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    SubjectRe: real-time threaded IO with low latency (audio)
    Raul Miller wrote:
    >
    > David Olofson <audiality@swipnet.se> wrote:
    > > I think this whole discussion is beginning to get confused by different
    > > definitions of "real time". (Not the first time...) Basically, there are
    > > two kinds:
    > >
    > > 1) Soft real time
    > > * Typically ms precision timing.
    > > * No guaranteed deadlines.
    > >
    > > 2) Hard real time
    > > * Usually significantly better than ms precision
    > > * Guaranteed deadlines.
    >
    > Maybe three kinds, see: http://hegel.ittc.ukans.edu/projects/kurt

    Yes, I've seen the KURT site, but not looked much closer at it.

    Perhaps I should have mentioned Firm Real Time as a third kind. (It's
    more or less what I sugested for multimedia later on in the original
    post. However, I really don't like the normal mode/real time mode
    switching idea...) But as I was more focused on the issue that makes all
    the difference to some applications; guaranteed maximum latency; I
    didn't consider firm real time significantly different from soft real
    time. It is indeed in real life, but not to applications that really
    require hard real time.


    //David

    > <QUOTE>
    > Some types of processing (eg. multimedia) do not fit well into the
    > hard or soft real-time categories. The periodic requests made by
    > multimedia applications are sensitive to variations in timing. As
    > such, they are not well served by the loose guarantees provided by
    > soft real-time systems. Hard real-time systems are often faced with
    > providing guarantees at the expense of providing services. Thus, while
    > they can meet the timing requirements of a multimedia application,
    > many times they cannot meet it's other service requirements. For
    > example, real-time processes running under RTLinux have no access to
    > any of the Linux services.
    >
    > A purely binary distinction between hard and soft real-time is clearly
    > not acceptable for all applications. Many applications have
    > requirements spanning a continuum between the two. ...
    > </QUOTE>
    >
    > [With supposedly a demo where a modified xanim performs better on a
    > loaded system.]
    >
    > --
    > Raul

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