1 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 Programming gameport drivers
3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4
5 A basic classic gameport
6 ~~~~~~~~~~~~~~~~~~~~~~~~
7
8 If the gameport doesn't provide more than the inb()/outb() functionality,
9 the 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
16 Make sure struct gameport is initialized to 0 in all other fields. The
17 gameport generic code will take care of the rest.
18
19 If your hardware supports more than one io address, and your driver can
20 choose which one to program the hardware to, starting from the more exotic
21 addresses is preferred, because the likelihood of clashing with the standard
22 0x201 address is smaller.
23
24 E.g. if your driver supports addresses 0x200, 0x208, 0x210 and 0x218, then
25 0x218 would be the address of first choice.
26
27 If your hardware supports a gameport address that is not mapped to ISA io
28 space (is above 0x1000), use that one, and don't map the ISA mirror.
29
30 Also, always request_region() on the whole io space occupied by the
31 gameport. Although only one ioport is really used, the gameport usually
32 occupies from one to sixteen addresses in the io space.
33
34 Please also consider enabling the gameport on the card in the ->open()
35 callback if the io is mapped to ISA space - this way it'll occupy the io
36 space 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()
38 callback, so that it doesn't fail if some of the possible addresses are
39 already occupied by other gameports.
40
41 Memory mapped gameport
42 ~~~~~~~~~~~~~~~~~~~~~~
43
44 When a gameport can be accessed through MMIO, this way is preferred, because
45 it is faster, allowing more reads per second. Registering such a gameport
46 isn'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
66 Cooked mode gameport
67 ~~~~~~~~~~~~~~~~~~~~
68
69 There are gameports that can report the axis values as numbers, that means
70 the driver doesn't have to measure them the old way - an ADC is built into
71 the 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[0] = 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
94 The only confusing thing here is the fuzz value. Best determined by
95 experimentation, it is the amount of noise in the ADC data. Perfect
96 gameports can set this to zero, most common have fuzz between 8 and 32.
97 See analog.c and input.c for handling of fuzz - the fuzz value determines
98 the size of a gaussian filter window that is used to eliminate the noise
99 in the data.
100
101 More complex gameports
102 ~~~~~~~~~~~~~~~~~~~~~~
103
104 Gameports can support both raw and cooked modes. In that case combine either
105 examples 1+2 or 1+3. Gameports can support internal calibration - see below,
106 and also lightning.c and analog.c on how that works. If your driver supports
107 more than one gameport instance simultaneously, use the ->private member of
108 the gameport struct to point to your data.
109
110 Unregistering a gameport
111 ~~~~~~~~~~~~~~~~~~~~~~~~
112
113 Simple::
114
115 gameport_unregister_port(&gameport);
116
117 The gameport structure
118 ~~~~~~~~~~~~~~~~~~~~~~
119
120 ::
121
122 struct gameport {
123
124 void *port_data;
125
126 A private pointer for free use in the gameport driver. (Not the joystick
127 driver!)
128
129 ::
130
131 char name[32];
132
133 Driver's name as set by driver calling gameport_set_name(). Informational
134 purpose only.
135
136 ::
137
138 char phys[32];
139
140 gameport's physical name/description as set by driver calling gameport_set_phys().
141 Informational purpose only.
142
143 ::
144
145 int io;
146
147 I/O address for use with raw mode. You have to either set this, or ->read()
148 to some value if your gameport supports raw mode.
149
150 ::
151
152 int speed;
153
154 Raw mode speed of the gameport reads in thousands of reads per second.
155
156 ::
157
158 int fuzz;
159
160 If the gameport supports cooked mode, this should be set to a value that
161 represents the amount of noise in the data. See
162 :ref:`gameport_pgm_cooked_mode`.
163
164 ::
165
166 void (*trigger)(struct gameport *);
167
168 Trigger. This function should trigger the ns558 oneshots. If set to NULL,
169 outb(0xff, io) will be used.
170
171 ::
172
173 unsigned char (*read)(struct gameport *);
174
175 Read the buttons and ns558 oneshot bits. If set to NULL, inb(io) will be
176 used instead.
177
178 ::
179
180 int (*cooked_read)(struct gameport *, int *axes, int *buttons);
181
182 If the gameport supports cooked mode, it should point this to its cooked
183 read function. It should fill axes[0..3] with four values of the joystick axes
184 and buttons[0] with four bits representing the buttons.
185
186 ::
187
188 int (*calibrate)(struct gameport *, int *axes, int *max);
189
190 Function for calibrating the ADC hardware. When called, axes[0..3] should be
191 pre-filled by cooked data by the caller, max[0..3] should be pre-filled with
192 expected maximums for each axis. The calibrate() function should set the
193 sensitivity of the ADC hardware so that the maximums fit in its range and
194 recompute the axes[] values to match the new sensitivity or re-read them from
195 the hardware so that they give valid values.
196
197 ::
198
199 int (*open)(struct gameport *, int mode);
200
201 Open() serves two purposes. First a driver either opens the port in raw or
202 in cooked mode, the open() callback can decide which modes are supported.
203 Second, resource allocation can happen here. The port can also be enabled
204 here. Prior to this call, other fields of the gameport struct (namely the io
205 member) need not to be valid.
206
207 ::
208
209 void (*close)(struct gameport *);
210
211 Close() should free the resources allocated by open, possibly disabling the
212 gameport.
213
214 ::
215
216 struct timer_list poll_timer;
217 unsigned int poll_interval; /* in msecs */
218 spinlock_t timer_lock;
219 unsigned int poll_cnt;
220 void (*poll_handler)(struct gameport *);
221 struct gameport *parent, *child;
222 struct gameport_driver *drv;
223 struct mutex drv_mutex; /* protects serio->drv so attributes can pin driver */
224 struct device dev;
225 struct list_head node;
226
227 For internal use by the gameport layer.
228
229 ::
230
231 };
232
233 Enjoy!
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