请教：rt_hw_stack_init()函数

rt_uint8_t *rt_hw_stack_init(void *tentry, void *parameter,
                             rt_uint8_t *stack_addr, void *texit)
{
    struct stack_frame * stack_frame;
    rt_uint8_t * stk;
    unsigned long i;
    stk = stack_addr + sizeof(rt_uint32_t);
    stk -= sizeof(struct stack_frame);
    stack_frame = (struct stack_frame *)stk;
    /* init all register */
    for(i=0; i<sizeof(struct stack_frame)/sizeof(rt_uint32_t); i++)
    {
        ((rt_uint32_t*)stack_frame)[i] = 0xdeadbeef;
    }
    stack_frame->exception_stack_frame.r0 = (unsigned long)parameter; /* r0 : argument */
    stack_frame->exception_stack_frame.r1 = 0;                        /* r1 */
    stack_frame->exception_stack_frame.r2 = 0;                        /* r2 */
    stack_frame->exception_stack_frame.r3 = 0;                        /* r3 */
    stack_frame->exception_stack_frame.r12 = 0;                       /* r12 */
    stack_frame->exception_stack_frame.lr = (unsigned long)texit;     /* lr */
    stack_frame->exception_stack_frame.pc = (unsigned long)tentry;    /* entry point, pc */
    stack_frame->exception_stack_frame.psr = 0x01000000L;             /* PSR */
    /* return task's current stack address */
    return stk;
}

thread->sp = (void *)rt_hw_stack_init(thread->entry, thread->parameter,
        (void *) ((char *)thread->stack_addr + thread->stack_size - 4),
        (void *)rt_thread_exit);

    stk  = (rt_uint8_t *)RT_ALIGN_DOWN((rt_uint32_t)stk, 8);