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parse

descriptors()

Parse device descriptors looking for a speciﬁc entry

Synopsis:

#include <sys/usbdi.h>

usbd_descriptors_t *usbd_parse_descriptors(

struct usbd_device *device,

struct usbd_desc_node *root,

_uint8 type,

int index,

struct usbd_desc_node **node );

Arguments:

device The opaque handle for the device whose descriptors you want to search.

root Where in the tree to begin parsing (pass

NULL to start at the base).

type The type of descriptor to ﬁnd (

USB_DESC_*), or 0 to match any type.

index The occurrence of the descriptor that you want to ﬁnd.

node A pointer to a location where the function stores a pointer to the descriptor

that it found. You can use this as the root for future requests.

Library:

libusbdi

Description:

When you call it the ﬁrst time, the usbd

parse

descriptors() function loads all the

descriptors from the USB device:

• device

• conﬁguration

• interface

• endpoint

• hub

• string

The function uses usbd

descriptor() to get each raw USB descriptor. The data is then

endian-ized, made alignment-safe, and built into an in-memory tree structure to

facilitate future parsing requests.

Each node in this tree is a

struct usbd_desc_node. The root parameter lets you

say where in the tree to begin parsing (

NULL is base). The node parameter tells you

where a descriptor was found to root future requests from.

The tree looks like this:

September 10, 2007 Chapter 4 • USB Library Reference 61

1 2 ... 70 71 72 73 74 75 76 77 78 79 80 ... 106 107

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