USBHID(3) BSD Library Functions Manual USBHID(3)NAME
usbhid, hid_get_report_desc, hid_get_report_id, 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
USB Human Interface Devices Library (libusbhid, -lusbhid)
hid_set_immed(int fd, int enable);
hid_use_report_desc(unsigned char *data, unsigned int size);
hid_start_parse(report_desc_t d, int kindset, int id);
hid_get_item(hid_data_t s, hid_item_t *h);
hid_report_size(report_desc_t d, hid_kind_t k, int id);
hid_locate(report_desc_t d, u_int usage, hid_kind_t k, hid_item_t *h,
const char *
const char *
hid_parse_usage_page(const char *);
hid_parse_usage_in_page(const char *);
hid_init(const char *file);
hid_get_data(const void *data, const hid_item_t *h);
hid_set_data(void *buf, const hid_item_t *h, int data);
The usbhid library provides routines to extract data from USB Human
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
The routines can be divided into four parts: extraction of the descrip‐
tor, parsing of the descriptor, translating to/from symbolic names, and
Synchronous HID operation
Synchronous HID operation can be enabled or disabled by a call to
hid_set_immed(). If the second argument is zero synchronous HID opera‐
tion is disabled. Else synchronous HID operation is enabled. The func‐
tion returns a negative value on failure.
The report descriptor ID can be obtained by calling hid_get_report_id().
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, oth‐
erwise an opaque value to be used in subsequent calls. After parsing the
hid_end_parse() function should be called to free internal data struc‐
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
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).
/usr/share/misc/usb_hid_usages The default HID usage table.
The USB specifications can be found at
The usbhid library first appeared in NetBSD 1.5.
This man page is woefully incomplete.
BSD January 27, 2009 BSD