships

The following diagram illustrates the core function call relationships in the openvela boot process, providing a visual overview of the entire sequence.

Note: This diagram is for illustrative purposes and shows the main flow. For precise implementation details, always refer to the latest source code.

IV. References

• For a detailed visual analysis of the NuttX boot process, see Lee Lup Yuen's article: Call Graph for Apache NuttX RTOS.