Re: [Haskell-cafe] Need comments on a libusb asynchronous select/poll loop

On 20 April 2011 17:04, Johan Tibell wrote:

On Tue, Apr 19, 2011 at 10:36 PM, Bas van Dijk wrote:

...

On 19 April 2011 15:06, John Obbele wrote:        -- Step 3 is the most important step. Submitting the transfer:        handleUSBException $ c'libusb_submit_transfer transPtr

       -- TODO: Now we need to do the complicated stuff described in:        -- http://libusb.sourceforge.net/api-1.0/group__poll.html        --        -- First we need the function:        -- getPollFds ∷ Ctx → IO [C'libusb_pollfd]        --        -- A C'libusb_pollfd:        -- http://libusb.sourceforge.net/api-1.0/structlibusb__pollfd.html        -- is a structure containing a file descriptor which should be        -- polled by the GHC event manager and an abstract integer        -- describing the event flags to be polled.        --        -- The idea is to call getPollFds and register the returned        -- file descriptors and associated events with the GHC event        -- manager using registerFd:        -- http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/System-Eve...        --        -- As the callback we use libusb_handle_events_timeout.        --        -- But here we run into a problem: We need to turn our        -- concrete event integer into a value of the _abstract_ type        -- Event. But the only way to create Events is by evtRead or        -- evtWrite!        --        -- I would really like a solution for this.        -- Bryan, Johan any ideas?

Could you do something like:

toEvent :: Int -> Event toEvent flag    | flag `xor` (#const POLLIN) = evtRead

etc?

Yes I think I can. I currently copied the code from GHC.Event.Poll: https://github.com/basvandijk/usb/blob/async/Poll.hsc

Not that evtRead and evtWrite maps to different things on different platforms.

Do you mean "Not" or "Note"? Thanks, Bas