path: root/lib/libusbhid/usbhid.3

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.Dd $Mdocdate: May 12 2020 $
.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_start ,
.Nm hid_init ,
.Nm hid_get_data ,
.Nm hid_set_data
.Nd USB HID access routines
.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 "unsigned char *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 const char *
.Fn hid_usage_page "int i"
.Ft const 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 "char *file"
.Ft int
.Fn hid_start "char *file"
.Ft int32_t
.Fn hid_get_data "void *data" "hid_item_t *h"
.Ft void
.Fn hid_set_data "void *data" "hid_item_t *h" "int32_t 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.
.Fn hid_get_report_desc
and
.Fn hid_use_report_desc
return
.Fa NULL
on failure.
.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 desired report ID, or \-1
to obtain items of all report IDs,
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_start
with the name of the table.
Passing
.Fa NULL
to this function will cause it to use the default table.
A return value of \-1 indicates that an error has occurred, and
.Va errno
is set.
.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
The USB specifications can be found at:
.Lk https://www.usb.org/documents/
.Pp
.Xr uhid 4 ,
.Xr usb 4
.Sh HISTORY
The
.Nm
library first appeared in
.Ox 3.0 .
.Sh BUGS
This man page is woefully incomplete.