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3. Getting your mouse working.

Once you have figured out your mouse interface and protocol types, you're ready to proceed.

3.1 Setting the mouse interrupt.

Now that you've found out what hardware interface your mouse uses you'll need to know which interrupt number your mouse is using, and make sure it doesn't conflict with any other peripherals you have installed. That last part deserves to be repeated! Make sure that it does not conflict with any other peripherals you have installed!

You should make sure that your mouse is not trying to use the same interrupt as any of your other devices --- it is not possible for the mouse to share an interrupt under Linux, even though it may work fine under other operating systems. Check the documentation for all your peripherals to see which interrupt they use.

Under Linux, busmice don't register which IRQ they are using until after they have been opened by an application that makes use of them. Plug-n-Play hardware often registers their interrupts during bootup. This creates a possibility for a Plug-n-Play peice of hardware to steal the IRQ away from your mouse. Bear in mind that other operating systems may be initialzing the P-n-P cards to an IRQ that is not in conflict with your busmouse but things may not work out as nicely under Linux. It is up to you to make sure there are no IRQ conflicts between all of your equipment.

Common IRQ usage.In most cases IRQ4 is used for the first serial port (/dev/ttyS0),IRQ3 for the second (/dev/ttyS1) (these are assuming youactually have such devices --- if you don't you can happily usetheir IRQ's), IRQ5 for some SCSI adaptors, and IRQ12 for some network cards.Having a other card use IRQ12 is a big problem for machines with PS/2 ports asyou are forced to use IRQ12 only for the PS/2 port.For ATI-XL, Inport and Logitech mice the kerneldefault is to use IRQ5, so if you are stuck with a pre-compiledkernel (eg, CD-ROM users) you will have to use that. If you areusing an Inport or Logitech mice with a newer kernel you may be able topass a command line option to the kernel to tell it what interruptto use without recompiling.

Inport and Logitech mice.

If you open up your computer's case and look at the card which your mouse plugs into, you should notice a block of jumpers on the card (hopefully labeled ``INTERRUPT'') with positions for interrupt (otherwise known as IRQ) numbers 2,3,4 and 5. To change the interrupt simply move the jumper from its current position onto the correct pair of pins.

***     MAKE SURE YOUR COMPUTER IS TURNED OFF   ***
***     BEFORE CHANGING THE JUMPERS AROUND!!    ***

ATI-XL mice.

ATI-XL and a few other ATI busmice have a software selectable IRQ - you should have received with your mouse a MS-DOS program (VSETUP.EXE) to set the IRQ. In order to do so you must (temporarily) boot MS-DOS and run this program. Note that the VSETUP program takes an optional parameter ``/70'' to increase the vertical refresh rate (which results in less flicker). The VSETUP program also allows you to select either the primary or secondary mouse address - you should set this to the primary address or the kernel will not be able to detect your mouse.

Once VSETUP has been run you must perform a hard reset for the new configuration to take effect.

PS/2 mice.

The PS/2 mouse always uses IRQ12 -- there is no way of changing this (except with a soldering gun.) In the rare case that some other device is using IRQ12, you'll have to rejumper that peripheral to use another IRQ number.

3.2 Configuring the kernel.

In order for your busmouse to operate correctly you will need to configure your kernel to compile in busmouse support. If you are using a pre-compiled kernel then it often comes with support for all three busmouse included. This may still not be enough. The kernel could be trying to use the wrong interrupt or the detection can get confused and treat your mouse as the wrong type.

In pre-2.4 series kernel there is no support for auto-detection of the IRQ that a busmouse is using. Therefore, if your card is set to anything but the kernel default value of IRQ 5 then you will need to let the kernel know what IRQ to use instead. This can be done in one of two ways. The easiest is to pass command line options to the kernel during the bootup process. Please read thru the "Compiling the kernel" section for reference but attempt the directions in "Changing interrupts with newer kernels" first. Also of great help in this area is the Bootprompt-HOWTO, avaliable at most sites that carry this HOWTO.

Compiling the kernel.

Change to your kernel directory (here assumed to be (/usr/src/linux) and do a

make config

If you are unsure as to your mouse type, the first time you recompile the kernel you may wish to enable all of the busmouse options in the hope that the kernel will autodetect your mouse properly. People have mixed success with this: it doesn't always work, but on the other hand it might save you any further compiles.

Answer ``y'' or ''m'' to the question pertaining to your type of busmouse interface and ``n'' to all the other busmouse questions. Use the ''m'' option if you have your system setup to support loading kernel modules if you do not or do not know what that means then it will be safe to always answer ''y'' to have the support directly compiled into your kernel.

As an example, if you have an Inport mouse you should answer ``y'' to

Microsoft busmouse support

and ``n'' to all other busmouse questions. Answer the non-mouse related questions as you usually would.

To compile the kernel with PS/2 mouse support answer ``y'' to the question.

PS/2 mouse (aka "auxiliary device") support

The PS/2 mouse driver actually supports two kinds of devices: the standard PS/2 Auxiliary Device controller and a special PS/2 mouse interface chip from Chips & Technologies which is used in the Texas Instruments Travelmate and Gateway Nomad laptops. To compile in support for the trackballs on these computers, answer ``y'' to the

C&T 82C710 mouse port support (as on TI Travelmate)

question. Note that you will still have to answer ``y'' to the question about the standard PS/2 driver to even get a chance to answer this question, since the 82C710 driver is actually an add-on to the standard PS/2 mouse driver.

When configured both for a standard PS/2 mouse device and the 82C710 device, the driver first tries to locate a 82C710 chip at boot time. Failing this, the standard driver is used instead, so using a kernel configured for both types of interface on a machine with a standard PS/2 mouse port should work too. However, there has been one report of a falsely detected 82C710 chip, so to be on the safe side do not configure in support for the 82C710 if you don't need it.

You will now need to tell the kernel what interrupt your mouse uses. You can skip this step if your using a PS/2 mouse as it always uses IRQ 12.

If you have a Logitech, Inport mouse, or an ATI mouse that uses the Logitech protocol, edit the file /usr/src/linux/include/linux/busmouse.h and change the line which says

#define MOUSE_IRQ 5

to reflect the interrupt number for your mouse (see the section Setting the mouse interrupt for details on finding your interrupt number).

If you have an ATI-XL mouse, edit the file /usr/src/linux/drivers/char/atixlmouse.c and change the line which says

#define ATIXL_MOUSE_IRQ 5

to reflect your mouse's interrupt number.

Due to the vagaries of the PC architecture, if you have set your mouse to use interrupt 2, you must set the #define to use interrupt 9.

Examples

For a mouse on interrupt 3, you should change the line to read

#define MOUSE_IRQ 3

For a mouse on interrupt 2, you should change the line to read

#define MOUSE_IRQ 9

Next, compile your kernel as per the instructions which come with it, and boot from the new kernel. You should now have the busmouse support correctly compiled in.

Changing interrupts with newer kernels.

The steps to compile into the kernel what interrupt it uses works with any version of the kernel to date. Newer kernels (starting somewhere in the 2.x.x's) allow you to pass arguments to the kernel during load time using something like LILO or LOADLIN to specify the interrupt number for Logitech and Microsoft Inport mice. This can be a real time saver as you do not need to recompiler your kernel (or know how to). If you've configured your kernel to load the mouse drivers as modules then you will need to pass this information when loading the module.

You can add the following options to your boot line in LILO to change interrupt:

bmouse=3  (Logitech Busmice)
msmouse=3 (for Microsoft Inport mice)

Substitute the 3 with your mouse's actual interrupt. An example of using this with lilo is:

LILO:linux msmouse=3

You can consult your LILO or LOADLIN docs to see how to add this type information to their configuration files so that you do not need to type it.

If your system uses kerneld to auto load modules, you can edit your /etc/conf.modules or /etc/modules.conf file, which ever your system uses, and add one of the following lines.

options msbusmouse mouse_irq=3
options busmouse mouse_irq=3

3.3 The mouse devices.

Mice under Linux are accessed via the devices in the /dev directory. The following table gives a list of interface types and which device you should use.

INTERFACE        DEVICE        MAJOR    MINOR
---------------------------------------------
Logitech        /dev/logibm      10      0
PS/2            /dev/psaux       10      1
Inport          /dev/inportbm    10      2
ATI-XL          /dev/atibm       10      3

Note: If you are using your ATI-XL mouse with the Inport driver, you should use the inportbm device, not the /dev/atibm device.

The major and minor entries are the device numbers for that particular device.

If you find that you do not have these devices, you should create them first. To do so, execute the following as root.

mknod /dev/logimm    c 10 0
mknod /dev/psaux     c 10 1
mknod /dev/inportbm  c 10 2
mknod /dev/atibm     c 10 3

Note: Some time in the (progressively less) recent history of Linux the names for the busmouse devices have changed. The following device names have been superceded by those above and should be removed: bmousems, bmouseps2, bmouseatixl, and bmouselogitech..

Many people like to create a symbolic link from their mouse device to /dev/mouse so that they don't have to remember which device they need to be using. If you have one of the current Linux distributions you will almost certainly find that you have such a link. If you have such a link, or create one, you should make sure that it is pointing to the correct device for your mouse.


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