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List:       libusb-devel
Subject:    Re: [libusb] Handle events of an isochronous transfer OUT
From:       Tim Roberts <timr () probo ! com>
Date:       2016-07-03 19:12:30
Message-ID: 82889AA9-F827-452F-BCE3-AEA0FE13B414 () probo ! com
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On Jul 2, 2016, at 11:13 AM, Matías Araujo <matiasaraujo88@gmail.com> wrote:
> 
> Hi, I want to implement an USB isochronous transfer OUT using libusb for a
> multi-threading application. I'm thinking on the design and I have some
> doubts:
> 
> 1.a) How should I use the libusb_handle_events function if I need to fill
> the buffer for every transfer in real time?

Yes.  Well, you probably want to fill and submit two transfers to begin with, so the \
buffer never has a chance to run dry.  When you get notified of a completion, you \
refill it and resubmit it.


> 1.b) Is it OK to do the filling of the new buffer for the transfer in the
> callback function? so once a transfer has finished I can send the next one
> with the new buffer.

Yes, that's what it takes.


> 1.c) Should I use an libusb_handle_events_completed and when the transfer is
> completed fill a new transfer and submit it.

Isn't that what you just said?


> 2)  Will it be right to not use libusb_handle_events and just fill the
> transfer and submit it?. I think my implementation will something like this:

What you showed is an infinite loop with no pacing.  Such a loop will flood the \
kernel with requests until it runs out of memory.  You need to pace things so you \
keep the list of pending requests at a relatively constant size.  For that, you have \
to use the events callback. — 
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

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