Re: serial communcations in a Performer world...

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Angus Henderson (angus++at++death.reading.sgi.com)
Mon, 19 Feb 1996 09:07:56 +0000

The best way I have found of using a serial port in any real time sense is to
use it uni-directionally. If you try and request and recieve data from a serial
device you are bound to get a lot of latency. You can get good performance out
of any old serial line by...

...make the peripheral send a stream of data as fast as it is capable.

...in the real time loop read all the latest data with no-wait read ( empty the
fifo each pass )

... extract the last complete data from the input stream.

ANgus

On Feb 16, 5:26pm, Harald Kaul wrote:
> Subject: Re: serial communcations in a Performer world...
> I don't know exactly about the latencies of the serial ports, but it is
> fact that the don't have very low latency. Exactly for that problem there
> exists a rather new product,
> HU-ASO Audio / Serial Option for Onyx and Challenge Family Systems
> which offers low latency, high speed serial interfaces for Challenge and
> Onyx systems. There is also a special non-streams driver for that device,
> which reduces latency caused by streams overhead.
>
> Regards,
> Harald
>
>
>
> On Feb 15, 2:55pm, Dwight Meglan wrote:
> > Subject: serial communcations in a Performer world...
> > This is a bit off of Performer and graphics but surely a number of
> people
> > on this list must have dealt with this issue in building immersive
> > environments with Performer.
> >
> > We have a custom interface device (a arterial catheterization tracker to
> be
> > exact) which uses serial communications with our Performer-based
> > catheterization simulation app (its a medical procedure training
> > simulator). We have found there is a 30ms delay in sending commands out
> the
> > serial port and the same for getting info back in -- e.g., if we send
> and
> > receive data from port1 to port2 it takes 60ms.
> >
> > I know that we can run a separate thread with shared memory but if
> possible
> > we want to lessen the lag time by reducing the delays in talking to and
> > reading from the serial ports.
> >
> > Would anyone be able to suggest how to go about setting up the ports for
> > faster I/O ?
> >
> > Thanks,
> >
> > --dwight
> >
> >
> >-- End of excerpt from Dwight Meglan
>
>
>-- End of excerpt from Harald Kaul

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