On Wed, 14 Jul 1999 [EMAIL PROTECTED] wrote:
> Great to know from Don Gaffney that a joystick works with RTL 1.1 and linux
> 3.0.36 for "a real-time task to control the output of
> a DIO and an AO board in conjunction with a custom scientific
> instrument." Does this let you control devices without the intermediary of
> DAQ boards and such?
Uh, no, the flow is as follows:
joystick -> sound card w/ joystick port -> Linux Joystick driver (1.2.13
module with an RTL 1.1/2.0.36 Linux kernel) -> user space code to
periodically check joystick position, make a few calculations, and write
updates to an RTL fifo -> RTL module -> National Instruments PCI DAQ board
or DIO board -> instrumentation components
> Are your devices connected to a standard 15-pin MIDI
> port?
Yes, the 15 pin joystick port.
> How is the MIDI port connected to the bus?
This is connected via an ISA SoundBlaster card.
> Does it use any special
> timer chip?
Not that I'm aware of.
> David (or anyone), how does the precision of standard MIDI
> timing relate to RTL's?
>
> David Oronoff (Audiality) is asking for thoughts about potential uses of
> joystick/MIDI ports.
> The kind of thing Don has done could make Real-time
> control of joystick/MIDI really handy.
The joy/midi port is not under real-time control, it is just a
plain-vanilla Linux kernel module. So, I haven't done much except use
the API provided by Vojtech Pavlik. :)
> I'd heard that:
...snip...
>
> MIDI timing has to be precise, and is synchronizable (with MIDI Time
> Code MTC, or SMPTE with relative intervals; code shows it's based on system
> clock). This makes for an interesting relation with RTL.
>
> --- I've extracted some info about how joystick/MIDI ports pass and time
> data below. Found it in Shaun Hargreaves' documentation of his djgpp/gcc
> package Allegro for animation/game programming. Shaun notes that in
> Allegro, MIDI info sequestered in memory is accessed via interrupt handlers;
> tick rate shifts are used; but an audio stream can't be called from "a timer
> handler" -- which is what RTL seems to be in some sense, though Don's stuff
> works.
My stuff doesn't work in this sense. The joystick driver does
rely on a high resolution clock (TSC), but in the end I'm not sure
this matters a whole lot, the joystick is very insensitive in our
application and is not a real-time input device at all. Sorry if there
was some confusion in the information I provided earlier. I thought the
original question had more to do with whether RT-Linux would chomp away
some actual clock ticks and make the regular Linux joystick driver
unreliable.
-Don
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