252 строки
9.1 KiB
ReStructuredText
252 строки
9.1 KiB
ReStructuredText
================================================
|
|
Care and feeding of your Human Interface Devices
|
|
================================================
|
|
|
|
Introduction
|
|
============
|
|
|
|
In addition to the normal input type HID devices, USB also uses the
|
|
human interface device protocols for things that are not really human
|
|
interfaces, but have similar sorts of communication needs. The two big
|
|
examples for this are power devices (especially uninterruptable power
|
|
supplies) and monitor control on higher end monitors.
|
|
|
|
To support these disparate requirements, the Linux USB system provides
|
|
HID events to two separate interfaces:
|
|
* the input subsystem, which converts HID events into normal input
|
|
device interfaces (such as keyboard, mouse and joystick) and a
|
|
normalised event interface - see Documentation/input/input.rst
|
|
* the hiddev interface, which provides fairly raw HID events
|
|
|
|
The data flow for a HID event produced by a device is something like
|
|
the following::
|
|
|
|
usb.c ---> hid-core.c ----> hid-input.c ----> [keyboard/mouse/joystick/event]
|
|
|
|
|
|
|
|
--> hiddev.c ----> POWER / MONITOR CONTROL
|
|
|
|
In addition, other subsystems (apart from USB) can potentially feed
|
|
events into the input subsystem, but these have no effect on the hid
|
|
device interface.
|
|
|
|
Using the HID Device Interface
|
|
==============================
|
|
|
|
The hiddev interface is a char interface using the normal USB major,
|
|
with the minor numbers starting at 96 and finishing at 111. Therefore,
|
|
you need the following commands::
|
|
|
|
mknod /dev/usb/hiddev0 c 180 96
|
|
mknod /dev/usb/hiddev1 c 180 97
|
|
mknod /dev/usb/hiddev2 c 180 98
|
|
mknod /dev/usb/hiddev3 c 180 99
|
|
mknod /dev/usb/hiddev4 c 180 100
|
|
mknod /dev/usb/hiddev5 c 180 101
|
|
mknod /dev/usb/hiddev6 c 180 102
|
|
mknod /dev/usb/hiddev7 c 180 103
|
|
mknod /dev/usb/hiddev8 c 180 104
|
|
mknod /dev/usb/hiddev9 c 180 105
|
|
mknod /dev/usb/hiddev10 c 180 106
|
|
mknod /dev/usb/hiddev11 c 180 107
|
|
mknod /dev/usb/hiddev12 c 180 108
|
|
mknod /dev/usb/hiddev13 c 180 109
|
|
mknod /dev/usb/hiddev14 c 180 110
|
|
mknod /dev/usb/hiddev15 c 180 111
|
|
|
|
So you point your hiddev compliant user-space program at the correct
|
|
interface for your device, and it all just works.
|
|
|
|
Assuming that you have a hiddev compliant user-space program, of
|
|
course. If you need to write one, read on.
|
|
|
|
|
|
The HIDDEV API
|
|
==============
|
|
|
|
This description should be read in conjunction with the HID
|
|
specification, freely available from https://www.usb.org, and
|
|
conveniently linked of http://www.linux-usb.org.
|
|
|
|
The hiddev API uses a read() interface, and a set of ioctl() calls.
|
|
|
|
HID devices exchange data with the host computer using data
|
|
bundles called "reports". Each report is divided into "fields",
|
|
each of which can have one or more "usages". In the hid-core,
|
|
each one of these usages has a single signed 32 bit value.
|
|
|
|
read():
|
|
-------
|
|
|
|
This is the event interface. When the HID device's state changes,
|
|
it performs an interrupt transfer containing a report which contains
|
|
the changed value. The hid-core.c module parses the report, and
|
|
returns to hiddev.c the individual usages that have changed within
|
|
the report. In its basic mode, the hiddev will make these individual
|
|
usage changes available to the reader using a struct hiddev_event::
|
|
|
|
struct hiddev_event {
|
|
unsigned hid;
|
|
signed int value;
|
|
};
|
|
|
|
containing the HID usage identifier for the status that changed, and
|
|
the value that it was changed to. Note that the structure is defined
|
|
within <linux/hiddev.h>, along with some other useful #defines and
|
|
structures. The HID usage identifier is a composite of the HID usage
|
|
page shifted to the 16 high order bits ORed with the usage code. The
|
|
behavior of the read() function can be modified using the HIDIOCSFLAG
|
|
ioctl() described below.
|
|
|
|
|
|
ioctl():
|
|
--------
|
|
|
|
This is the control interface. There are a number of controls:
|
|
|
|
HIDIOCGVERSION
|
|
- int (read)
|
|
|
|
Gets the version code out of the hiddev driver.
|
|
|
|
HIDIOCAPPLICATION
|
|
- (none)
|
|
|
|
This ioctl call returns the HID application usage associated with the
|
|
hid device. The third argument to ioctl() specifies which application
|
|
index to get. This is useful when the device has more than one
|
|
application collection. If the index is invalid (greater or equal to
|
|
the number of application collections this device has) the ioctl
|
|
returns -1. You can find out beforehand how many application
|
|
collections the device has from the num_applications field from the
|
|
hiddev_devinfo structure.
|
|
|
|
HIDIOCGCOLLECTIONINFO
|
|
- struct hiddev_collection_info (read/write)
|
|
|
|
This returns a superset of the information above, providing not only
|
|
application collections, but all the collections the device has. It
|
|
also returns the level the collection lives in the hierarchy.
|
|
The user passes in a hiddev_collection_info struct with the index
|
|
field set to the index that should be returned. The ioctl fills in
|
|
the other fields. If the index is larger than the last collection
|
|
index, the ioctl returns -1 and sets errno to -EINVAL.
|
|
|
|
HIDIOCGDEVINFO
|
|
- struct hiddev_devinfo (read)
|
|
|
|
Gets a hiddev_devinfo structure which describes the device.
|
|
|
|
HIDIOCGSTRING
|
|
- struct hiddev_string_descriptor (read/write)
|
|
|
|
Gets a string descriptor from the device. The caller must fill in the
|
|
"index" field to indicate which descriptor should be returned.
|
|
|
|
HIDIOCINITREPORT
|
|
- (none)
|
|
|
|
Instructs the kernel to retrieve all input and feature report values
|
|
from the device. At this point, all the usage structures will contain
|
|
current values for the device, and will maintain it as the device
|
|
changes. Note that the use of this ioctl is unnecessary in general,
|
|
since later kernels automatically initialize the reports from the
|
|
device at attach time.
|
|
|
|
HIDIOCGNAME
|
|
- string (variable length)
|
|
|
|
Gets the device name
|
|
|
|
HIDIOCGREPORT
|
|
- struct hiddev_report_info (write)
|
|
|
|
Instructs the kernel to get a feature or input report from the device,
|
|
in order to selectively update the usage structures (in contrast to
|
|
INITREPORT).
|
|
|
|
HIDIOCSREPORT
|
|
- struct hiddev_report_info (write)
|
|
|
|
Instructs the kernel to send a report to the device. This report can
|
|
be filled in by the user through HIDIOCSUSAGE calls (below) to fill in
|
|
individual usage values in the report before sending the report in full
|
|
to the device.
|
|
|
|
HIDIOCGREPORTINFO
|
|
- struct hiddev_report_info (read/write)
|
|
|
|
Fills in a hiddev_report_info structure for the user. The report is
|
|
looked up by type (input, output or feature) and id, so these fields
|
|
must be filled in by the user. The ID can be absolute -- the actual
|
|
report id as reported by the device -- or relative --
|
|
HID_REPORT_ID_FIRST for the first report, and (HID_REPORT_ID_NEXT |
|
|
report_id) for the next report after report_id. Without a-priori
|
|
information about report ids, the right way to use this ioctl is to
|
|
use the relative IDs above to enumerate the valid IDs. The ioctl
|
|
returns non-zero when there is no more next ID. The real report ID is
|
|
filled into the returned hiddev_report_info structure.
|
|
|
|
HIDIOCGFIELDINFO
|
|
- struct hiddev_field_info (read/write)
|
|
|
|
Returns the field information associated with a report in a
|
|
hiddev_field_info structure. The user must fill in report_id and
|
|
report_type in this structure, as above. The field_index should also
|
|
be filled in, which should be a number from 0 and maxfield-1, as
|
|
returned from a previous HIDIOCGREPORTINFO call.
|
|
|
|
HIDIOCGUCODE
|
|
- struct hiddev_usage_ref (read/write)
|
|
|
|
Returns the usage_code in a hiddev_usage_ref structure, given that
|
|
given its report type, report id, field index, and index within the
|
|
field have already been filled into the structure.
|
|
|
|
HIDIOCGUSAGE
|
|
- struct hiddev_usage_ref (read/write)
|
|
|
|
Returns the value of a usage in a hiddev_usage_ref structure. The
|
|
usage to be retrieved can be specified as above, or the user can
|
|
choose to fill in the report_type field and specify the report_id as
|
|
HID_REPORT_ID_UNKNOWN. In this case, the hiddev_usage_ref will be
|
|
filled in with the report and field information associated with this
|
|
usage if it is found.
|
|
|
|
HIDIOCSUSAGE
|
|
- struct hiddev_usage_ref (write)
|
|
|
|
Sets the value of a usage in an output report. The user fills in
|
|
the hiddev_usage_ref structure as above, but additionally fills in
|
|
the value field.
|
|
|
|
HIDIOGCOLLECTIONINDEX
|
|
- struct hiddev_usage_ref (write)
|
|
|
|
Returns the collection index associated with this usage. This
|
|
indicates where in the collection hierarchy this usage sits.
|
|
|
|
HIDIOCGFLAG
|
|
- int (read)
|
|
HIDIOCSFLAG
|
|
- int (write)
|
|
|
|
These operations respectively inspect and replace the mode flags
|
|
that influence the read() call above. The flags are as follows:
|
|
|
|
HIDDEV_FLAG_UREF
|
|
- read() calls will now return
|
|
struct hiddev_usage_ref instead of struct hiddev_event.
|
|
This is a larger structure, but in situations where the
|
|
device has more than one usage in its reports with the
|
|
same usage code, this mode serves to resolve such
|
|
ambiguity.
|
|
|
|
HIDDEV_FLAG_REPORT
|
|
- This flag can only be used in conjunction
|
|
with HIDDEV_FLAG_UREF. With this flag set, when the device
|
|
sends a report, a struct hiddev_usage_ref will be returned
|
|
to read() filled in with the report_type and report_id, but
|
|
with field_index set to FIELD_INDEX_NONE. This serves as
|
|
additional notification when the device has sent a report.
|