Currently,I think the key point is how to pass the correct memory address to
the libusb, is there any other method beyond :
buffer = array.array('B','\x00' * 255)
address, length = buffer.buffer_info()
or....there is an bug in libusb,but I can not figure out....
2010/9/10 Wander Lairson <wander.lair...@gmail.com>
> > Hello wander.lairson:
> > First of all,thanks for your contribution for
> the opensource community
> > and the work for libusb, I appricate it very much.
> > Currently I want to fetch the serial number of the massive storage
> > device,which need the string descriptor. Unfortunately,the python
> interface
> > hasn't wrapped the API yet. I tried to implement it myself and copy some
> of
> > the __read function code. Like this:
> >>
> >> def get_string_descriptor_ascii(self,dev_handle,desc_index):
> >>
> >> """Added by GaoHong"""
> >>
> >> buffer = array.array('B','\x00' * 255)
> >>
> >> address, length = buffer.buffer_info()
> >>
> >>
> >>
>
> _check(_lib.libusb_get_string_descriptor_ascii(dev_handle,desc_index,cast(address,
> >> POINTER(c_ubyte)),length))
>
> I am not sure if it is the problem (because I don't know how ctypes
> pushes arguments in the stack), but if you haven't supplied the
> function prototype, desc_index will be treated as an integer instead
> of a 8 bits variable (as in the libusb_get_string_descriptor_ascii
> interface). You might try this to see if it is a problem:
>
>
> _check(_lib.libusb_get_string_descriptor_ascii(dev_handle,c_uint8(desc_index),cast(address,POINTER(c_ubyte)),length))
>
> If not, I am affraid you will have to play with WinDBG to see what's
> going on. Also, try to write a little C program that call
> libusb_get_string_descriptor_ascii. I may cut off the possiblity of a
> bug in libusb.
>
> PS: I could debug it for you, but currently I do have no free time for
> it, I am really sorry.
>
> >>
> >> return data
> >
> > but the result always raise WindowsError: exception: access violation
> > reading 0x00000010
> > File "E:\my_doc\My Dev\python\GWP 0902\usb_finder.py", line 60, in
> <module>
> > print
> >
> 'Manufacturer:',back.get_string_descriptor_ascii(dev._ctx.handle,dev.iManufacturer)
> > File "D:\Python26\Lib\site-packages\usb\_debug.py", line 53, in do_trace
> > return f(*args, **named_args)
> > File "D:\Python26\Lib\site-packages\usb\backend\libusb10.py", line 593,
> in
> > get_string_descriptor_ascii
> >
>
> _check(_lib.libusb_get_string_descriptor_ascii(dev_handle,desc_index,cast(address,
> > POINTER(c_ubyte)),length-1))
> > I don't know why,the only difference from __read function:
> >>
> >> def __read(self, fn, dev_handle, ep, intf, size, timeout):
> >>
> >> buffer = array.array('B', '\x00' * size)
> >>
> >> address, length = buffer.buffer_info()
> >>
> >> transferred = c_int()
> >>
> >> _check(fn(dev_handle,
> >>
> >> ep,
> >>
> >> cast(address, POINTER(c_ubyte)),
> >>
> >> length,
> >>
> >> byref(transferred),
> >>
> >> timeout))
> >>
> >> return buffer[:transferred.value]
> >
> > is the called function.
> > Can you tell me why? Thank you very much.
> > --
> > It's a long journey to go! :-)
> > Legend since 1985...
> >
>
>
>
> --
> Best Regards,
> Wander Lairson Costa
>
--
It's a long journey to go! :-)
Legend since 1985...
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