+ ao_arch_nop();
+
+ stm_rcc.cfgr = (stm_rcc.cfgr & ~(STM_RCC_CFGR_SW_MASK << STM_RCC_CFGR_SW)) |
+ (STM_RCC_CFGR_SW_MSI << STM_RCC_CFGR_SW);
+
+ /* wait for system to switch to MSI */
+ while ((stm_rcc.cfgr & (STM_RCC_CFGR_SWS_MASK << STM_RCC_CFGR_SWS)) !=
+ (STM_RCC_CFGR_SWS_MSI << STM_RCC_CFGR_SWS))
+ ao_arch_nop();