File content as of revision 0:9096775ac85a:

#include"HSE_Config.h"

uint8_t HSE_Config()
{
    HAL_RCC_DeInit();  // we have to reset the clock settings !
        
    RCC_OscInitTypeDef RCC_OscInitStruct;
    RCC_ClkInitTypeDef RCC_ClkInitStruct;

    /* The voltage scaling allows optimizing the power consumption when the device is
       clocked below the maximum system frequency, to update the voltage scaling value
       regarding system frequency refer to product datasheet. */
    __HAL_RCC_PWR_CLK_ENABLE();
    __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE2);

    // Enable HSE oscillator and activate PLL with HSE as source
    RCC_OscInitStruct.OscillatorType      = RCC_OSCILLATORTYPE_HSE;
    
    RCC_OscInitStruct.HSEState            = RCC_HSE_ON; // External 8 MHz xtal on OSC_IN/OSC_OUT
    RCC_OscInitStruct.PLL.PLLState        = RCC_PLL_ON;
    RCC_OscInitStruct.PLL.PLLSource       = RCC_PLLSOURCE_HSE;
    RCC_OscInitStruct.PLL.PLLM            = 8;             // VCO input clock = 1 MHz (8 MHz / 8)
    RCC_OscInitStruct.PLL.PLLN            = 336;           // VCO output clock = 336 MHz (1 MHz * 336)
    RCC_OscInitStruct.PLL.PLLP            = RCC_PLLP_DIV4; // PLLCLK = 84 MHz (336 MHz / 4)
    RCC_OscInitStruct.PLL.PLLQ            = 7;             // USB clock = 48 MHz (336 MHz / 7) --> OK for USB
    if(HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
    {
        return  0;    
    }

    // Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2 clocks dividers
    RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2;
    RCC_ClkInitStruct.SYSCLKSource   = RCC_SYSCLKSOURCE_PLLCLK; // 84 MHz
    RCC_ClkInitStruct.AHBCLKDivider  = RCC_SYSCLK_DIV1;         // 84 MHz
    RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;           // 42 MHz
    RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;           // 84 MHz
    if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK) {
        return 0; // FAIL
    }
    SystemCoreClockUpdate();
    return 1; // OK
}