CC2640的SCLK_HF如何切换到XOSC

hi，我切换的流程是

    AON_WUC->AUXCTL |= (1 << 0);
    while(0 == (AON_WUC->PWRSTAT & (1 << 5)));
    AUX_WUC->MODCLKEN0 |= (1 << 6);     // MUST enable clock for AUX_DDI0_OSC,or AUX_DDI0_OSC can't rw
    AUX_DDI0_OSC->CTL0 |= (1 << 0); // set SCLK_HF to XOSC
    while((AUX_DDI0_OSC->STAT0 & (1 << 0)));
    AUX_DDI0_OSC->CTL0 |= (1 << 16); // switch it
    while(AUX_DDI0_OSC->STAT0 & (1 << 0));

但是执行完这些后DDI_0_OSC:STAT0:SCLK_HF_SRC依然是RCOSC，无法切换到XOSC，请问还有哪个步骤有问题？