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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
24E.g. 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[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
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::
121
122 struct gameport {
123
124 void *port_data;
125
126A private pointer for free use in the gameport driver. (Not the joystick
127driver!)
128
129::
130
131 char name[32];
132
133Driver's name as set by driver calling gameport_set_name(). Informational
134purpose only.
135
136::
137
138 char phys[32];
139
140gameport's physical name/description as set by driver calling gameport_set_phys().
141Informational purpose only.
142
143::
144
145 int io;
146
147I/O address for use with raw mode. You have to either set this, or ->read()
148to some value if your gameport supports raw mode.
149
150::
151
152 int speed;
153
154Raw mode speed of the gameport reads in thousands of reads per second.
155
156::
157
158 int fuzz;
159
160If the gameport supports cooked mode, this should be set to a value that
161represents the amount of noise in the data. See
162:ref:`gameport_pgm_cooked_mode`.
163
164::
165
166 void (*trigger)(struct gameport *);
167
168Trigger. This function should trigger the ns558 oneshots. If set to NULL,
169outb(0xff, io) will be used.
170
171::
172
173 unsigned char (*read)(struct gameport *);
174
175Read the buttons and ns558 oneshot bits. If set to NULL, inb(io) will be
176used instead.
177
178::
179
180 int (*cooked_read)(struct gameport *, int *axes, int *buttons);
181
182If the gameport supports cooked mode, it should point this to its cooked
183read function. It should fill axes[0..3] with four values of the joystick axes
184and buttons[0] with four bits representing the buttons.
185
186::
187
188 int (*calibrate)(struct gameport *, int *axes, int *max);
189
190Function for calibrating the ADC hardware. When called, axes[0..3] should be
191pre-filled by cooked data by the caller, max[0..3] should be pre-filled with
192expected maximums for each axis. The calibrate() function should set the
193sensitivity of the ADC hardware so that the maximums fit in its range and
194recompute the axes[] values to match the new sensitivity or re-read them from
195the hardware so that they give valid values.
196
197::
198
199 int (*open)(struct gameport *, int mode);
200
201Open() serves two purposes. First a driver either opens the port in raw or
202in cooked mode, the open() callback can decide which modes are supported.
203Second, resource allocation can happen here. The port can also be enabled
204here. Prior to this call, other fields of the gameport struct (namely the io
205member) need not to be valid.
206
207::
208
209 void (*close)(struct gameport *);
210
211Close() should free the resources allocated by open, possibly disabling the
212gameport.
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
227For internal use by the gameport layer.
228
229::
230
231 };
232
233Enjoy!