g...@novadsp.com wrote:
> Once I have opened a device using LibUsbX, is there a
> synchronization handle I can pend on whilst waiting for the
> peripheral device to write back to the host?
The device is not allowed to transmit to the host before your
application requests data.
> // open device etc.
> libusb_open_device_with_vid_pid(NULL,m_args.VID,m_args.PID);
> while (!done)
> {
> DWORD dw = WaitForMultipleObjects(handles.size(),&handles[0],FALSE,10);
> // data waiting to be read from device
> if (dw == WAIT_OBJECT_0 + 0)
> {
> // do the read ...
> result = libusb_bulk_transfer(m_pDevice,m_epIn,...);
> }
> // ....
> }
No good since there can be no data from device until you initiate a
transfer.
Another point is that the code is absolutely unportable, which kindof
misses one big point of using the portable libusb-1.0 API.
I recommend to create one USB event handling thread (which you may
already have) that calls libusb_handle_events_completed() in a loop,
and then you can choose per transfer if you want to perform a
synchronous transfer like in the call above where
libusb_bulk_transfer() will return when the requested data has been
transfered, or if you want to use the asynchronous API and queue a
transfer for processing an get a callback notification once it is
done, but be able to continue your own processing meanwhile.
//Peter
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