a quick read on endpoints and transfer types mention "interrupt" transfer.
now wondering, if such kind of transfer is available, is it upto the
driver to call read again-n-again (as per the interrupt frequency) ?
The standard technique for this if for the driver to leave an
asynchronous read (or pool of reads) outstanding -- this causes the
host controller to poll the device at the frequency specified in the
device's descriptors and, whenever it send a packet, one of the async
reads completes.
The calling of the completion proc is the "interrupt" as far as the
software layers above are concerned.
or will the host controller driver understand that a device down below
has interrupt data, and would call my driver's completion routine ?
USB is a purely a master/slave polled bus. No device talks unless
polled by the host controller.
The host controller only polls devices/endpoints if there's a read
outstanding for them.
The only type of I/O supported by the is hardware is asynchronous --
synchronous reads are faked in the host software by issuing an
asynchronous read and blocking until a library-supplied completion
routine is called.
Libraries like libusb attempt to hide the way USB really works in an
attempt to make it look like unix file I/O and cause inefficency and
confusion as a result.
(A related issue is hiding the packet-oriented nature of bulk transfers)
i think i need to read the USB specs carefully, before i jump the gun....
Read the archives of this list as well -- this (and related topics)
come up every 3-6 months.
That's not to say it isn't worth discussing -- it's non-trivial and
in many cases non-obvious.
If you're working on libusb you should understand it because, having
looked at it, libusb has exposes a bunch of stuff it shouldn't
(busses, device numbers) and hides stuff that should be exposed
(packet nature of bulk).
HTH,
-Steve
--
_________________________________________________________________________
Steve Sisak, CTO email@hidden
IOXperts, Inc. +1 617 876-2572
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