On Mon, 5 Sep 2005, Franck wrote: > > On the other hand, it's not really all that much useless work. 4 times > > per second or so there's a single, very short transaction (IN followed by > > NAK). Unless you've got some good reason for avoiding it, why bother? > > > > Well, if work can be avoided without huge pain why bother to do it ? > Moreover I'm working on an embedded system where IRQ latency is quite > expensive...
It's up to you. Considering how rarely the problem is liable to arise, I wouldn't spend much time worrying about it. > > On the third hand, who would ever make an embedded hub with only one, > > fixed downstream port? Why not leave out the hub and attach the upstream > > port directly to the downstream device? > > > > surely because the downstream device is a high speed device ? That's not a good reason. The internal hub is also a high-speed device. What advantage is there in putting the hub between the device and the upstream port? > Here is > a bit of /proc/bus/usb/devices: > > T: Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 47 Spd=480 MxCh= 1 > D: Ver= 2.00 Cls=09(hub ) Sub=00 Prot=01 MxPS=64 #Cfgs= 1 > P: Vendor=067b ProdID=2515 Rev= 1.00 > S: Manufacturer=Prolific Technology Inc. > S: Product=USB Embedded Hub > C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=100mA > I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub > E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=256ms > > T: Bus=01 Lev=02 Prnt=47 Port=00 Cnt=01 Dev#= 48 Spd=480 MxCh= 0 > D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1 > P: Vendor=067b ProdID=2517 Rev= 1.00 > S: Manufacturer=Prolific Technology Inc. > S: Product=USB Mass Storage Device > C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr= 2mA > I: If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=05 Prot=50 Driver=usb-storage > E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms > E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms Okay, so Prolific actually did this. I still think it's going to be relatively rare and that the overhead will be minimal. Alan Stern ------------------------------------------------------- SF.Net email is Sponsored by the Better Software Conference & EXPO September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
