32 bits data transfer from Pi to FPGA using spidev

I'm trying to 32 bits data send and receive between Pi and FPGA using spi. So, I set the Pi as master and FPGA as slave. And use xfer2 function from spidev. But, I couldn't read data. How can I fix it?.

First 4 bytes for deciding read or write cycle. And last 4 bytes are the data to transfer to FPGA. For example, if the first 4 bytes are 0x00000000, then this is write cycle. And, last 4 bytes are transferred to FPGA. So, I want to send data by using xfer2. like this, xfer2([0x00000000, 0x000000ff]). But, it didn't work. So, I thought that xfer2 only transfer data 1-byte per. And, I changed it to xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff]).

And, whatever data I sent, this code just printed out [0, 0, 0, 0, 0, 0, 0, 0].

My simple spi test code is below.

import spidev
import time

spi=spidev.SpiDev()
spi.open(0,1)
spi.max_speed_hz= 190000000 

while True:

    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff]) # write
    time.sleep(0.1)

    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01]) # write
    time.sleep(0.1)

    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read  
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x20]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40]) # write
    time.sleep(0.1)
    
    resp = spi.xfer2([0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]) # read
    print(resp)
    time.sleep(0.1)
    resp1 = spi.xfer2([0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80]) # write
    time.sleep(0.1)

This is the results

enter image description here