输入捕获中断是如何工作的

亲爱的各位，我在DSPIC33 E中使用IC模块作为跟随者4代码如下：在每第四个边、第二个边、第四个边、第二个边等上，用LeD3（Twitter）来中断。FoSC＝80MHZOfc= 40MHZalSOON，请某人解释IC1BUF（FIFO）。它是如何工作的。为什么我们在内部中断了2次？范围PIC：黄色是输入信号，蓝色是中断目标：测量蓝色中断之间的时间-最小频率＝0.83Hz（1200毫秒）和马克斯FRQ= 83.33赫兹（12ms）。



      以下为原文

    Dear all,
                      I use IC module in dspic33e as follows
unsigned int Capture1, Capture2;
unsigned int counts;
unsigned long timeperiod = 0;
void Hall_Capture(void)
{
TRISHALL=1;
ANSELHALL=0;
RPINR7bits.IC1R=0b0110011;
IFS0bits.IC1IF = 0; // Clear the IC1 interrupt status flag
IEC0bits.IC1IE = 1; // Enable IC1 interrupts
IPC0bits.IC1IP = 1; // Set module interrupt priority as 1
IC1CON1bits.ICSIDL = 0; // Input capture will continue to operate in CPU idle mode
IC1CON1bits.ICTSEL = 0b010; // T4 is the clock source for the IC1 module
IC1CON1bits.ICI = 0b00; // Interrupt on every capture event
IC1CON1bits.ICBNE = 0; // Input capture is empty
IC1CON1bits.ICM = 0b100; // Capture mode; every fourth rising edge (Prescaler Capture mode)
IC1CON2bits.IC32 = 0; // Cascade module operation is disabled
IC1CON2bits.ICTRIG = 0; // Input source used to synchronize the input capture timer of
// another module (Synchronization mode)
IC1CON2bits.TRIGSTAT = 0; // IC1TMR has not been triggered and is being held clear
IC1CON2bits.SYNCSEL = 0b0; // No Sync or Trigger source for the IC1 module

}
void __attribute__ ((__interrupt__, no_auto_psv)) _IC1Interrupt(void)
{

Capture1 = IC1BUF; // Read and save off first capture entry
Capture2 = IC1BUF; // Read and save off second capture entry
LED3=~LED3;
//LED3^=1;
IFS0bits.IC1IF = 0; // Reset respective interrupt flag
if(Capture1>Capture2)
Timeperiod= Capture2-Capture1;
else
Timeperiod= (TMR4-Capture1)+Capture2;
}
timer 4 code as follows
    T4CONbits.TON = 0; // Disable Timer
    T4CONbits.TCS = 0; // Select internal instruction cycle clock
    T4CONbits.TGATE = 0; // Disable Gated Timer mode
    T4CONbits.TCKPS = 0b00; // Select 1:1 Prescaler
    TMR4 = 0x00; // Clear timer register
    PR4 = 0xFFFF; /*one interrupt happens in 1 ms PR4=(1/(Fcy/8))*5000=0.001s */
    IPC6bits.T4IP = 0x01; // Set Timer4 Interrupt Priority Level
    IFS1bits.T4IF = 0; // Clear Timer4 Interrupt Flag
    IEC1bits.T4IE = 1; // Enable Timer4 interrupt
   
    T4CONbits.TON = 1; // Enable Timer4

I see interrupt on by Led3(toggle) on every 4th edge, 2nd edge,4th edge, 2nd edge and so on.
Fosc=80Mhz
Fosc=40Mhz

Also
Please, someone, explain IC1BUF (FIFO) . How it works. ? Why we read 2 times inside interrupt.?

Scope Pic: Yellow is the input signal and Blue is the interrupt
Goal: measuring the time between Blue interrupts- Min freq.=0.83hz(1200ms) and Max freq=83.33hz(12ms)