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Test Your Knowledge in Computers #600
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Functions in C do not need be declared before they can be used.
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struct_usb_configuration(9) [centos man page]

STRUCT 
USB_CONFIGURA(9) Kernel Mode Gadget API STRUCT USB_CONFIGURA(9) NAME
struct_usb_configuration - represents one gadget configuration SYNOPSIS
struct usb_configuration { const char * label; struct usb_gadget_strings ** strings; const struct usb_descriptor_header ** descriptors; void (* unbind) (struct usb_configuration *); int (* setup) (struct usb_configuration *,const struct usb_ctrlrequest *); u8 bConfigurationValue; u8 iConfiguration; u8 bmAttributes; u16 MaxPower; struct usb_composite_dev * cdev; }; MEMBERS
label For diagnostics, describes the configuration. strings Tables of strings, keyed by identifiers assigned during bind() and by language IDs provided in control requests. descriptors Table of descriptors preceding all function descriptors. Examples include OTG and vendor-specific descriptors. unbind Reverses bind; called as a side effect of unregistering the driver which added this configuration. setup Used to delegate control requests that aren't handled by standard device infrastructure or directed at a specific interface. bConfigurationValue Copied into configuration descriptor. iConfiguration Copied into configuration descriptor. bmAttributes Copied into configuration descriptor. MaxPower Power consumtion in mA. Used to compute bMaxPower in the configuration descriptor after considering the bus speed. cdev assigned by usb_add_config() before calling bind(); this is the device associated with this configuration. DESCRIPTION
Configurations are building blocks for gadget drivers structured around function drivers. Simple USB gadgets require only one function and one configuration, and handle dual-speed hardware by always providing the same functionality. Slightly more complex gadgets may have more than one single-function configuration at a given speed; or have configurations that only work at one speed. Composite devices are, by definition, ones with configurations which include more than one function. The lifecycle of a usb_configuration includes allocation, initialization of the fields described above, and calling usb_add_config() to set up internal data and bind it to a specific device. The configuration's bind() method is then used to initialize all the functions and then call usb_add_function() for them. Those functions would normally be independent of each other, but that's not mandatory. CDC WMC devices are an example where functions often depend on other functions, with some functions subsidiary to others. Such interdependency may be managed in any way, so long as all of the descriptors complete by the time the composite driver returns from its bind routine. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 STRUCT USB_CONFIGURA(9)

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STRUCT 
USB_COMPOSITE(9) Kernel Mode Gadget API STRUCT USB_COMPOSITE(9) NAME
struct_usb_composite_driver - groups configurations into a gadget SYNOPSIS
struct usb_composite_driver { const char * name; const struct usb_device_descriptor * dev; struct usb_gadget_strings ** strings; int (* bind) (struct usb_composite_dev *); int (* unbind) (struct usb_composite_dev *); void (* suspend) (struct usb_composite_dev *); void (* resume) (struct usb_composite_dev *); }; MEMBERS
name For diagnostics, identifies the driver. dev Template descriptor for the device, including default device identifiers. strings tables of strings, keyed by identifiers assigned during bind and language IDs provided in control requests bind (REQUIRED) Used to allocate resources that are shared across the whole device, such as string IDs, and add its configurations using usb_add_config(). This may fail by returning a negative errno value; it should return zero on successful initialization. unbind Reverses bind(); called as a side effect of unregistering this driver. suspend Notifies when the host stops sending USB traffic, after function notifications resume Notifies configuration when the host restarts USB traffic, before function notifications DESCRIPTION
Devices default to reporting self powered operation. Devices which rely on bus powered operation should report this in their bind() method. Before returning from bind, various fields in the template descriptor may be overridden. These include the idVendor/idProduct/bcdDevice values normally to bind the appropriate host side driver, and the three strings (iManufacturer, iProduct, iSerialNumber) normally used to provide user meaningful device identifiers. (The strings will not be defined unless they are defined in dev and strings.) The correct ep0 maxpacket size is also reported, as defined by the underlying controller driver. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 2.6. July 2010 STRUCT USB_COMPOSITE(9)

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