#include "CH32V00xxx.h"
extern "C" void SystemInit ();
enum CLKSRC : uint32_t {
  CLK_HSI = 0u,
  CLK_HSE,
  CLK_PLL,
};

void SystemInit(void) {
  RCC.CFGR0.R   = 0u;        // prescaler OFF
  RCC.CTLR.modify([](RCC_Type::CTLR_DEF & r) -> auto {
    r.B.HSITRIM = 0x10u;
    r.B.HSION   = SET;
    r.B.HSEBYP  = SET;
    r.B.CSSON   = SET;
    r.B.PLLON   = SET;
    return r.R;
  });
  FLASH.ACTLR.B.LATENCY = SET;
  RCC.INTR.R = 0x009F0000u;   // clear interrupts
  while (RCC.CTLR.B.PLLRDY == RESET);
  RCC.CFGR0.B.SW = CLK_PLL;
  while (RCC.CFGR0.B.SWS != CLK_PLL);
}