请教T113运行主频的设置问题

[L13819506056]

使用芒果派小麻雀板的T113做测试，CPU运行主频高于800MHz，切换时就跑飞。测试代码如下，请求大佬们支招：

#define CPU_RUN_FREQ           1200000000 
#define SYS_XTOSC_CLK            24000000 
static void set_pll_cpux_axi(void)
{
		uint32_t val;
	
  int n =  (CPU_RUN_FREQ / SYS_XTOSC_CLK -1 ) & 0xFF;

  
	/* Switch to PLL_PERI(1X) clock while changing cpu pll (600MHz) */
	CCU_CPU_AXI_CFG  =  (4<<24)  ;
  sdelay(10000);
	/*  cpu pll rate = 24000000 * n      */
  val = PLL_CPU_CTRL_REG & (~((0xff << 8) | (1 << 27)));
 	val |= (n << 8);
	
	PLL_CPU_CTRL_REG  = val;
	PLL_CPU_CTRL_REG &= ~(1 << 29);
  sdelay(5);
  PLL_CPU_CTRL_REG |= (1 << 29);
  sdelay(1000);
  while( (PLL_CPU_CTRL_REG &(1 << 28)) == 0 );  /* wait for pll lock */
  PLL_CPU_CTRL_REG |= (1 << 27);                 /* open pll out gate */
  sdelay(10000);

/* Switch clock source */  
	CCU_CPU_AXI_CFG  =    (3 << 24);
  sdelay(10000);
                           
}

这一句CCU_CPU_AXI_CFG = (3 << 24)一执行，CPU就跑飞了.
请求支援。期待中。