I have this python code:

import ctypes
lib = ctypes.CDLL('/home/pi/serial_communication/crc.so')

C=0
def spi_process(gpio,level,tick):
    print("Detected")
    data = [0]*1024
    with open(output_file_path(), 'w') as f:
        for x in range(1):
            spi.xfer2(data)
            values = struct.unpack("<"  "I"*256, bytes(data))
            C = lib.crc32Word(0xffffffff,data,1024)
            f.write("\n")
            f.write("\n".join([str(x) for x in values]))
        print(C)

input("Press Enter to start the process ")

cb1=pi.callback(INTERRUPT_GPIO, pigpio.RISING_EDGE, spi_process)

while True:
    lib.crc32Word.restype=ctypes.c_int
    lib.crc32Word.argtypes=[ctypes.c_int, ctypes.POINTER(ctypes.c_void_p), ctypes.c_int]
    time.sleep(1)

But when I run it, I receive this error:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.7/threading.py", line 917, in _bootstrap_innerself.run()
  File "/usr/lib/python3/dist-packages/pigpio.py", line 1213, in run cb.func(cb.gpio, newLevel, tick)
  File "2crc_spi.py", line 47, in spi_process
    C=lib.crc32Word(0xffffffff,data,1024)
ctypes.ArgumentError: argument 2: <class 'TypeError'>: LP_c_long instance instead of list 

I am trying to call this C function from a c library:

uint32_t crc32Word(uint32_t crc, const void *buffer, uint32_t size)

Can someone please help? Thanks.

CodePudding user response：

The problem can be reduced to the following code. The 2nd parameter was incorrect as ctypes.POINTER(ctypes.c_void_p) would be used for C void** not void*. The other parameters were using signed vs. unsigned types so that has been corrected as well. The data must be either bytes or a ctypes array such as (c_uint8 * 1024)() to be suitable for c_void_p.

lib = ctypes.CDLL('/home/pi/serial_communication/crc.so')
lib.crc32Word.argtypes = ctypes.c_uint32, ctypes.c_void_p, ctypes.c_uint32
lib.crc32Word.restype = ctypes.c_uint32

data = bytes([0] * 1024)
crc = lib.crc32Word(0xffffffff, data, len(data))