CC2538的sleep timer写入问题

您好，我现在想对CC2538的sleep timer写入从别的地方接收到的时间值，所用代码为：

    rtimer_clock_t cur_rt_ticks_low;

    while((REG(SMWDTHROSC_STLOAD) & SMWDTHROSC_STLOAD_STLOAD) != 1);

    INTERRUPTS_DISABLE();

    cur_rt_ticks_low = clock & 0x00000000FFFFFFFF;

    printf("clock_set_accurate_64 - %lu\n",cur_rt_ticks_low);

    /* ST0 latches ST[1:3] and must be written last */

    REG(SMWDTHROSC_ST3) = (cur_rt_ticks_low >> 24) & 0x000000FF;

    REG(SMWDTHROSC_ST2) = (cur_rt_ticks_low >> 16) & 0x000000FF;

    REG(SMWDTHROSC_ST1) = (cur_rt_ticks_low >> 8) & 0x000000FF;

    REG(SMWDTHROSC_ST0) = cur_rt_ticks_low & 0x000000FF;

    rtimer_clock_t rv;

    /* SMWDTHROSC_ST0 latches ST[1:3] and must be read first */

    rv = REG(SMWDTHROSC_ST0);

    rv |= (REG(SMWDTHROSC_ST1) << 8);

    rv |= (REG(SMWDTHROSC_ST2) << 16);

    rv |= (REG(SMWDTHROSC_ST3) << 24);

    printf("clock_set_accurate_64 - %lu\n",rv);

    INTERRUPTS_ENABLE();

写入之后马上读出，两次printf得到的结果不一样。也就是说上面4句没有能够将cur_rt_ticks_low数据写入吗？写入参考了contiki里面的rtimer_arch_schedule函数的用法，为什么还会这样？