Here’s a working example. It looks like you are passing the wrong type to the function.
Test DLL Code (“cl /W4 /LD x.c” on Windows)
#include <stdio.h>
#define SMBUS_API __declspec(dllexport)
#define SMB_MAX_DATA_SIZE 5
typedef void* SMBUS_HANDLE;
typedef struct _SMB_REQUEST
{
unsigned char Address;
unsigned char Command;
unsigned char BlockLength;
unsigned char Data[SMB_MAX_DATA_SIZE];
} SMB_REQUEST;
SMBUS_API int SmBusReadByte(SMBUS_HANDLE handle,SMB_REQUEST *request)
{
unsigned char i;
for(i = 0; i < request->BlockLength; i++)
request->Data[i] = i;
return request->BlockLength;
}
SMBUS_API SMBUS_HANDLE OpenSmbus(void)
{
return (void*)0x12345678;
}
Python code
from ctypes import *
SMB_MAX_DATA_SIZE = 5
ARRAY5 = c_ubyte * SMB_MAX_DATA_SIZE
class SMB_REQUEST(Structure):
_fields_ = [
("Address", c_ubyte),
("Command", c_ubyte),
("BlockLength", c_ubyte),
("Data", ARRAY5)]
smbus_read_byte = CDLL('x').SmBusReadByte
smbus_read_byte.argtypes = [c_void_p,POINTER(SMB_REQUEST)]
smbus_read_byte.restype = c_int
open_smbus = CDLL('x').OpenSmbus
open_smbus.argtypes = []
open_smbus.restype = c_void_p
handle = open_smbus()
print 'handle = %08Xh' % handle
smb_request = SMB_REQUEST(1,2,5)
print 'returned =',smbus_read_byte(handle,byref(smb_request))
print 'Address=",smb_request.Address
print "Command =',smb_request.Command
print 'BlockLength=",smb_request.BlockLength
for i,b in enumerate(smb_request.Data):
print "Data[%d] = %02Xh' % (i,b)
Output
handle = 12345678h
returned = 5
Address = 1
Command = 2
BlockLength = 5
Data[0] = 00h
Data[1] = 01h
Data[2] = 02h
Data[3] = 03h
Data[4] = 04h