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POUser mode USB isochronous transfer from device-to-host
 

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  1. POUser mode USB isochronous transfer from device-to-host
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    <p>I am currently trying to interface with a USB audio device from user land. I currently have the device fully enumerated and I've set the interface and set the alternative interface to the interface non-zero-bandwidth alternative interface.</p> <p>Firstly I have to say I can't use anything like libusb. I ned to do this via Linux's USB device file system.</p> <p>So as far as I can tell I'm ready to begin receiving isochronous data. However I can find very little information on how to do an isochronous transfer.</p> <p>From what I can tell I need to populate a usbdevfs_urb structure but I'm completely unsure of how exactly to fill this structure.</p> <p>Also, once I have filled this structure am I right in thinking I need to call the following:</p> <pre><code>int retSubmit = ioctl( fd, USBDEVFS_SUBMITURB, &amp;usbRequest ); </code></pre> <p>and then once submitted I can wait for the request to complete using</p> <pre><code>USBDEVFS_REAPURBNDELAY </code></pre> <p>In the case of REAPURBNDELAY what exactly is the parameter I need to pass?</p> <p>Am I even barking up the right tree? </p> <p>Any information would be massively appreciated.</p> <p>Thanks in advance!</p> <p>Edit:</p> <p>I attempt to do the isochronous transfer as follows:</p> <pre><code>usbdevfs_urb&amp; urbRequest = *(usbdevfs_urb*)malloc( 384 ); urbRequest.type = USBDEVFS_URB_TYPE_ISO; urbRequest.endpoint = mpEndpoint-&gt;GetEndpointAddress();//mpEndpoint-&gt;GetEndpointIndex(); urbRequest.status = 0; urbRequest.flags = USBDEVFS_URB_ISO_ASAP; urbRequest.buffer = pData; urbRequest.buffer_length = 0; urbRequest.actual_length = 0; urbRequest.start_frame = 0; urbRequest.number_of_packets = 1; urbRequest.error_count = 0; urbRequest.signr = 0; urbRequest.usercontext = pData; usbdevfs_iso_packet_desc* pIsoPacketDesc = &amp;urbRequest.iso_frame_desc[0]; pIsoPacketDesc-&gt;length = 384; pIsoPacketDesc-&gt;actual_length = 0; pIsoPacketDesc-&gt;status = 0; </code></pre> <p>Unfgortunately this gives me an error of -28 (ENOSPC).</p> <pre><code>&lt;7&gt;[ 3184.243163] usb 1-1: usbfs: usb_submit_urb returned -28 </code></pre> <p>I can't understand why there wouldn't be enough usb bus bandwidth. There is only 1 usb port and my device is the only device plugged into it. </p> <p>Any thoughts?</p>
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    1. COWhy can't you use libusb?
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    2. CO@Jim Clay Because the specific platform in question is android and I already have an open file descriptor and I can't, due to permissions, open a device using libusb ...
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    3. COHi Goz, I'm currently trying to solve the same problem - that of isochronous transfers on android, avoiding libusb. Is there any way you would post a working code sample? My sticking point currently is struct definitions and request values. Where are you sourcing these? Thanks in advance.
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