SPI主站每隔一个字节丢失一次

我已经建立了两个PIC32，一个作为主人，一个作为奴隶。主机每秒发送一个命令字节，从一个字节回复一个字节。但是，主机只读取每秒字节。查看范围，每个主事务之间看起来有8个时钟周期。丢失的字节是奴隶在这些空白期间发送的字节。为什么会发生这样的事情？初始化：命令在定时器内发送。LATA是SS线，SPI接收中断。如果缓冲区未满，则中断设置为触发。



      以下为原文

    I've set up two PIC32s, one as a master, one as a slave. The master sends a command byte once a second, and the slave replies with a series of bytes. However, the master is only reading every second byte. Looking at the scope, there looks to be 8 clock cycles between every master transaction. The bytes being lost are the ones that the slave sends during these blanks.
Any ideas why this is happening?

Initialization:
SYSKEY=0xAA996655;
    SYSKEY=0x556699AA;
    CFGCONbits.IOLOCK = 0; //Unlock PPS
   
    SDI1R = 0b0011; //Set RB11 to SDI1
    SS1R = 0b0000; //Set RA0 to SS1
    RPB13R = 0b0011; //Set SDO1 to RB13
   
    CFGCONbits.IOLOCK = 1;
    SYSKEY=0x0; //Lock PPS
            
    SPI1CONbits.ON = 0; //off for initialisation
   
    SPI1BRG = 3; //1MHz
   
    SPI1STATbits.SPIROV = 0;
   
    SPI1CONbits.MSTEN = 1;
    SPI1CONbits.FRMEN = 1; //Framed SPI
    SPI1CONbits.FRMSYNC = 0; //SS output - master
    SPI1CONbits.FRMPOL = 1; //SS active low
    SPI1CONbits.MSSEN = 1; //SS enable
    SPI1CONbits.FRMSYPW = 1; //SS one character wide
    SPI1CONbits.FRMCNT = 0b000; //Frame pulse counter - 1pulse per character ???????????
    SPI1CONbits.MCLKSEL = 0; //Use PBCLK for Baud rate gen
    SPI1CONbits.SPIFE = 0; //SS precedes first bit clocked ??????
    SPI1CONbits.ENHBUF = 1; //Enhanced buffer mode ??????
    SPI1CONbits.SIDL = 0; //Don't stop in idle mode
    SPI1CONbits.DISSDO = 0;
    SPI1CONbits.MODE16 = 0;
    SPI1CONbits.MODE32 = 0;
    SPI1CONbits.SMP = 1; //Input data sampled at end of data output time
    SPI1CONbits.CKE = 0;
    SPI1CONbits.CKP = 1; //Clock idle high, active low
    SPI1CONbits.DISSDI = 0;
    SPI1CONbits.STXISEL = 0b00;
    SPI1CONbits.SRXISEL = 0b01; //Interrupt when receive buffer is not empty

    SPI1CON2bits.SPISGNEXT = 0; //RX FIFO not sign extended
    SPI1CON2bits.FRMERREN = 0; //no error interrupt for frame error
    SPI1CON2bits.SPIROVEN = 0; //Receive overflow does not generate error events
    SPI1CON2bits.SPITUREN = 0; //Transmit Underrun Does Not Generates Error Events
    SPI1CON2bits.IGNROV = 1; //A ROV is not a critical error; during ROV data in the fifo is not overwritten by receive data
    SPI1CON2bits.IGNTUR = 1; //A TUR is not a critical error and zeros are transmitted until the SPIxTXB is not empty
    SPI1CON2bits.AUDEN = 0; //Audio disabled
   
    IPC7bits.SPI1IP = 6;
    IEC1bits.SPI1TXIE = 0;
    IFS1bits.SPI1TXIF = 0;
    IEC1bits.SPI1RXIE = 1;
    IFS1bits.SPI1RXIF = 0;
    IEC1bits.SPI1EIE = 1;
    IFS1bits.SPI1EIF = 0;
   
    LATAbits.LATA0 = 1;
   
    SPI1CONbits.ON = 1;

The command is sent inside a timer. LATA is the SS line.
SPI1BUF = 0x96;
LATAbits.LATA0 = 0;

The SPI receive interrupt. The interrupt is set to fire if the buffer is not full.
static uint8_t Counter = 0;
void __ISR(_SPI_1_VECTOR, ipl6AUTO) _IntHandlerSPIInstance0(void)
{
    if (IFS1bits.SPI1RXIF == 1)
    {
        
        if (Counter >= 8)
        {
            Counter = 0;
            LATAbits.LATA0 = 1;
        }
        else
        {
            appData.RXlist[Counter] = SPI1BUF;
            Counter++;
            SPI1BUF = 0x0F;
        }
        
        SPI1STATbits.SPIROV = 0;
        IFS1bits.SPI1RXIF = 0;
    }
}