mod_mce

mod_mce

Linux input module to use Microsoft^® Remote Keyboard for Windows XP^® Media Center Edition and the matching receiver as a keyboard and mouse replacement.

Technical Background

The data from the keyboard is transferred via infrared (IR) light. Therefore the infrared light is pulsed at a high frequency (usually round about 35 kHz). The receiver takes notice of that light and measures the time, it is received. It also measures the time, it does not receive infrared light. In this case, the digital information is encapsulated in the relation between on- and off-times.

IR timing parameters used

RC6 - Media Keys

First, a synchronisation pulse of 2600µs to 3300µs is sent. Following that pulse, pulses and spaces of either 350µs to 600µs, 750µs to 1000µs or 1200µs to 1600µs are used. Each of these possible length is given a logical length of 1, 2 or 3. The sync has a logical length of 6. With this information, a series of zeroes (for spaces) and ones (for pulses) can be built. Due to limitations of the receiver used, the final space is missing and should be substituded. Here is an example of the green start key pressed:

111111 00 10 10 10 01 0011 10 01 01 01 01 01 01 01 01 01 01 01 10 10 10 10 01 01 01 01 01 10 01 01 01 01 01 01 10 10 01 10

A combination of two states gives us the final digital data. Whenever a combination 01 is seen, it results in a 0; 10 results in 1. All other pairs are not allowed. Be aware of the header consisting of the sync pulse (length 6), a space of length 2 and four bits followed by the so called 'toggle bit' -- in this case consisting of 0011 (i.e. double length). The four bits in header do not carry important information for this case. They can be used to identify the data packet, since possibly other remote controls use this kind of code, which could lead into confusion.

The final decoding of our above mentioned packet (omiting the section from sync to toggle) gives us:

1000 0000 0000 1111 0000 0100 0000 1101

The most significant bit (MSB) comes first. See below for information on the content of those data packets.

RC5 - Keyboard and Mouse

Basically the same technique as for the media keys is used. We have a sync pulse of 2600µs to 3300µs and pulse lengths of 150µs to 450µs or 500µs to 750µs, which are somewhat faster than for the media keys. Here, no toggle bits or long spaces are used. Beside the content, the data for mouse and keyboard differ in length. Some information shows up the possibility that a japanese keyboard exists with different timing.

Data Payload

The information presented here is mostly derived from recording IR data and is incomplete and highly subjective.

Media Keys

The layout is as follows


Identification				C	Code Set	Identification	Pressed Button
1000	0000	0000	1111	x	xxx	0100	xxxx	xxxx

The meaning of 'Code Set' is not known to me and is always 000 for the key strokes mentioned here. The bit 'C' seems to vary from keyboard to remote control and is not clear to me.

Value	Pressed Button
0x00	0 (rc only)
0x01	1 (rc only)
0x02	2 (rc only)
0x03	3 (rc only)
0x04	4 (rc only)
0x05	5 (rc only)
0x06	6 (rc only)
0x07	7 (rc only)
0x08	8 (rc only)
0x09	9 (rc only)
0x0A	Delete (rc only)
0x0B	Enter (rc only)
0x0C	PC Power
0x0D	Green Logo Button
0x0E	Mute
0x0F	Info
0x10	Vol +
0x11	Vol -
0x12	Ch/Pg +
0x13	Ch/Pg -
0x14	Fwd
0x15	Rew
0x16	Play
0x17	Record
0x18	Pause
0x19	Stop
0x1A	Skip
0x1B	Replay
0x1C	# (rc only)
0x1D	* (rc only)
0x1E	Up
0x1F	Down
0x20	Left
0x21	Right
0x22	OK
0x23	Back
0x24	DVD Menu
0x25	Live TV
0x26	EPG
0x46	TV (keyboard only)
0x47	Music (keyboard only)
0x48	Recorded TV
0x49	Pictures (keyboard only)
0x4A	Videos (keyboard only)
0x50	Radio (keyboard only)
0x5A	Videotext (rc only)
0x5B	Red (rc only)
0x5C	Green (rc only)
0x5D	Yellow (rc only)
0x5E	Blue (rc only)
0x64	Messenger (keyboard only)

Mouse

The data layout is as follows:

Identification		unknown		ΔY		ΔX		R	L	Checksum
0	0001	xxxx	xxxx	xxx	xxxx	xxx	xxxx	x	x	x	xxxx

The unknown bits also contain a 'code set'. The algorithm used for the checksum is not clear to me.

R is the right button flag, L is the left button flag:

Bit	Meaning
0	not pressed
1	pressed

The differences in X- and Y-direction are expressed as 7-bit signed integers in two's complement. I have not seen values less than -30 or values greater than +30. Positive X-values indicate movement to the right, positive Y-values indicate movement to the top. For completeness here the full value table (assuming the limit mentioned):

Value	Meaning
0x00	0
0x01	1
0x02	2
0x03	3
0x04	4
0x05	5
0x06	6
0x07	7
0x08	8
0x09	9
0x0A	10
0x0B	11
0x0C	12
0x0D	13
0x0E	14
0x0F	15
0x10	16
0x11	17
0x12	18
0x13	19
0x14	20
0x15	21
0x16	22
0x17	23
0x18	24
0x19	25
0x1A	26
0x1B	27
0x1C	28
0x1D	29
0x1E	30
...
0x62	-30
0x63	-29
0x64	-28
0x65	-27
0x66	-26
0x67	-25
0x68	-24
0x69	-23
0x6A	-22
0x6B	-21
0x6C	-20
0x6D	-19
0x6E	-18
0x6F	-17
0x70	-16
0x71	-15
0x72	-14
0x73	-13
0x74	-12
0x75	-11
0x76	-10
0x77	-9
0x78	-8
0x79	-7
0x7A	-6
0x7B	-5
0x7C	-4
0x7D	-3
0x7E	-2
0x7F	-1

Keyboard

The data layout is as follows:

Identification		unknown	Code Set		unknown		Key Code		Shift Mask
0	0100	xxx	x	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx

As in the other codes, the 'Code Set' is unknown to me.

The shift mask uses basically bits used also in USB HID. The following table shows the contents of 'Shift Mask'.

Bit	7	6	5	4	3	2	1	0
Key	Right Logo (n/a)	Right Alt	Right Shift	Right Ctrl	Left Logo	Left Alt	Left Shift	Left Ctrl
Matching Key Code	0xE7	0xE6	0xE5	0xE4	0xE3	0xE2	0xE1	0xE0

The right logo key is not existing on my keyboard. The bit is described only for completeness. This bit field enables the keyboard to also send key combinations like Ctrl + Alt + Delete, where Ctrl and Alt is stuffed into the shift mask.

The Key Codes also follow the USB HID standard and are described here only for reference. The assumption is made, that the keyboard is a US English keyboard (which mine is not). The keys have to be translated to your local character set. It is possible that some key codes are not sent by all keyboards, as well as some might be sent, which are not in this table.

Keycode	Meaning
0x00	All keys released (except those in Shift Mask)
0x04	A
0x05	B
0x06	C
0x07	D
0x08	E
0x09	F
0x0A	G
0x0B	H
0x0C	I
0x0D	J
0x0E	K
0x0F	L
0x10	M
0x11	N
0x12	O
0x13	P
0x14	Q
0x15	R
0x16	S
0x17	T
0x18	U
0x19	V
0x1A	W
0x1B	X
0x1C	Y
0x1D	Z
0x1E	1
0x1F	2
0x20	3
0x21	4
0x22	5
0x23	6
0x24	7
0x25	8
0x26	9
0x27	0
0x28	↵
0x29	Esc
0x2A	← (backspace)
0x2B	Tab
0x2C	Space
0x2D	-
0x2E	=
0x2F	[
0x30	]
0x31	\
0x32	Non-US #
0x33	;
0x34	'
0x35	`
0x36	,
0x37	.
0x38	/
0x39	Caps Lock
0x3A	F1
0x3B	F2
0x3C	F3
0x3D	F4
0x3E	F5
0x3F	F6
0x40	F7
0x41	F8
0x42	F9
0x43	F10
0x44	F11
0x45	F12
0x46	Print Screen
0x47	Scroll Lock
0x48	Pause
0x49	Insert
0x4A	Home
0x4B	Page Up
0x4C	Delete
0x4D	End
0x4E	Page Down
0x4F	→
0x50	←
0x51	↓
0x52	↑
...
0x64	Non-US \
0x65	Application (=context menu)
...

Available Source Code

mod_mce

Since some new input functions are used in this project, please update your kernel. You have to enable USB and input in your kernel configuration. Building is done by executing 'make'.

mce_lircd

This is a daemon for those without the USB receiver but with a lirc-compatible receiver. This daemon relies on user input to be activated in your kernel.

lirc_mod_mce

Due to popular demand, I quickly assembled this driver which is basically a combination of mod_mce and a lirc module. This driver allows you to use the keyboard/mouse features as well as the remote control features at the same time.

lircd.conf

This config file can be used for the media keys. At the moment you can use either lirc or one of mod_mce or mce_lircd. It can be downloaded here.

Since the project is in some early stage, I unfortunately cannot give you more assistance right now.

For further information take a look at the SourceForge files page.

Contact

If you feel to contact me, please first take a look at the SourceForge page and check if the issue has been previously posted.

Last revision: 2006-09-06