Boot Flow

Categories:

• XWOS

  2 minute read  

XWOS Boot Flow

flowchart LR
    Pre-initialization --> Initialization --> Post-initialization --> Main

    subgraph Pre-initialization
        direction TB
        exc["Exception Init"]
        exc["FPU Init"]
        exc["Memory Init"]
    end

    subgraph Initialization
        xwos_init["xwos_init()"]
    end

    subgraph Post-initialization
        direction LR
        device["Device Driver Init"]
        mm["Dynamic Allocator Init"]
    end

    subgraph Main
        direction LR
        skd_init["Init Scheduler: xwos_skd_init_lc()"]
        thd["Create Threads"]
        skd_start["Start Scheduler: xwos_skd_start_lc()"]
    end

XWOS divides the initialization flow into four phases:

• Pre-initialization Phase (user-defined): xwos_preinit()
• Initialization Phase (XWOS-defined): xwos_init()
• Post-initialization Phase (user-defined): xwos_postinit()
• Main Function Phase (user-defined): xwos_main()

Pre-initialization Phase

In the pre-initialization phase, the user must provide the function definition: void xwos_preinit(void):

• Low-level CPU architecture initialization must be completed, e.g., interrupt initialization, floating-point unit initialization, etc.
• Memory initialization and data section relocation must be completed.

Initialization Phase

The initialization phase function void xwos_init(void) is defined by XWOS and initializes the XWOS kernel. Users must not redefine this function. xwos_init() accesses global variables, so memory initialization and data section relocation must be completed in the Pre-initialization Phase. In multi-core systems, xwos_init() is called once in each CPU’s initialization flow.

Post-initialization Phase

In the post-initialization phase, the user must provide the function definition: void xwos_postinit(void):

• The user may choose to complete driver initialization in this phase;
• The user may choose to complete dynamic memory allocator initialization in this phase;

Main Function Phase

• The user may choose to complete driver initialization in this phase;
• The user may choose to complete dynamic memory allocator initialization in this phase;
• The user must create threads in this phase;
• The user must call xwos_skd_start_lc() in this phase to start the scheduler.

User-defined Boot Flow

If the user uses a custom boot flow, xwos_init() must be called before calling any XWOS API. This function accesses global variables and must be called only after data section relocation is complete.

In multi-core systems, xwos_init() must be called once in each CPU’s initialization flow.

Custom Boot Flow Example

TODO