Hi Folks, I am seeing something strange on a test machine, and I am not sure if I am doing something wrong, or if I have found a bug in OS X.
I have a SS device that supports Isoch. I am using the GetBandwidthAvailable() call from IOUSBLib to see how much bandwidth is available for the device. I am running on MacBookPro10,1 and the machine is running 10.8.5. If I plug the device into the USB port on the left hand side of the machine, the GetBandwidthAvailable() call returns 144 bytes per isoch period (e.g. 1.1 MB/s or so). If I plug the device into the USB port on the right hand side of the machine, the GetBandwidthAvailable() call returns 56240 bytes per isoch period (e.g. 449 MB/s or so). If I run USB Prober and logging, I get: Left hand side of the machine: Apr 14 20:12:10.740 [2] AppleUSBXHCI::GetBandwidthAvailableForRootHubPort - port(5) portSpeed (0) deviceSpeed(3) - bandwidthAvailableInBlocks (1156) - returning (144) Right hand side of the machine: Apr 14 19:57:06.825 [2] AppleUSBXHCI::GetBandwidthAvailableForRootHubPort - port(6) portSpeed (3) deviceSpeed(3) - bandwidthAvailableInBlocks (3515) - returning (56240) It seems like the AppleUSBXHCI driver thinks that the root-hub port speed is FS for the left hand port, vs. SS for the right hand port. Is this an OS bug (fixable by going to a newer OS), a HW bug, or something I am doing wrong? I have not tried to start streaming on the EPs yet, but it seems like the overall behavior of the GetBandwidthAvailable() is a bit weird on that port, because when I set the alternate for the interface that actually has the isoch ports, it succeeds. The Isoch EPs are configured to be 1024 bytes per packet, with a polling interval of 1ms (8 micro frames). This means that each EP should be consuming 1MB/s or so, but when that alt is selected, the result from GetBandwidthAvailable() only goes down to 112 (896,000 bytes/second). Does this mean that the bandwidth will actually be available on the port, and that the GetBandwidthAvailable() call is returning incorrect data for that port, or is the bandwidth more limited than one would expect on that port? Thanks! _______________________________________________ Do not post admin requests to the list. They will be ignored. Usb mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/usb/archive%40mail-archive.com This email sent to [email protected]
