Messages in this thread | | | Date | Mon, 31 Mar 2003 11:51:02 -0800 | From | David Brownell <> | Subject | ANNOUNCE: Linux "USB Gadget" API and Driver Framework |
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WHAT This is a kernel-mode API, and an initial set of drivers for it, that helps Linux 2.4 and 2.5 kernels support intelligent "USB Device" (peripheral) hardware.
The code is ready for more general use by the Linux community, including development of new drivers. It supports network connections over USB "out of the box", using the NetChip 2280 USB 2.0 high speed controller, and is now being used with high speed USB devices running under Linux.
(Note that such an API is on the 2.5 wishlist. This is the first such API that was designed from the ground up to work with the existing host side Linux-USB stack, and to support USB 2.0 high speed devices.)
WHERE http://kernel.bkbits.net/~david-b/
Temporary web page with info, including: - gadget.pdf ... kerneldoc, in PDF format - gadget25-0331.patch ... patch for 2.5 - gadget24-0331.patch ... patch for 2.4
bk://kernel.bkbits.net/david-b/gadget-2.5 bk://kernel.bkbits.net/david-b/gadget-2.4
BitKeeper repositories
HELPING There are lots of opportunities to write drivers here, both for dozens more USB "class" specifications and, if you want to get down'n'dirty, for USB device controller hardware.
Please discuss this on the linux-usb-devel@lists.sourceforge.net mailing list, unless/until a new list gets set up.
DETAILS Since talking about a "USB Device Driver" becomes ambiguous when both sides of the protocol stack can run Linux, Linux-USB developers have chosen new terminology. A "USB Device Driver" is what current Linux kernels have: a Host-side driver. A Device-side driver is instead called a "USB Gadget Driver" ... that's why the new name.
The API is straightforward and thin, just one new header file to shape how "gadget" drivers talk to the underlying controller hardware. There is no "mid-layer" requirement, and all policy for device configuration and management goes above this API. I/O involves just submitting an asynchronous request to the relevant endpoint (like URBs but simpler).
There are currently two USB device controller drivers available implementing that API.
- The "net2280" driver supports the NetChip 2280 controller, which is a PCI device that supports USB 2.0 high speed transfers. (PCI card versions are available for development.)
- There's a "dummy_hcd" which provides partial emulation (bulk and control transfers) of a controller so that you can do some stages of development without real hardware. (Maybe with debug assistance from UML.) 2.5 only for now (got patch?).
This can emulate three kinds of hardware that are of interest to the Linux community: the net2280 (as above), the sa1100 (found in older PDAs), and the pxa25x (found in newer PDAs).
There are currently two gadget drivers using that API:
- "Gadget Zero" helps development and testing. One configuration sinks or sources data; the other one loops data sent out from the host back in to that host. Almost any USB controller can support this driver. You can start a new driver from this one by "clone and modify" (using new vendor and product IDs).
- There's a CDC Ethernet gadget driver, letting you use USB as a network link. It talks to the standard Linux "CDCEther" (2.4) or "cdc-ether" (2.5) drivers, or corresponding class drivers that are found on other operating systems. (It's analagous to the ARM Linux sa1100 "usb-eth" driver; but more standard.)
You'll want some recent patches to those drivers, or the latest 2.5 "usbnet" for performance. (18+ Mbyte/sec at high speed, using TTCP in one direction, vs 4+ MByte/sec; no tuning yet.)
Both of those gadget drivers have compile-time configuration support to let them work with net2280, pxa25x, or sa1100 usb drivers. Each controller has slightly different endpoint capabilities; gadget drivers must choose endpoints and configurations accordingly, and there's no point in trying to do that at run time.
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