Re: [libusb] Timeouts then Access Denied Errors on Win 7

[Richard B. <ra...@lu...>]

The logs are fairly confusing to me.  There are many, many calls to
libusb_init and libusb_exit.  Is that in your code, or is that part of
pyusb?

>
> From what I see, you do a read of 64 bytes at line 433, and you must have
> specified a 16ms timeout.  That timer expires on line 438 and gets returned
> to you on 449.  You then submit another read of 64 bytes on line 451,
> apparently with a 0ms timeout.  So why does the error message on line 469
> say the timeout was in an attempt to write?  I don't see the first write
> until line 473.
>
> It looks like you're opening three different devices.  Is that true?  Are
> you sure it's going to respond in 16ms?
>

I'm not sure about those calls to libusb_init and libusb_exit.  That is
pyusb, but from looking at its source I would expect the init call to occur
only once at the beginning.

One aspect of the program that clutters up the logs is that I perform a
periodic check of all connected usb devices to see if a new device of a
certain type has been connected or disconnected.  Pyusb does not have any
asynchronous support, so I'm forced to continually enumerate all devices to
detect this.

Also cluttering the logs, the program was interacting with two devices when
these logs were recorded -- so the reads/writes for each are interlaces
throughout.

I typically perform short timeout usb reads and handle the timeout
appropriately.  The problematic timeouts are unusual in that they either
occur during a write() call (for which I specify a 1s timeout) or during
enumeration (in which pyusb calls libusb_get_device_list()).

I'll see if I can recreate this issue with only a single device connected.
And also if I can figure out why libusb_init() is being called so often.

Richard