On Sat, 7 Sep 2013, vichy wrote: > hi all: > when I trace linux ehci driver source code. > I have some questions > 1. in itd_slot_ok, why we have to > uframe %= period; > and use this uframe to calculate the bandwidth? > > suppose start passed to itd_slot_ok is 537, period, usb->interval, is 8. > that mean we want to know whether bandwidth of microframe 537 is enough. > Not want to know whether 537%8 =1 > the bandwidth of microframe 1 is enough. In fact you need to know both. If an isochronous endpoint has interval 8 and it uses microframe 537, then it's also going to use microframes 545, 553, 561, ..., 8177, 8185, 1, 9, ..., 529. > 2. Below is part of message excerpted from usb mon log: > db1e2000 81051026 S Zi:1:002:6 -115:8:5327 1 -18:0:132 132 < > db1e2000 81058043 C Zi:1:002:6 0:8:5391:0 1 0:0:4 132 = 2efd82fd > 0cfeffff 84feb3ff 98fec4fb 08ffdaf8 060059fb 8b01d2ff db02de01 > > why these 2 ep->start_frame are different, 5327 in "-115:8:5327" and > 5391 in "0:8:5391:0"? > > The log is captured with the same urb, for submitting and completing. > That mean ep->start_frame=urb->start_frame in submit and complete > should be the same, right? No. The value in urb->start_frame during submission is meaningless. Usually it is left over from the last time urb was used. After the URB is submitted, the host controller driver stores the correct value in urb->start_frame, and usbmon shows the correct value during completion. Alan Stern -- 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
