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Includes the latest and most frequently asked questions regarding protocol products covering Bluetooth, DDR3 & DDR4, Ethernet, Fibre Channel, IEEE1394, Infiniband, PCI Express, PCI/PCI-X, SAS, SATA, USB, and others.

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Optimization for Trace collection on USB traffic


I have USB devices I am writing a multi-device USB downloader for. I can download to 4 devices without any problems. As soon as I place a 5th device into the procedure I get failures.


First the best location for the primary channel is normally as you say between the root port and the hub. But don't forget the secondary channel can be placed independently between the hub and one of the devices.

The recording options you probably want are, first to set the buffer to maximum. Then choose event trigger mode and set the pre/post trigger slider to the right so that you get mostly the traffic up to the trigger point.

As you suggest triggering on the bus reset this is quite easy on the events tab choose bus conditions and choose bus reset. But remember that the bus reset from the root port only resets the hub, the device bus reset will be seen on the root to hub link as a port reset command for the hub - hence the need for two recording channels. Otherwise you would want to trigger on the data pattern for the hub port reset for whichever hub port you want to trigger on. Note that hub ports would be reset during enumeration so if you are triggering on the hub-port command (or bus reset) you may want to add a counter on the actions tab to trigger on the second or nth event as required

In addition to this you can save memory if you need to by selecting the truncate data field option on the first tab. This will filter out all but the first 8 bytes of the each transfer for the download.



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