Hi all,
i'm a programmer for a usb 2.0 audio device, and right now i'm programming for a big audio company. In Mac OS 10.4.2 there were a couple of issues in usb 2.0 isochronos ( the transaction type that realtime multimedia devices use )transactions. One big problem occurred only with write transactions, so transactions from the host to the device. Normally with isochronos transactions the system gives you realtime information to when a usb frame has completed and how much data was actually transfered. In Mac OS 10.4.2 and earlier this mechanism didn't work, meaning that you only got the information when a whole transaction completed, likely consisting of many 100 usb frames. The only workaround was to queue many transactions with little frame numbers, increasing system load dramatically. This is one of the main reasons why there are hardly any usb 2.0 audio devices out fot the mac. I filed a bug about this and i am in constant connection with people at Apple. And let me tell you this: to this day, they are having BIG problems correcting this. Well they did correct the just explained problem, but doing this, all of a suddon everthing else in usb started to fail. Right now, i don't know what they are doing but they seem to have major problems with usb 2.0
hogliux