Re: [pyusb-users] pyusb1 picks wrong driver on Windows

[Tormod Volden]

On Thu, Aug 18, 2016 at 11:07 AM, Hermann Hamann wrote:
> 
> If it helps you:
>
> C:\Program Files\RTLSDR Scanner>dir lib*.*
> 12.04.2013 20:04 68.608 libusb-1.0.dll

Probably "C:\Program Files\RTLSDR Scanner" is in the global %PATH%, so
it is not so "private".

> < Why it crashed?
> I don't know.

I believe the crash probably happened when libusb1 accessed the device
through the libusb0.sys driver (which in theory could work but the
different drivers have their subtleties). libusb1 might have worked
better if it could access the device through the WinUSB driver. Since
the libusb-win32 library / libusb0 driver combination seems to work
you have likely encountered a bug in the libusb1/libusb0.sys
combination. It would be nice if you can file a bug and supply more
detail, if not to get the bug fixed, at least warn others about the
issue.

>  
> I want the backend that is in the registry.

pyusb by default looks for libusb1 first, using the path, like how
most applications loads DLLs. If you have the libusb1 DLL installed in
the path but don't want to have it selected, you must select backend
explicitly.

I suppose libusb1 (somewhere through the Windows API layers) uses the
registry to know which driver to use. It is however not obvious how
pyusb should interpret the registry to choose its backend library.
Flexibility comes at a cost.

For instance, libusb-win32 ships both a library (DLL) and a driver
(SYS) and the former always uses the latter to access the device,
whereas libusb1 is just a library and can use various drivers (WinUSB,
HID, libusb0.sys, libusbK) to access the device. The Windows driver
registry will point to which driver is in charge of a device, and the
application must perform requests to this driver, but the application
(or developer) must itself select its libraries. And the pyusb
application currently uses a DLL search to select default library
backend, regardless of the device.

If libusb1 would only support WinUSB, and we had a strict
driver<->libusb relation, heuristics based on the registered driver
could make more sense. Add more possible backends and drivers, try to
make things consistent across platforms, and it all becomes more
complex.

Hermann, in your case you are probably better off selecting the
libusb0 backend in your python application, if you know that your
device requires libusb0.sys. Otherwise, register the device for WinUSB
(with .inf file or Zadig), make sure a known good libusb1.dll is
installed in the path (before any third party libusb1.dll) and select
the libusb1 backend in your python application for good measure.

BTW, Hermann's example patch hardcodes "ControlSet002" which I believe
should be "CurrentControlSet", unless there are better ways to find
the "Service" associated with a device. I also think device instances
(e.g. different serial numbers but same vid/pid) can have different
Service values, and I am not sure how the patch deals with that.

Regards,
Tormod

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Re: [pyusb-users] pyusb1 picks wrong driver on Windows

[Xiaofan Chen]

On Thu, Aug 18, 2016 at 7:57 PM, Xiaofan Chen  wrote:
> On Thu, Aug 18, 2016 at 5:07 PM, Hermann Hamann  wrote:
>>
>> Hi
>>
>> > I have read so in the internet. I will post reference later.
>>
>> >
>> If it helps you:
>>
>> C:\Program Files\RTLSDR Scanner>dir lib*.*
>> Volume in Laufwerk C: hat keine Bezeichnung.
>> Volumeseriennummer: ECEC-C891
>>
>> Verzeichnis von C:\Program Files\RTLSDR Scanner
>>
>> 12.04.2013 20:04 68.608 libusb-1.0.dll
>> 1 Datei(en), 68.608 Bytes
>> 0 Verzeichnis(se), 70.811.631.616 Bytes frei
>>
>> C:\Program Files\RTLSDR Scanner>
>
> This again has nothing to do with libusb or pyusb.

I mean why your program finds this very old version of
libusb Windows dll? You probably want to use the latest
version of libusb Windows release and put the dll in the
right directory.

>> < Why it crashed?
>> I don't know.
>
> You need to figure that out.
>
>> > >
>> I want the backend that is in the registry.
>
> The registry thingy has nothing to do with your problem.
>



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Re: [pyusb-users] pyusb1 picks wrong driver on Windows

[Xiaofan Chen]

On Thu, Aug 18, 2016 at 5:07 PM, Hermann Hamann  wrote:
>
> Hi
>
>  I have read so in the internet. I will post reference later.
>
> 
> If it helps you:
>
> C:\Program Files\RTLSDR Scanner>dir lib*.*
> Volume in Laufwerk C: hat keine Bezeichnung.
> Volumeseriennummer: ECEC-C891
>
> Verzeichnis von C:\Program Files\RTLSDR Scanner
>
> 12.04.2013 20:04 68.608 libusb-1.0.dll
> 1 Datei(en), 68.608 Bytes
> 0 Verzeichnis(se), 70.811.631.616 Bytes frei
>
> C:\Program Files\RTLSDR Scanner>

This again has nothing to do with libusb or pyusb.

> < Why it crashed?
> I don't know.

You need to figure that out.

>  
> I want the backend that is in the registry.

The registry thingy has nothing to do with your problem.


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Re: [pyusb-users] pyusb1 picks wrong driver on Windows. Asking for help

[Hermann Hamann]

Hi Chris,



Yes.

 

Re: [pyusb-users] pyusb1 picks wrong driver on Windows

[Hermann Hamann]

 
Hi



I have read so in the internet. I will post reference later.




If it helps you:


C:\Program Files\RTLSDR Scanner>dir lib*.*
Volume in Laufwerk C: hat keine Bezeichnung.
Volumeseriennummer: ECEC-C891

Verzeichnis von C:\Program Files\RTLSDR Scanner

12.04.2013 20:04 68.608 libusb-1.0.dll
1 Datei(en), 68.608 Bytes
0 Verzeichnis(se), 70.811.631.616 Bytes frei

C:\Program Files\RTLSDR Scanner>

< Why it crashed?

I don't know.





I want the backend that is in the registry.

Sincerely H. H.




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