On Mon, Mar 30, 2015 at 11:58:55AM -0400, Alan Stern wrote: > On Mon, 30 Mar 2015, Johannes Stezenbach wrote: > > > > > Is it? I would expect a single 192 byte packet here, breaking > > it in two doesn't make sense even if the hub would be able > > to reassemble the parts. My recollection of the SPLIT mechanism > > is to free up the HS bus between FS send and FS ACK for other > > transactions on other hub ports, not to split the data packets. > > You have to get down into the gritty details. They are explained in > the USB spec, if you're curious. Basically, the idea is that the > transfer gets broken up into pieces, each of which is more or less > capable of fitting in a single microframe (125 us = 188 bytes of FS > data, approximately). > > As far as I can tell, it was done this way so as to minimize the amount > of data a hub would have to store and forward -- a bad tradeoff since > it increases driver complexity while saving only a few KB of storage (a > completely negligible amount nowadays). Thanks for the explanation, our emails just crossed as it took me too long to prepare mine. So it looks like to be a hub issue. Will try some other hubs. Thanks, Johannes -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
