patch-2.4.10 linux/Documentation/usb/hiddev.txt

• Lines: 163
• Date: Wed Sep 12 15:34:06 2001
• Orig file: v2.4.9/linux/Documentation/usb/hiddev.txt
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.9/linux/Documentation/usb/hiddev.txt linux/Documentation/usb/hiddev.txt
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+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 disparite requirements, the Linux USB system provides
+HID events to two seperate 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.txt
+* 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.c  ----> 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 http://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.
+
+
+read():
+This is the event interface. When the HID device performs an
+interrupt transfer, indicating a change of state, data will be made
+available at the associated hiddev device with the content of 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. 
+
+
+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. 
+
+HIDIOCGDEVINFO - struct hiddev_devinfo (read)
+Gets a hiddev_devinfo structure which describes the device.
+
+HIDIOCGSTRING - struct 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.
+
+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 beforesending 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 infomation associated with this
+usage if it is found. 
+
+HIDIOCSUSAGE - struct hiddev_usage_ref (write)
+Sets the value of a usage in an output report.
+
+