223 lines
6 KiB
ReStructuredText
Executable file
223 lines
6 KiB
ReStructuredText
Executable file
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Programming gameport drivers
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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A basic classic gameport
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~~~~~~~~~~~~~~~~~~~~~~~~
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If the gameport doesn't provide more than the inb()/outb() functionality,
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the code needed to register it with the joystick drivers is simple::
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struct gameport gameport;
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gameport.io = MY_IO_ADDRESS;
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gameport_register_port(&gameport);
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Make sure struct gameport is initialized to 0 in all other fields. The
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gameport generic code will take care of the rest.
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If your hardware supports more than one io address, and your driver can
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choose which one to program the hardware to, starting from the more exotic
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addresses is preferred, because the likelihood of clashing with the standard
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0x201 address is smaller.
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Eg. if your driver supports addresses 0x200, 0x208, 0x210 and 0x218, then
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0x218 would be the address of first choice.
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If your hardware supports a gameport address that is not mapped to ISA io
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space (is above 0x1000), use that one, and don't map the ISA mirror.
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Also, always request_region() on the whole io space occupied by the
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gameport. Although only one ioport is really used, the gameport usually
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occupies from one to sixteen addresses in the io space.
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Please also consider enabling the gameport on the card in the ->open()
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callback if the io is mapped to ISA space - this way it'll occupy the io
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space only when something really is using it. Disable it again in the
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->close() callback. You also can select the io address in the ->open()
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callback, so that it doesn't fail if some of the possible addresses are
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already occupied by other gameports.
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Memory mapped gameport
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~~~~~~~~~~~~~~~~~~~~~~
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When a gameport can be accessed through MMIO, this way is preferred, because
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it is faster, allowing more reads per second. Registering such a gameport
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isn't as easy as a basic IO one, but not so much complex::
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struct gameport gameport;
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void my_trigger(struct gameport *gameport)
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{
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my_mmio = 0xff;
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}
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unsigned char my_read(struct gameport *gameport)
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{
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return my_mmio;
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}
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gameport.read = my_read;
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gameport.trigger = my_trigger;
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gameport_register_port(&gameport);
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.. _gameport_pgm_cooked_mode:
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Cooked mode gameport
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~~~~~~~~~~~~~~~~~~~~
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There are gameports that can report the axis values as numbers, that means
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the driver doesn't have to measure them the old way - an ADC is built into
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the gameport. To register a cooked gameport::
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struct gameport gameport;
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int my_cooked_read(struct gameport *gameport, int *axes, int *buttons)
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{
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int i;
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for (i = 0; i < 4; i++)
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axes[i] = my_mmio[i];
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buttons[i] = my_mmio[4];
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}
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int my_open(struct gameport *gameport, int mode)
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{
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return -(mode != GAMEPORT_MODE_COOKED);
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}
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gameport.cooked_read = my_cooked_read;
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gameport.open = my_open;
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gameport.fuzz = 8;
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gameport_register_port(&gameport);
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The only confusing thing here is the fuzz value. Best determined by
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experimentation, it is the amount of noise in the ADC data. Perfect
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gameports can set this to zero, most common have fuzz between 8 and 32.
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See analog.c and input.c for handling of fuzz - the fuzz value determines
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the size of a gaussian filter window that is used to eliminate the noise
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in the data.
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More complex gameports
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~~~~~~~~~~~~~~~~~~~~~~
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Gameports can support both raw and cooked modes. In that case combine either
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examples 1+2 or 1+3. Gameports can support internal calibration - see below,
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and also lightning.c and analog.c on how that works. If your driver supports
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more than one gameport instance simultaneously, use the ->private member of
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the gameport struct to point to your data.
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Unregistering a gameport
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~~~~~~~~~~~~~~~~~~~~~~~~
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Simple::
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gameport_unregister_port(&gameport);
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The gameport structure
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~~~~~~~~~~~~~~~~~~~~~~
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.. note::
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This section is outdated. There are several fields here that don't
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match what's there at include/linux/gameport.h.
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::
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struct gameport {
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void *private;
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A private pointer for free use in the gameport driver. (Not the joystick
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driver!)
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::
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int number;
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Number assigned to the gameport when registered. Informational purpose only.
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::
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int io;
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I/O address for use with raw mode. You have to either set this, or ->read()
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to some value if your gameport supports raw mode.
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::
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int speed;
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Raw mode speed of the gameport reads in thousands of reads per second.
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::
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int fuzz;
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If the gameport supports cooked mode, this should be set to a value that
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represents the amount of noise in the data. See
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:ref:`gameport_pgm_cooked_mode`.
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::
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void (*trigger)(struct gameport *);
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Trigger. This function should trigger the ns558 oneshots. If set to NULL,
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outb(0xff, io) will be used.
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::
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unsigned char (*read)(struct gameport *);
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Read the buttons and ns558 oneshot bits. If set to NULL, inb(io) will be
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used instead.
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::
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int (*cooked_read)(struct gameport *, int *axes, int *buttons);
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If the gameport supports cooked mode, it should point this to its cooked
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read function. It should fill axes[0..3] with four values of the joystick axes
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and buttons[0] with four bits representing the buttons.
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::
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int (*calibrate)(struct gameport *, int *axes, int *max);
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Function for calibrating the ADC hardware. When called, axes[0..3] should be
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pre-filled by cooked data by the caller, max[0..3] should be pre-filled with
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expected maximums for each axis. The calibrate() function should set the
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sensitivity of the ADC hardware so that the maximums fit in its range and
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recompute the axes[] values to match the new sensitivity or re-read them from
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the hardware so that they give valid values.
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::
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int (*open)(struct gameport *, int mode);
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Open() serves two purposes. First a driver either opens the port in raw or
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in cooked mode, the open() callback can decide which modes are supported.
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Second, resource allocation can happen here. The port can also be enabled
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here. Prior to this call, other fields of the gameport struct (namely the io
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member) need not to be valid.
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::
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void (*close)(struct gameport *);
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Close() should free the resources allocated by open, possibly disabling the
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gameport.
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::
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struct gameport_dev *dev;
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struct gameport *next;
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For internal use by the gameport layer.
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::
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};
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Enjoy!
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