UM0851 datasheet(71/245 Pages) STMICROELECTRONICS

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UM0851

Communication device drivers

Doc ID 16604 Rev 2

71/245

Figure 16.

USBD software architecture

As shown in the figure above, the gadget drivers can access the USB Device driver either

directly through the gadget framework or through the composite layer. The composite layer

provides an interface where multi-functional devices (like audio and video) can be easily

supported. It is preferable that USB gadget drivers who do not have composite features also

interact through the composite layer.

Note:

Please note that only one gadget driver at a time can exist in this framework using gadget

framework. Also remember that composite layer is in itself a gadget drive. Therefore

according to the figure, the printer and the composite layer cannot exist at the same time.

One possibility is to build the printer gadget over the composite layer.

The remaining part of this document describes the composite layer interface. For detailed

documentation on the gadget framework please refer to:

http://www.linux-usb.org/gadget/

In the Linux source tree, the USBD controller driver is present in:

drivers/usb/gadget/spr_udc_syn.c

4.4.3

USBD driver interface with Linux gadget layer

As mentioned above, the USB Device controller driver supports Linux gadget framework.

For this, it exports certain device and endpoint specific routines and exports two functions

for registering and un-registering to the framework.

/* device specific operations exported by usbd driver */

static const struct usb_gadget_ops spear_udc_dev_ops = {

.get_frame = spear_dev_get_frame,

.wakeup = spear_dev_wakeup,

.set_selfpowered = spear_set_selfpowered,

Hardware

Kernel space

User space

ifconfig

mount

Ethernet (usb0)

File storage

Printer

Composite device

USB gadget framework

USBD driver

USBD device controller

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