A picture of Blaise Gassend
The Intellimouse Protocol

Here is a description of the intellimouse protocol that I wrote up a while ago. An excellent page for mouse protocols can be found here also.

If you want info about imps2, here is what I have. It is straight out of the XFree sources, I have used it many times and it seems reliable :

To initialize a mouse in imps2 mode, you send it 243, 200, 243, 100, 243, 80. Before that you have to initialize it as a PS2 mouse, though.

The packet format is 4 bytes :

Byte 0:

Bit Contents
0 Left button
1 Right button
2 Middle button
3 Nothing? always 1
4 X bit 8
5 Y bit 8
6 Button 4 (untested) other sources say X overflow
7 Button 5 (untested) other sources say Y overflow

Note that GPM currently expects buttons 4 and 5 to be unpressed or it will discard the packet. I have never personally seen a mouse that has these buttons.

Byte 1:

X bits 7 to 0 X is calculated by :

if (byte[0] & 0x10) byte[1] else byte[1] - 256;

Byte 2:

Y bits 7 to 0

Y is given by if (byte[0] & 0x20) -byte[2] else 256 - byte[2];

Byte 3:

Z Axis (the roller).

Indicates how much the roller has moved. I have never seen values other than -1 and +1 on a standard intellimouse. On my trust intellimouse with two rollers, I seem to remember that the second roller sends -2 and +2 in this field.