求问这段代码的解释
```c
#define AD_LEN 200
u16 arry_ph_tip,arry_ph_ad[AD_LEN],arry_average_ph;
void TIM3_IRQHandler(void)
{
static u8 tip;
if (TIM_GetITStatus(TIM3, TIM_IT_Update) != RESET)
{
arry_ph_tip=(arry_ph_tip+1)%AD_LEN;
arry_ph_ad[arry_ph_tip]=vad_get();
if(arry_ph_tip>=(AD_LEN-1))
{
arry_average_ph=vAverage(arry_ph_ad,AD_LEN);
vddl_get_ph(((float)arry_average_ph*3250.f/4095.f-1780.0)/2.0);//3260 ad的Vref
}
TIM_ClearITPendingBit(TIM3, TIM_IT_Update );
}
}
```