Dreamcast Programming

There are at least two models of mice available, the Japanese HKT-9900 and the American HKT-4200. The latter has three buttons (two on top and one thumb button) and a mouse wheel. The earlier seems to have the same set of features, but this has not yet been verified. The mouse is connected to the Maple Bus, just like other controller-type peripherals.

The current state of a mouse is queried with the Get condition request. The condition stucture for the Mouse function code ($200) is as follows:

int32 buttons       ; digital buttons bitfield (little endian)
int16 axis1         ; horizontal movement (0-$3FF) (little endian)
int16 axis2         ; vertical movement (0-$3FF) (little endian)
int16 axis3         ; mouse wheel movement (0-$3FF) (little endian)
int16 axis4         ; ? movement (0-$3FF) (little endian)
int16 axis5         ; ? movement (0-$3FF) (little endian)
int16 axis6         ; ? movement (0-$3FF) (little endian)
int16 axis7         ; ? movement (0-$3FF) (little endian)
int16 axis8         ; ? movement (0-$3FF) (little endian)

The buttons bitfield contains zeroes for pressed buttons, and ones for unpressed buttons (only the 8 least significant bits are used).

Bit	Button
0	Middle button (C)
1	Right button (B)
2	Left button (A)
3	Thumb button (START)
4	? button
5	? button
6	? button
7	? button

The axis movement fields contain the amount of movement since the last poll, as an offseted integer. $200 means no movement, $0 is maximum movement to the left / up, and $3FF is maximum movement to the right / down.

The function_data for the Mouse function code is a bitfield describing which controls are present on the particular device (zero = not present, one = present):

Bit Control

0 Axis 1

1 Axis 2

2 Axis 3

3 Axis 4

4 Axis 5

5 Axis 6

6 Axis 7

7 Axis 8

8 Middle button

9 Right button

10 Left button

11 Thumb button

12 ? button

13 ? button

14 ? button

15 ? button

Dreamcast Programming by Marcus Comstedt
Last modified: Tue Dec 12 00:09:49 MET 2000