Dear Alan, my question: when uvc driver submit new urb, in iso_stream_schedule calculate starting microframe for new urb, the location maybe in next round of periodic list. then how to process this condition? in this condition, the location of "now" may after starting microframe of new urb, right? Thanks a lot ! Soho 2011/6/3 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Fri, 3 Jun 2011, Soho Soho123 wrote: > >> Soho: is there any tolerance of index for iso schedule? > > The driver does not provide an index. The first time an URB is > submitted for an isochronous endpoint, iso_stream_schedule() picks a > starting microframe. Every time after that, each new URB is scheduled > for the first available index following the end of the previous URB. > >> soho: about maintenance of periodic schedule list, >> 1. >> like we can see some code get index from h/w by ehci_readl(ehci, >> &ehci->regs->frame_index) % mod, how about the purpose of % mod >> after get index from h/w > > mod is the length of the periodic list * 8. It is calculated from the > Frame List Size bits in the USBCMD register, so it can be 8092, 4096, > or 2048. > > The value of mod is multiplied by 8 because it is in microframes (like > the FRINDEX register), not in frames. > >> 2. >> like stream->next_uframe is use by driver (software). >> Do you have flow chart to explan how to link urb to h/w periodic list >> and remove it from h/w? > > The driver doesn't link URBs into the hardware periodic list; it links > iTDs. The code is in itd_link() and itd_complete(). > > For each URB, the driver only has to calculate the starting microframe. > This is done in iso_stream_schedule(). > > 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
