hi: 2011/8/1 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Mon, 1 Aug 2011, loody wrote: > >> sorry for picking this old thread, since the subject is the same. >> my question is: >> In high speed device and an urb->inerval is less than 8, take 2 or 4 >> for example, the number of iso transfer descriptors will be >> 1+(span+7)/8. >> >> But the formula above seems to be used for urb-> interval =1, right? >> Why the # of iso transfer descriptors not to be span/interval but 1+(span+7)/8? > > Because each iTD provides information for an entire frame, i.e., 8 > microframes. The each micro-frame of iso transfer descriptors will not be filled except urb->interval is 1, right? if the urb->interval = 2, that mean the total number of iso transfer descriptors we need are (1+(span+7)/8)*2 not 1+(span+7)/8, since only half of iso transfer descriptors are filled with packets in iso sched. -- appreciate your help -- 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
