NAME
usbhid
,
hid_get_report_desc
,
hid_use_report_desc
,
hid_dispose_report_desc
,
hid_get_report_desc_data
,
hid_start_parse
,
hid_end_parse
, hid_get_item
,
hid_report_size
, hid_locate
,
hid_usage_page
,
hid_usage_in_page
,
hid_parse_usage_page
,
hid_parse_usage_in_page
,
hid_start
, hid_init
,
hid_get_data
, hid_set_data
— USB HID access
routines
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);
void
hid_get_report_desc_data
(report_desc_t
d, uint8_t **data,
uint32_t *size);
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);
const char *
hid_usage_page
(int
i);
const char *
hid_usage_in_page
(u_int
u);
int
hid_parse_usage_page
(const
char *);
int
hid_parse_usage_in_page
(const
char *);
void
hid_init
(char
*file);
int
hid_start
(char
*file);
int32_t
hid_get_data
(void
*data, hid_item_t
*h);
void
hid_set_data
(void
*data, hid_item_t
*h, int32_t
data);
DESCRIPTION
The usbhid
library provides routines to
extract data from USB Human Interface Devices.
INTRODUCTION
USB HIDs send and receive data laid 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 which can be accessed with
hid_get_report_desc_data
().
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.
hid_get_report_desc
() and
hid_use_report_desc
() return
NULL on failure.
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 are interesting. The set is obtained by or-ing together values
(1 << k) where k is an
item of type hid_kind_t. The desired report ID, or -1
to obtain items of all report IDs, 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 return 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_start
()
with the name of the table. Passing NULL to this
function will cause it to use the default table. A return value of -1
indicates that an error has occurred, and errno is
set.
DATA EXTRACTION FUNCTIONS
Given the data obtained from a HID 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).
FILES
/usr/share/misc/usb_hid_usages The default HID usage table.
SEE ALSO
The USB specifications can be found at: https://www.usb.org/documents/
HISTORY
The usbhid
library first appeared in
OpenBSD 3.0.
BUGS
This man page is woefully incomplete.