帮助理解使用libusb-1.0和ctypes的异步USB操作

Question

好的，我搞明白了。transfer.flags 需要是一个字节，而不是一个整数。真是我太傻了。现在我从 ioctl 得到了一个错误代码，errno 16，我觉得这意味着设备正在忙。真是个工作狂。我已经在 libusb 的邮件列表上询问了。

下面是我目前的进展。其实代码不多。大部分都是 libusb 的 ctypes 结构。往下滚动到最底部可以看到出错的实际代码。

from ctypes import *

VENDOR_ID = 0x04d8
PRODUCT_ID = 0xc002
_USBLCD_MAX_DATA_LEN = 24
LIBUSB_ENDPOINT_IN = 0x80
LIBUSB_ENDPOINT_OUT = 0x00

class EnumerationType(type(c_uint)):  
    def __new__(metacls, name, bases, dict):  
        if not "_members_" in dict:  
            _members_ = {}  
            for key,value in dict.items():  
                if not key.startswith("_"):  
                    _members_[key] = value  
            dict["_members_"] = _members_  
        cls = type(c_uint).__new__(metacls, name, bases, dict)  
        for key,value in cls._members_.items():  
            globals()[key] = value  
        return cls  

    def __contains__(self, value):
        return value in self._members_.values()

    def __repr__(self):
        return "<Enumeration %s>" % self.__name__

class Enumeration(c_uint):
    __metaclass__ = EnumerationType
    _members_ = {}
    def __init__(self, value):
        for k,v in self._members_.items():
            if v == value:
                self.name = k
                break
        else:
            raise ValueError("No enumeration member with value %r" % value)
        c_uint.__init__(self, value)


    @classmethod
    def from_param(cls, param):
        if isinstance(param, Enumeration):
            if param.__class__ != cls:
                raise ValueError("Cannot mix enumeration members")
            else:
                return param
        else:
            return cls(param)

    def __repr__(self):
        return "<member %s=%d of %r>" % (self.name, self.value, self.__class__)


class LIBUSB_TRANSFER_STATUS(Enumeration):
    _members_ = {'LIBUSB_TRANSFER_COMPLETED':0,
            'LIBUSB_TRANSFER_ERROR':1,
            'LIBUSB_TRANSFER_TIMED_OUT':2,
            'LIBUSB_TRANSFER_CANCELLED':3,
            'LIBUSB_TRANSFER_STALL':4,
            'LIBUSB_TRANSFER_NO_DEVICE':5,
            'LIBUSB_TRANSFER_OVERFLOW':6}

class LIBUSB_TRANSFER_FLAGS(Enumeration):
    _members_ = {'LIBUSB_TRANSFER_SHORT_NOT_OK':1<<0,
            'LIBUSB_TRANSFER_FREE_BUFFER':1<<1,
            'LIBUSB_TRANSFER_FREE_TRANSFER':1<<2}

class LIBUSB_TRANSFER_TYPE(Enumeration):
    _members_ = {'LIBUSB_TRANSFER_TYPE_CONTROL':0,
            'LIBUSB_TRANSFER_TYPE_ISOCHRONOUS':1,
            'LIBUSB_TRANSFER_TYPE_BULK':2,
            'LIBUSB_TRANSFER_TYPE_INTERRUPT':3}

class LIBUSB_CONTEXT(Structure):
    pass

class LIBUSB_DEVICE(Structure):
    pass

class LIBUSB_DEVICE_HANDLE(Structure):
    pass

class LIBUSB_CONTROL_SETUP(Structure):
    _fields_ = [("bmRequestType", c_int),
            ("bRequest", c_int),
            ("wValue", c_int),
            ("wIndex", c_int),
            ("wLength", c_int)]

class LIBUSB_ISO_PACKET_DESCRIPTOR(Structure):
    _fields_ = [("length", c_int),
            ("actual_length", c_int),
            ("status", LIBUSB_TRANSFER_STATUS)]

class LIBUSB_TRANSFER(Structure):
    pass

LIBUSB_TRANSFER_CB_FN = CFUNCTYPE(c_void_p, POINTER(LIBUSB_TRANSFER))

LIBUSB_TRANSFER._fields_ = [("dev_handle", POINTER(LIBUSB_DEVICE_HANDLE)),
            ("flags", c_ubyte),
            ("endpoint", c_ubyte),
            ("type", c_ubyte),
            ("timeout", c_uint),
            ("status", LIBUSB_TRANSFER_STATUS),
            ("length", c_int),
            ("actual_length", c_int),
            ("callback", LIBUSB_TRANSFER_CB_FN),
            ("user_data", c_void_p),
            ("buffer", POINTER(c_ubyte)),
            ("num_iso_packets", c_int),
            ("iso_packet_desc", POINTER(LIBUSB_ISO_PACKET_DESCRIPTOR))]


class TIMEVAL(Structure):
    _fields_ = [('tv_sec', c_long), ('tv_usec', c_long)]

lib = cdll.LoadLibrary("libusb-1.0.so")
lib.libusb_open_device_with_vid_pid.restype = POINTER(LIBUSB_DEVICE_HANDLE)
lib.libusb_alloc_transfer.restype = POINTER(LIBUSB_TRANSFER)

def libusb_fill_interrupt_transfer(transfer, dev_handle, endpoint, buffer, length, callback, user_data, timeout):
    transfer[0].dev_handle = dev_handle
    transfer[0].endpoint = chr(endpoint)
    transfer[0].type = chr(LIBUSB_TRANSFER_TYPE_INTERRUPT)
    transfer[0].timeout = timeout
    transfer[0].buffer = buffer
    transfer[0].length = length
    transfer[0].user_data = user_data
    transfer[0].callback = LIBUSB_TRANSFER_CB_FN(callback)

def cb_transfer(transfer):
    print "Transfer status %d" % transfer.status

if __name__ == "__main__":
    context = POINTER(LIBUSB_CONTEXT)()
    lib.libusb_init(None)
    transfer = lib.libusb_alloc_transfer(0)
    handle = lib.libusb_open_device_with_vid_pid(None, VENDOR_ID, PRODUCT_ID)
    size = _USBLCD_MAX_DATA_LEN
    buffer = c_char_p(size)
    libusb_fill_interrupt_transfer(transfer, handle, LIBUSB_ENDPOINT_IN + 1, buffer, size, cb_transfer, None, 0)

    r = lib.libusb_submit_transfer(transfer) # This is returning -2, should be => 0.
    if r < 0:
        print "libusb_submit_transfer failed", r

    while r >= 0:
        print "Poll before"
        tv = TIMEVAL(1, 0)
        r = lib.libusb_handle_events_timeout(None, byref(tv))
        print "Poll after", r

错误处理异步编程 ctypes 设备通信 libusb usb操作

帮助理解使用libusb-1.0和ctypes的异步USB操作

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