NAME
usbhid, hid_get_report_desc, hid_use_report_desc, hid_dispose_report_desc, hid_start_parse, hid_end_parse, hid_get_item, hid_report_size, hid_locate, hid_usage_page, hid_usage_in_page, hid_init, hid_get_data, hid_set_data — USB HID access routines
LIBRARY
USB Human Interface Devices Library (libusbhid, −lusbhid)
SYNOPSIS
#include <usbhid.h>
report_desc_t
hid_get_report_desc(int file);
report_desc_t
hid_use_report_desc(unsigned char *data, unsigned int size);
void
hid_dispose_report_desc(report_desc_t d);
hid_data_t
hid_start_parse(report_desc_t d, int kindset, int id);
void
hid_end_parse(hid_data_t s);
int
hid_get_item(hid_data_t s, hid_item_t *h);
int
hid_report_size(report_desc_t d, hid_kind_t k, int id);
int
hid_locate(report_desc_t d, u_int usage, hid_kind_t k, hid_item_t *h, int id);
char *
hid_usage_page(int i);
char *
hid_usage_in_page(u_int u);
int
hid_parse_usage_page(const char *);
char *
hid_parse_usage_in_page(const char *);
void
hid_init(char *file);
int
hid_get_data(void *data, hid_item_t *h);
void
hid_set_data(void *data, hid_item_t *h, u_int data);
DESCRIPTION
The usbhid library provides routines to extract data from USB Human Interface Devices.
Introduction
USB HID devices send and receive data layed out in a device
dependent way. The usbhid library contains routines
to extract the report descriptor which contains the
data layout information and then use this information.
The routines can be divided into four parts: extraction of the descriptor, parsing of the descriptor, translating to/from symbolic names, and data manipulation.
Descriptor
Functions
A report descriptor can be obtained by calling
hid_get_report_desc() with a file descriptor obtained
by opening a uhid(4) device. Alternatively a data buffer
containing the report descriptor can be passed into
hid_use_report_desc(). The data is copied into an
internal structure. When the report descriptor is no longer
needed it should be freed by calling
hid_dispose_report_desc(). The type
report_desc_t is opaque and should be used when
calling the parsing functions. If
hid_dispose_report_desc() fails it will return
NULL.
Descriptor
Parsing Functions
To parse the report descriptor the hid_start_parse()
function should be called with a report descriptor and a set
that describes which items that are interesting. The set is
obtained by OR-ing together values (1 << k)
where k is an item of type hid_kind_t. The
report ID (if present) is given by id. The function
returns NULL if the initialization fails, otherwise an
opaque value to be used in subsequent calls. After parsing
the hid_end_parse() function should be called to free
internal data structures.
To iterate through all the items in the report descriptor hid_get_item() should be called while it returns a value greater than 0. When the report descriptor ends it will returns 0; a syntax error within the report descriptor will cause a return value less than 0. The struct pointed to by h will be filled with the relevant data for the item. The definition of hid_item_t can be found in <usbhid.h> and the meaning of the components in the USB HID documentation.
Data should be read/written to the device in the size of the report. The size of a report (of a certain kind) can be computed by the hid_report_size() function. If the report is prefixed by an ID byte it is given by id.
To locate a single item the hid_locate() function can be used. It should be given the usage code of the item and its kind and it will fill the item and return non-zero if the item was found.
Name
Translation Functions
The function hid_usage_page() will return the
symbolic name of a usage page, and the function
hid_usage_in_page() will return the symbolic name of
the usage within the page. Both these functions may return a
pointer to static data.
The functions hid_parse_usage_page() and hid_parse_usage_in_page() are the inverses of hid_usage_page() and hid_usage_in_page(). They take a usage string and return the number of the usage, or −1 if it cannot be found.
Before any of these functions can be called the usage table must be parsed, this is done by calling hid_init() with the name of the table. Passing NULL to this function will cause it to use the default table.
Data
Extraction Functions
Given the data obtained from a HID device and an item in the
report descriptor the hid_get_data() function
extracts the value of the item. Conversely
hid_set_data() can be used to put data into a report
(which must be zeroed first).
EXAMPLES
Not yet.
FILES
/usr/share/misc/usb_hid_usages
The default HID usage table.
BUGS
This man page is woefully incomplete.
SEE ALSO
The USB specifications can be found at http://www.usb.org/developers/docs/.
HISTORY
The usbhid library first appeared in NetBSD 1.5.
BSD December 29, 2001 BSD