JackOfAll wrote: > Remind me about the need for an external hub. This is for Class 1 > devices, where the controller doesn't deal with split transactions and > the hub is needed between the host controller and the device? Or there > isn't a TT at all for anything other than HIGH_SPEED, so FULL and LOW > need the hub TT? >
Only needed for full speeds uac devices (class 1) on arm SoC which have a restricted TT - Touch, CuBox and serveral others all show this limitation. In this case the TT can do split transactions, but from hacking the ehci scheduler on Touch I've shown that it doesn't support a inbound and outbound iso split transaction in the same 1ms frame. [which given that uac1 devices normally ask for 1 outbound packet per ms causes a big problem for async usb - this causes what we see with Touch, the async feedback mechanism doesn' work unless we add on an external hub]. It looks like its a cost cutting optimisation of the ehci implementation which is normally no problem, but causes async dacs a problem. [The EDO kernel has a hack to ignore the request and schedule outbound every 2ms, so the inbound can be scheduled on differnent frames - this is the "no hub workaround" which you will see if you have such a dac in the EDO menus] ------------------------------------------------------------------------ Triode's Profile: http://forums.slimdevices.com/member.php?userid=17 View this thread: http://forums.slimdevices.com/showthread.php?t=97881 _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/discuss
