好的。我想到了。 transfer.flags 需要是一个字节而不是一个整数。傻我。现在我从 ioctl 得到一个错误代码，errno 16，我认为这意味着设备正忙。真是个工作狂。我在 libusb 邮件列表上询问过。
以下是我目前所拥有的。这真的不是那么多代码。其中大部分是 libusb 的 ctypes 结构。向下滚动到底部以查看发生错误的实际代码。
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
请您参考如下方法:
- 您是否检查过以确保
libusb_alloc_transfer和libusb_open_device_with_vid_pid的返回值有效？ - 您是否尝试过使用适当的 argtypes 注释库函数？ ？
- 您可能会遇到
transfer[0].callback = LIBUSB_TRANSFER_CB_FN(callback)的问题——您没有保留对从返回的，因此该对象可能会被释放和覆盖。CFunctionType对象的任何引用code>LIBUSB_TRANSFER_CB_FN()
下一步，我想，是安装带有调试符号的 libusb 版本，启动 GDB，在 libusb_submit_transfer() 设置断点，确保传入的 libusb_transfer 是正常的，看看是什么触发了返回的错误。
