Parse device descriptors looking for a specific entry


#include <sys/usbdi.h>

usbd_descriptors_t *usbd_parse_descriptors( 
                      struct usbd_device *device, 
                      struct usbd_desc_node *root, 
                      uint8_t type,
                      int index,
                      struct usbd_desc_node **node );


The opaque handle for the device whose descriptors you want to search.
Where in the tree to begin parsing (pass NULL to start at the base).
The type of descriptor to find (USB_DESC_*), or 0 to match any type.
The occurrence of the descriptor that you want to find.
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.




When you call it the first time, the usbd_parse_descriptors() function loads all the descriptors from the USB device:

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:

    (CONFIG)  -  .....   (CONFIG)
      (INTERFACE)  -  .....    (INTERFACE)
        (ENDPOINT)  -  .....    (ENDPOINT)

Any vendor-specific or class-specific descriptors that are embedded into the standard descriptor output are also inserted into this tree at the appropriate point.

Although a descriptor for endpoint 0 (control) isn't present on the wire, one is constructed and placed in the tree (to simplify enumeration within the class driver).

You use type for specifying the type of descriptor to find; index is the nth occurrence. Note that type 0 will match any descriptor type; you can use it to retrieve any embedded class or vendor-specific descriptors if you don't know their type.

Here's an example that will walk all endpoints for an interface:

for (eix = 0; (desc = usbd_parse_descriptors(device, ifc, USB_DESC_ENDPOINT, 
                eix, &ept)) != NULL; ++eix)

where ifc is the appropriate (INTERFACE) node (found by a previous call to usbd_parse_descriptors() or usbd_interface_descriptor().


A pointer to the descriptor on success, or NULL on error.


QNX Neutrino, QNX 4

Cancellation point No
Interrupt handler No
Signal handler No
Thread Yes

See also:

usbd_args_lookup(), usbd_configuration_descriptor(), usbd_descriptor(), usbd_device_lookup(), usbd_device_extra(), usbd_device_descriptor(), usbd_endpoint_descriptor(), usbd_hcd_info(), usbd_hub_descriptor(), usbd_interface_descriptor(), usbd_languages_descriptor(), usbd_string(), usbd_urb_status()