1~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2Programming gameport drivers
3~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4
5A basic classic gameport
6~~~~~~~~~~~~~~~~~~~~~~~~
7
8If the gameport doesn't provide more than the inb()/outb() functionality,
9the code needed to register it with the joystick drivers is simple::
10
11	struct gameport gameport;
12
13	gameport.io = MY_IO_ADDRESS;
14	gameport_register_port(&gameport);
15
16Make sure struct gameport is initialized to 0 in all other fields. The
17gameport generic code will take care of the rest.
18
19If your hardware supports more than one io address, and your driver can
20choose which one to program the hardware to, starting from the more exotic
21addresses is preferred, because the likelihood of clashing with the standard
220x201 address is smaller.
23
24Eg. if your driver supports addresses 0x200, 0x208, 0x210 and 0x218, then
250x218 would be the address of first choice.
26
27If your hardware supports a gameport address that is not mapped to ISA io
28space (is above 0x1000), use that one, and don't map the ISA mirror.
29
30Also, always request_region() on the whole io space occupied by the
31gameport. Although only one ioport is really used, the gameport usually
32occupies from one to sixteen addresses in the io space.
33
34Please also consider enabling the gameport on the card in the ->open()
35callback if the io is mapped to ISA space - this way it'll occupy the io
36space only when something really is using it. Disable it again in the
37->close() callback. You also can select the io address in the ->open()
38callback, so that it doesn't fail if some of the possible addresses are
39already occupied by other gameports.
40
41Memory mapped gameport
42~~~~~~~~~~~~~~~~~~~~~~
43
44When a gameport can be accessed through MMIO, this way is preferred, because
45it is faster, allowing more reads per second. Registering such a gameport
46isn't as easy as a basic IO one, but not so much complex::
47
48	struct gameport gameport;
49
50	void my_trigger(struct gameport *gameport)
51	{
52		my_mmio = 0xff;
53	}
54
55	unsigned char my_read(struct gameport *gameport)
56	{
57		return my_mmio;
58	}
59
60	gameport.read = my_read;
61	gameport.trigger = my_trigger;
62	gameport_register_port(&gameport);
63
64.. _gameport_pgm_cooked_mode:
65
66Cooked mode gameport
67~~~~~~~~~~~~~~~~~~~~
68
69There are gameports that can report the axis values as numbers, that means
70the driver doesn't have to measure them the old way - an ADC is built into
71the gameport. To register a cooked gameport::
72
73	struct gameport gameport;
74
75	int my_cooked_read(struct gameport *gameport, int *axes, int *buttons)
76	{
77		int i;
78
79		for (i = 0; i < 4; i++)
80			axes[i] = my_mmio[i];
81		buttons[i] = my_mmio[4];
82	}
83
84	int my_open(struct gameport *gameport, int mode)
85	{
86		return -(mode != GAMEPORT_MODE_COOKED);
87	}
88
89	gameport.cooked_read = my_cooked_read;
90	gameport.open = my_open;
91	gameport.fuzz = 8;
92	gameport_register_port(&gameport);
93
94The only confusing thing here is the fuzz value. Best determined by
95experimentation, it is the amount of noise in the ADC data. Perfect
96gameports can set this to zero, most common have fuzz between 8 and 32.
97See analog.c and input.c for handling of fuzz - the fuzz value determines
98the size of a gaussian filter window that is used to eliminate the noise
99in the data.
100
101More complex gameports
102~~~~~~~~~~~~~~~~~~~~~~
103
104Gameports can support both raw and cooked modes. In that case combine either
105examples 1+2 or 1+3. Gameports can support internal calibration - see below,
106and also lightning.c and analog.c on how that works. If your driver supports
107more than one gameport instance simultaneously, use the ->private member of
108the gameport struct to point to your data.
109
110Unregistering a gameport
111~~~~~~~~~~~~~~~~~~~~~~~~
112
113Simple::
114
115    gameport_unregister_port(&gameport);
116
117The gameport structure
118~~~~~~~~~~~~~~~~~~~~~~
119
120.. note::
121
122    This section is outdated. There are several fields here that don't
123    match what's there at include/linux/gameport.h.
124
125::
126
127    struct gameport {
128
129	void *private;
130
131A private pointer for free use in the gameport driver. (Not the joystick
132driver!)
133
134::
135
136	int number;
137
138Number assigned to the gameport when registered. Informational purpose only.
139
140::
141
142	int io;
143
144I/O address for use with raw mode. You have to either set this, or ->read()
145to some value if your gameport supports raw mode.
146
147::
148
149	int speed;
150
151Raw mode speed of the gameport reads in thousands of reads per second.
152
153::
154
155	int fuzz;
156
157If the gameport supports cooked mode, this should be set to a value that
158represents the amount of noise in the data. See
159:ref:`gameport_pgm_cooked_mode`.
160
161::
162
163	void (*trigger)(struct gameport *);
164
165Trigger. This function should trigger the ns558 oneshots. If set to NULL,
166outb(0xff, io) will be used.
167
168::
169
170	unsigned char (*read)(struct gameport *);
171
172Read the buttons and ns558 oneshot bits. If set to NULL, inb(io) will be
173used instead.
174
175::
176
177	int (*cooked_read)(struct gameport *, int *axes, int *buttons);
178
179If the gameport supports cooked mode, it should point this to its cooked
180read function. It should fill axes[0..3] with four values of the joystick axes
181and buttons[0] with four bits representing the buttons.
182
183::
184
185	int (*calibrate)(struct gameport *, int *axes, int *max);
186
187Function for calibrating the ADC hardware. When called, axes[0..3] should be
188pre-filled by cooked data by the caller, max[0..3] should be pre-filled with
189expected maximums for each axis. The calibrate() function should set the
190sensitivity of the ADC hardware so that the maximums fit in its range and
191recompute the axes[] values to match the new sensitivity or re-read them from
192the hardware so that they give valid values.
193
194::
195
196	int (*open)(struct gameport *, int mode);
197
198Open() serves two purposes. First a driver either opens the port in raw or
199in cooked mode, the open() callback can decide which modes are supported.
200Second, resource allocation can happen here. The port can also be enabled
201here. Prior to this call, other fields of the gameport struct (namely the io
202member) need not to be valid.
203
204::
205
206	void (*close)(struct gameport *);
207
208Close() should free the resources allocated by open, possibly disabling the
209gameport.
210
211::
212
213	struct gameport_dev *dev;
214	struct gameport *next;
215
216For internal use by the gameport layer.
217
218::
219
220    };
221
222Enjoy!
223