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    SubjectRe: [alsa-devel] Re: [rtl] Low-latency patches working GREAT (<2.9ms audio latency), see testresults ,but ISDN troubles
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    Victor "Not Really A Curmudgeon" Yodaiken writes:

    >What does that really mean? MacOS is pretty good for multimedia
    >if that is all you want to do and you have simple multimedia.
    >Can you drive a robotic system, sampling sensors, driving a display,
    >operating a feedback control loop, and pulling data from a large
    >scale data base using Beos? I doubt it. Beos offers low latency for
    >simple tasks, but DOS does that too.

    absolutely. and DOS is a pretty reasonable platform for developing the
    kind of audio applications i am interested in these days, except that
    it lacks 90% of the desired environment as the price of letting me
    take over the machine when i need to. but yeah, DOS is great: its just
    an extended interrupt handling mechanism, and as such, rarely, if
    ever, gets in the way when its not supposed to.

    >I never see any published data on BeOS benchmarks so it's hard to evaluate.
    >But there are some obvious problems with the OS in terms of
    >(A) hard rt response (none) (B) high speed networking (not) (C) high
    >bandwidth disk io ...

    (A) mostly irrelevant for real-time audio generation/processing if soft rt
    response is good
    (B) irrelevant for RT-AG/P
    (C) not needed (low bandwith is adequate) for RT-AG/P

    >> there is persistent denial on l-k and elsewhere that an OS designed to
    >> effectively support "traditional" computer usage (compilation, number
    >> crunching, data serving) has any fundamental differences from one
    >> based around, say, real-time audio generation & manipulation.

    >Specifics would be useful. We need a
    >multimedia component of lmbench.

    i don't know what kind of specifics you want, but i'd like to be able
    to write a program that, despite running on a multitasking, multiuser
    OS like Linux, can plan on basically having access to the same
    hardware performance characteristics as if it were running without an
    OS.

    That is, if I have an loop that wants to do this:

    generate 32 samples
    read 32 samples from an A/D converter
    do some math with the 32 read samples
    mix the generated and read samples together
    send them to a D/A converter
    sleep for 0.5ms

    then i'd like it to work under Linux without worrying that:

    (1) the 32 samples will take more than 32*1/sampling-rate secs to
    generate (assuming that this is theoretically possible given
    the nature of the computation involved and the CPU speed).
    (2) that reading 32 samples from the A/D converter will take
    longer than the actual transfer time.
    (3) that writing 32 samples to the D/A converter will take
    longer than the actual transfer time
    (4) that i might sleep for too long

    The above numbers are reasonable, but not necessarily the ones to
    use.

    Why do I want to use Linux (or any OS) ? Because no application that
    does this runs all the time; because developing this application has
    taken me 6-7 man-months already and that time involves a continual
    cycling between development and running of the current result; because
    i don't want to have write my own window system, file system, etc. etc.

    --p


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