The predivider should be 2 here.

Author: leibin

libraries/mbed/targets/cmsis/TARGET_STM/TARGET_STM32F0/TARGET_NUCLEO_F072RB/system_stm32f0xx.c

@@ -437,7 +437,7 @@ uint8_t SetSysClock_PLL_HSI(void)
   RCC_OscInitStruct.HSIState       = RCC_HSI_ON;
   RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_ON;
   RCC_OscInitStruct.PLL.PLLSource  = RCC_PLLSOURCE_HSI; // HSI div 2
-  RCC_OscInitStruct.PLL.PREDIV     = RCC_PREDIV_DIV1;
+  RCC_OscInitStruct.PLL.PREDIV     = RCC_PREDIV_DIV2;
   RCC_OscInitStruct.PLL.PLLMUL     = RCC_PLL_MUL12;
   if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK) {
       return 0; // FAIL