zephyr初始化流程

1、调用应用层main()函数

        kernel/init.c      181行

/**
 *
 * @brief Mainline for kernel's background task
 *
 * This routine completes kernel initialization by invoking the remaining
 * init functions, then invokes application's main() routine.
 *
 * @return N/A
 */
static void _main(void *unused1, void *unused2, void *unused3)

2、调取_main()函数

    kernel/init.c    241行    317行

/**
 *
 * @brief Initializes kernel data structures
 *
 * This routine initializes various kernel data structures, including
 * the init and idle threads and any architecture-specific initialization.
 *
 * Note that all fields of "_kernel" are set to zero on entry, which may
 * be all the initialization many of them require.
 *
 * @return N/A
 */
static void prepare_multithreading(struct k_thread *dummy_thread)

static void switch_to_main_thread(void)

初始化内核数据结构，该函数初始化各种内核数据结构，包括init和idle线程、任意指定架构的初始化

3、调用prepare_multithreading()，switch_to_main_thread()函数

    kernel/init.c        347行

/**
 *
 * @brief Initialize kernel
 *
 * This routine is invoked when the system is ready to run C code. The
 * processor must be running in 32-bit mode, and the BSS must have been
 * cleared/zeroed.
 *
 * @return Does not return
 */
FUNC_NORETURN void _Cstart(void)

    当系统可以运行C代码试调用，处理器必须以32位模式运行，BSS必须清除或置零。

    BSS段用来存放程序中未初始化的全局变量和静态变量的内存区域，可读写，在程序运行前自动清0

4、调用_Cstart()函数

        arch/arm/core/cortex_m    prep_c.c    104行

/**
 *
 * @brief Prepare to and run C code
 *
 * This routine prepares for the execution of and runs C code.
 *
 * @return N/A
 */
void _PrepC(void)

    此函数准备执行并运行C代码

5、调用_PrepC()函数

    arch/arm/core/cortex_m/    reset.S        50行 58行

/**
 *
 * @brief Reset vector
 *
 * Ran when the system comes out of reset. The processor is in thread mode with
 * privileged level. At this point, the main stack pointer (MSP) is already
 * pointing to a valid area in SRAM.
 *
 * Locking interrupts prevents anything but NMIs and hard faults from        NMI非屏蔽中断
 * interrupting the CPU. A default NMI handler is already in place in the
 * vector table, and the boot code should not generate hard fault, or we're in
 * deep trouble.
 *
 * We want to use the process stack pointer (PSP) instead of the MSP, since the
 * MSP is to be set up to point to the one-and-only interrupt stack during later
 * boot. That would not be possible if in use for running C code.
 *
 * When these steps are completed, jump to _PrepC(), which will finish setting
 * up the system for running C code.
 *
 * @return N/A
 */
SECTION_SUBSEC_FUNC(TEXT,_reset_section,__reset)
    /*
 * The entry point is located at the __reset symbol, which
 * is fetched by a XIP image playing the role of a bootloader, which jumps to
 * it, not through the reset vector mechanism. Such bootloaders might want to
 * search for a __start symbol instead, so create that alias here.
 */
SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)