On Wed, 20 Jul 2005, Hoang Tran wrote: > *ISSUE* > > Wireless WAN PC Card modem devices such as the Novatel Merlin V620/S620 > and Kyocera KPC650 on a 1xEV-DO network experience a stalled data > connection due to high data rates when operated on Linux kernel 2.4.x > and 2.6.x. This issue does not occur when the cards are connected at > 1xRTT data rates. > > *BACKGROUND* > > The affected modems are PCMCIA cards that use a USB host controller > interface to expose a serial device to the Linux operating system. The > generic usbserial driver can be used to talk to these devices as if they > were serial modems. > > There are 2 potential problems that this work-around resolves: > > 1. The current usbcore and usbserial driver do not correctly recognize > the maximum packet size on the inbound bulk endpoint. > 2. The cards themselves are not advertising the correct maximum data > packet size to the usb sub-system on Linux. > > By default the linux usb core sees only 64 bytes of capacity. Without > this work-around there is no way to specify what the maximum packet size > on the inbound bulk endpoint should be. If you consider that the MTU on > these cards is set at 1500 and the usb bulk endpoint callbacks are only > reading 64 bytes at a time off of the serial tty, it doesn't take long > to start dropping packets and seriously junkify your connection.
You have confused packet size with buffer size. Full-speed bulk endpoints must have a maxpacket size <= 64 and high-speed bulk endpoints must have maxpacket <= 512; that is part of the USB specification. But packet size is not directly related to buffer size, because a buffer can be transferred using multiple packets. Alan Stern ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
