USB2ANY: When trying to output the serial number of the device, it outputs a negative number

Use ctypes.c_buffer() or ctypes.create_string_buffer(), instead of a ctypes.c_long() reference, to get the serial number.

Excerpt below is from an internal library (U2A_ERRWrapper uses __getattr__ to apply a wrapper function that checks for negative status code from API calls, and raises readable errors):

class USB2ANY:
    u2adll = U2A_ERRWrapper(ctypes.WinDLL(_DLL_PATH))
    
    @classmethod
    def _FindControllers(cls) -> int:
        '''
        Scan the USB, and return the total number of USB2ANY found.
        '''
        return cls.u2adll.u2aFindControllers()

    @classmethod
    def _GetSerialNumber(cls, index: int) -> ctypes.c_buffer:
        '''
        Returns a ctypes.c_buffer containing the ascii bytes corresponding to 
        the serial number of a USB2ANY at the given index, with respect to 
        the ordering determined by _FindControllers function.
        '''
        buf = ctypes.c_buffer(40) # `40` is from SERNUM_LEN in USB2ANY_SDK.h
        status = cls.u2adll.u2aGetSerialNumber(index, buf)
        return buf

    @classmethod
    def Controllers(cls) -> List[ctypes.c_buffer]:
        '''
        Returns a list of ctypes.c_buffers containing the serial numbers of 
        all detected USB2ANY.
        '''
        return [cls._GetSerialNumber(i)
                for i in range(cls._FindControllers())]

    def Open(self, controller: Optional[ctypes.c_buffer] = None) -> None:
        '''
        Acquires a handle to the controller specified by the serial number. 
        If controller argument is omitted, the handle will be acquired for 
        the first USB2ANY enumerated.
    
        On failure, the handle is not assigned, and an exception is raised.
        '''
        if controller is None: # use an empty buffer to select first U2A
            controller = ctypes.c_buffer(0)
        self._handle = self.u2adll.u2aOpen(controller)

There's a lot of I2C functions, and the explanations in the API manual aren't great. A more thorough explanation of the transaction functions can be found here: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1389829/usb2any-multibyte-i2c-transactions

Note that if your application doesn't have pull-up resistors on the I2C bus, you may need to enable the USB2ANY's on-board pull-ups, which requires enabling the 3.3V power supply (u2aPower_Enable(HANDLE, 1, 2, 2)).