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Dd May 21, 2022
Dt USBHID 3
Os
Sh NAME
Nm usbhid ,
Nm hid_get_report_desc ,
Nm hid_use_report_desc ,
Nm hid_dispose_report_desc ,
Nm hid_start_parse ,
Nm hid_end_parse ,
Nm hid_get_item ,
Nm hid_report_size ,
Nm hid_locate ,
Nm hid_usage_page ,
Nm hid_usage_in_page ,
Nm hid_parse_usage_page ,
Nm hid_parse_usage_in_page ,
Nm hid_init ,
Nm hid_get_data ,
Nm hid_set_data
Nd USB HID access routines
Sh LIBRARY
Lb libusbhid
Sh SYNOPSIS
In usbhid.h
Ft report_desc_t
Fn hid_get_report_desc "int file"
Ft report_desc_t
Fn hid_use_report_desc "const uint8_t *data" "unsigned int size"
Ft void
Fn hid_dispose_report_desc "report_desc_t d"
Ft hid_data_t
Fn hid_start_parse "report_desc_t d" "int kindset" "int id"
Ft void
Fn hid_end_parse "hid_data_t s"
Ft int
Fn hid_get_item "hid_data_t s" "hid_item_t *h"
Ft int
Fn hid_report_size "report_desc_t d" "hid_kind_t k" "int id"
Ft int
Fn hid_locate "report_desc_t d" "u_int usage" "hid_kind_t k" "hid_item_t *h" "int id"
Ft char *
Fn hid_usage_page "int i"
Ft char *
Fn hid_usage_in_page "u_int u"
Ft int
Fn hid_parse_usage_page "const char *"
Ft int
Fn hid_parse_usage_in_page "const char *"
Ft void
Fn hid_init "const char *file"
Ft int
Fn hid_get_data "const void *data" "const hid_item_t *h"
Ft void
Fn hid_set_data "void *data" "const hid_item_t *h" "u_int data"
Sh DESCRIPTION
The
Nm
library provides routines to extract data from USB Human Interface Devices.
Ss INTRODUCTION
USB HID devices send and receive data laid out in a device dependent way.
The
Nm
library contains routines to extract the
Em report descriptor
which contains the data layout information and then use this information.
Pp
The routines can be divided into four parts: extraction of the descriptor,
parsing of the descriptor, translating to/from symbolic names, and
data manipulation.
Ss DESCRIPTOR FUNCTIONS
A report descriptor can be obtained by calling
Fn hid_get_report_desc
with a file descriptor obtained by opening a
Xr uhid 4
device.
Alternatively a data buffer containing the report descriptor can be
passed into
Fn 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
Fn hid_dispose_report_desc .
The type
Fa report_desc_t
is opaque and should be used when calling the parsing functions.
If
Fn hid_dispose_report_desc
fails it will return
Fa NULL .
Ss DESCRIPTOR PARSING FUNCTIONS
To parse the report descriptor the
Fn 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
Fa "(1 << k)"
where
Fa k
is an item of type
Fa hid_kind_t .
The report ID (if present) is given by
Fa id .
The function returns
Fa NULL
if the initialization fails, otherwise an opaque value to be used
in subsequent calls.
After parsing the
Fn hid_end_parse
function should be called to free internal data structures.
Pp
To iterate through all the items in the report descriptor,
Fn 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
Fa h
will be filled with the relevant data for the item.
The definition of
Fa hid_item_t
can be found in
In usbhid.h
and the meaning of the components in the USB HID documentation.
Pp
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
Fn hid_report_size
function.
If the report is prefixed by an ID byte it is given by
Fa id .
Pp
To locate a single item the
Fn 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.
Ss NAME TRANSLATION FUNCTIONS
The function
Fn hid_usage_page
will return the symbolic name of a usage page, and the function
Fn 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.
Pp
The functions
Fn hid_parse_usage_page
and
Fn hid_parse_usage_in_page
are the inverses of
Fn hid_usage_page
and
Fn hid_usage_in_page .
They take a usage string and return the number of the usage, or -1
if it cannot be found.
Pp
Before any of these functions can be called the usage table
must be parsed, this is done by calling
Fn hid_init
with the name of the table.
Passing
Fa NULL
to this function will cause it to use the default table.
Ss DATA EXTRACTION FUNCTIONS
Given the data obtained from a HID device and an item in the
report descriptor the
Fn hid_get_data
function extracts the value of the item.
Conversely
Fn hid_set_data
can be used to put data into a report (which must be zeroed first).
Sh FILES
Pa /usr/share/misc/usb_hid_usages
The default HID usage table.
\" .Sh EXAMPLES
Sh SEE ALSO
Xr uhid 4 ,
Xr usb 4
Pp
Lk http://www.usb.org/developers/docs/ "USB Specifications"
Sh HISTORY
The
Nm
library first appeared in
Nx 1.5
as
Nm usb
library
and was renamed to
Nm
for
Nx 1.6 .
Sh BUGS
This man page is woefully incomplete.

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