[Twisted-Python] libusb-1 file descriptors

gelin yan dynamicgl at gmail.com
Sun Feb 12 13:37:28 EST 2012

On Sun, Feb 12, 2012 at 7:10 PM, Phil Mayers <p.mayers at imperial.ac.uk>wrote:

> On 02/12/2012 04:13 AM, Donal McMullan wrote:
> > I'm trying to integrate Twisted with libusb-1
> >
> > The libusb-1 Python wrapper offers a USBPoller class to "allow
> > integration of USB event polling in a file-descriptor monitoring event
> > loop." The class expects to receive a 'poller' object, again quoting
> > from the documentation:
> >
> >      poller is a polling instance implementing the following methods:
> >      - register(fd, event_flags)
> >        event_flags have the same meaning as in poll API (POLLIN&
> >      - unregister(fd)
> >      - poll(timeout)
> >        timeout being a float in seconds, or None if there is no timeout.
> >        It must return a list of (descriptor, event) pairs.
> >      Note: USBPoller is itself a valid poller.
> >
> > I feel like it should be obvious, but I can't see what would be the
> > correct way to integrate this with Twisted. My particular application
> > is to enable networking over the ANT+ protocol via a small USB key.
> I've only quickly scanned it, but actually it doesn't look obvious to me
> at all.
> I *think* that you want to ignore USBPoller entirely; it looks like it's
> some sort of mini reactor thing, although it's not obvious to me how it
> ever DOES anything.
> USBContext looks to be the "thing" that you plug in an event loop to.
> However, I'm not certain (perhaps others will comment) that it makes
> sense to integrate it into the Twisted event loop - the file descriptor
> "ready" events don't seem to trigger corresponding "read" events, and
> the USB protocol implementation isn't accessible, so the Twisted model of:
>  file ready event -> transport does read -> protocol dataReceived
> ...doesn't really apply.
> It may be just as easy to write wrapper around your protocol in plain
> non-Twisted python, and talk to it from Twisted over a
> pipe/process/whatever.
>  the most simplest way is probably to use another thread to handle all
possible events and use twisted's thread functions to
leverage the whole system though it is inefficient.

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