/*----------------------------------------------------------------------------
* Name: B.c
* Purpose: LED Flasher
*----------------------------------------------------------------------------
* This file is part of the uVision/ARM development tools.
* This software may only be used under the terms of a valid, current,
* end user licence from KEIL for a compatible version of KEIL software
* development tools. Nothing else gives you the right to use this software.
*
* This software is supplied "AS IS" without warranties of any kind.
*
* Copyright (c) 2016 Keil - An ARM Company. All rights reserved.
*----------------------------------------------------------------------------*/

#include <stdio.h>

#include "stm32l4xx.h"                // Device header

uint32_t red_led = 0;
uint32_t green_led = 0;

volatile uint32_t msTicks;                         /* counts 1ms timeTicks */

/*----------------------------------------------------------------------------
* SysTick_Handler:
*----------------------------------------------------------------------------*/

void SysTick_Handler(void) {
msTicks++;
}

/*----------------------------------------------------------------------------
* Delay: delays a number of Systicks0
*----------------------------------------------------------------------------*/
void Delay (uint32_t dlyTicks) {
uint32_t curTicks;

curTicks = msTicks;
while ((msTicks - curTicks) < dlyTicks) { __NOP(); }
}

/*----------------------------------------------------------------------------
* SystemCoreClockConfigure: configure SystemCoreClock using HSI

*----------------------------------------------------------------------------*/
void SystemCoreClockConfigure(void) {

RCC->CR |= ((uint32_t)RCC_CR_HSION);                   /* Enable HSI */
while ((RCC->CR & RCC_CR_HSIRDY) == 0);                /* Wait for HSI Ready */

RCC->CFGR = RCC_CFGR_SW_HSI;                         /* HSI is system clock */
while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_HSI); /* Wait for HSI used as system clock */

FLASH->ACR = (FLASH_ACR_PRFTEN |                /* Enable Prefetch Buffer */
            FLASH_ACR_ICEN    |                /* Instruction cache enable */
            FLASH_ACR_DCEN    |                /* Data cache enable */
            FLASH_ACR_LATENCY_4WS );                /* Flash 4 wait state */

RCC->CFGR |= (RCC_CFGR_HPRE_DIV1 |                   /* HCLK = SYSCLK */
            RCC_CFGR_PPRE1_DIV2 |                   /* APB1 = HCLK/2 */
            RCC_CFGR_PPRE2_DIV1 );                /* APB2 = HCLK/1 */

RCC->CR &= ~RCC_CR_PLLON;                            /* Disable PLL */

A load connected in star is supplied from a 400V 3 phase system and...