I am not familiar with your desired final product but I would mention that joysticks
usually have resistive potentiometers and therefore could be used to feed the input to
an ADC board. This would probably get around some of the hardware/driver issues
associated with the inexpensive I/O architecture of the game port. Obviously, this
reduces the generic PC portability and increases the complexity.
I wonder how using the game port differs from the same joystick with USB? Anyone?
Just a thought,
Rich
> ----------
> From: [EMAIL PROTECTED][SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, May 31, 2000 10:04 AM
> To: Andrew Price
> Cc: Tomasz Motylewski; [EMAIL PROTECTED]
> Subject: Re: [rtl] RTLinux and joystick
>
> On Wed, May 31, 2000 at 02:56:56PM +1000, Andrew Price wrote:
> > I ran a very small real time application whose sole purpose was to
> > toggle
> > a bit of the parallel port every 100us.
> >
> > In the long term I will use this to schedule events etc etc..
> >
> > The application I am working on also has need for the joystick.
> >
> > When I ran up the current joystick driver for linux, and in particular
> > the
> > joystick driver for the microsoft (cringe) sidewinder it caused the
> > system
> > to lock up. If I slowed the rate of the real time process. to one toggle
> > every 2ms
> > the joystick operates normally.
> >
> >
> > I used the example program for latency testing for the parallel port
> > along with
> > 'jstest' an example that is packaged with the current joystick driver
> > for linux.
> >
> >
> > Can anyone explain why the high rate of the real time process affects
> > what the joystick,
> > a common garden variety process is doing?
>
> A quick look at the sidewinder driver shows this amusing comment:
>
> /*
> * js_sw_read_packet() is a function which reads either a data packet, or an
> * identification packet from a SideWinder joystick. Better don't try to
> * understand this, since all the ugliness of the Microsoft Digital
> * Overdrive protocol is concentrated in this function. If you really want
> * to know how this works, first go watch a couple horror movies, so that
> * you are well prepared, read US patent #5628686 and then e-mail me,
> * and I'll send you an explanation.
> * Vojtech <[EMAIL PROTECTED]>
> */
>
>
> and then this cli protected code:
> do {
> bitout--;
> u = v;
> v = inb(io);
> } while (!(~v & u & 0x10) && (bitout > 0)); /* Wait for first
>falling edge on clock */
>
> So it tries to turn off interrupts and do a busy wait for a falling edge. I bet these
> last for near millisecond periods -- with a 100us RT thread interrupting the device
> is not going to work well at all.
>
> Sorry. One solution is to get a better joystick. Another is to run on a SMP board.
>
>
>
>
> --
> ---------------------------------------------------------
> Victor Yodaiken
> FSMLabs: www.fsmlabs.com www.rtlinux.com
> FSMLabs is a servicemark and a service of
> VJY Associates L.L.C, New Mexico.
>
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