+# define STM_RCC_CFGR_MCO_RC 1
+# define STM_RCC_CFGR_MCO_LSI 2
+# define STM_RCC_CFGR_MCO_LSE 3
+# define STM_RCC_CFGR_MCO_SYSCLK 4
+# define STM_RCC_CFGR_MCO_HSI 5
+# define STM_RCC_CFGR_MCO_HSE 6
+# define STM_RCC_CFGR_MCO_PLLCLK 7
+# define STM_RCC_CFGR_MCO_HSI48 8
+# define STM_RCC_CFGR_MCO_MASK (0xf)