system.c

#include <stm32l433xx.h>
#include "usb.h"
#include "floppy.h"

#define nop()  __asm__ __volatile__ ("nop" ::)

void SystemInitError(uint8_t error_source) {
  while(1);
}

void SystemInit() {
  // Enable FPU
  SCB->CPACR |= 0xf00000;

  RCC->CR |= (1<<8);
  /* Wait until HSI ready */
  while ((RCC->CR & RCC_CR_HSIRDY) == 0);

  /* Disable main PLL */
  RCC->CR &= ~(RCC_CR_PLLON);
  /* Wait until PLL ready (disabled) */
  while ((RCC->CR & RCC_CR_PLLRDY) != 0);

  /* Configure Main PLL */
  RCC->PLLCFGR = (1<<24)|(10<<8)|2;

  /* PLL On */
  RCC->CR |= RCC_CR_PLLON;
  /* Wait until PLL is locked */
  while ((RCC->CR & RCC_CR_PLLRDY) == 0);

  /*
   * FLASH configuration block
   * enable instruction cache
   * enable prefetch
   * set latency to 2WS (3 CPU cycles)
   */
  FLASH->ACR |= FLASH_ACR_ICEN | FLASH_ACR_PRFTEN | FLASH_ACR_LATENCY_2WS;

  /* Set clock source to PLL */
  RCC->CFGR |= RCC_CFGR_SW_PLL;
  /* Check clock source */
  while ((RCC->CFGR & RCC_CFGR_SWS_PLL) != RCC_CFGR_SWS_PLL);

}