-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Wed, 6 Nov 2002 03:08, Charlie Brady wrote: > There's something that I haven't been able to find clear and unambiguous > documentation on. Someone here might know. > > Will USB 2.0 devices work just fine, but at lower speed, on a USB 1.1 bus? USB 2.0 means different things to different people.
To the specification writers, USB 1.1 is historical, and USB 2.0 replaces it, cleaning up a number of "grey" areas, and adding an optional high-speed mode. Most of the changes to the spec are in Chapter 11 , which deals with hubs. To product makers, USB 2.0 is a new label that people look for. The less honest can rebadge the old USB 1.1 product as USB 2.0, probably without any redesign. "High speed" means that the device can work at 480Mbps (wirespeed - you'll never get to this level in application level data transfer). Note that the USB 2.0 spec also described "full speed" and "low speed". It is intended and entirely logical that people make USB 2.0 mice at 1.5Mpbs. The only design change that will be required for most devices is a better cable. To support "High speed", you need a host controller (the bit in the PC) that can support it. This time around, everyone agreed on a single PCI design, called Enhanced Host Controller Interface (EHCI). Note that EHCI _only_ handles high speed. There is a port multiplexer that can switch each port to either the EHCI controller proper, or to a "companion controller" which is OHCI in most plugin cards, and UHCI in Via and Intel chipsets. By default, each port comes up attached to one of the companion controllers. What this means is that if you put a USB 2.0 card in a machine that doesn't know how to initialise the EHCI controller, and you attach a USB 2.0 device (say an ISD300 based disk drive), then it will work in accordance with the USB 2.0 spec, at 12Mbps. If you add an EHCI driver to the USB host software, and replug, it should work at high speed. Linux support is pretty good, except that 2.4.19 (which was going to be the first production release) has a bug that it will oops if you unplug a USB 2.0 hub. You need to backport the USB changes from 2.4.20-pre > Has anybody used USB tape backup devices? Anything good or bad to report? Sorry, no. I wouldn't expect too many problems though. USB mass storage is really just a user of the SCSI interfaces. Brad - -- http://linux.conf.au. 22-25Jan2003. Perth, Aust. I'm registered. Are you? -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE9yCPlW6pHgIdAuOMRAkhxAKCrk7kMQQiYODGBopocPCbzZDXSegCcDtRf nfvH4dzRj3fYMW7Fr7rNFVg= =Y/9M -----END PGP SIGNATURE----- -- Please report bugs to [EMAIL PROTECTED] Please mail [EMAIL PROTECTED] (only) to discuss security issues Support for registered customers and partners to [EMAIL PROTECTED] To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Searchable archive at http://www.mail-archive.com/devinfo%40lists.e-smith.org
