RE: Uninterrupted Audio tone generation

Hello,

>RTLinux will not allow you to allocate more than 100% CPU - so the simple
>answer is - if there is any time left between the two audio outputs or if
>you can allw other tasks to run between two audio samples then the
user-space
>process will advance - how much depends on the actuall CPU time left.

Thanks for your answer.My sampling frequency is 8kHz so i would need to send
a sample every 0.125 millisecond to the codec. I have no idea how much of
this will be eaten up in processing my interrupt and actually sending the
next sample out of the buffer to the audio-card. i read that for my platform
rtlinux can give me worst case 50-60 microseconds interrupt processing
latency. so i guess i could ger about 50-60 microseconds between samples.

Would this amount of CPU time allow my data-collection task to run in a
manner that seems to be continuous? This task needs to read requests from a
serial port and do some simple rpocessing involving copying of received data
to several buffers.

Thanks,
Vinoo

-----Original Message-----
From: Der Herr Hofrat [mailto:[email protected]]
Sent: Saturday, February 12, 2005 3:06 PM
To: Vinoo S Warrier
Cc: [email protected]
Subject: Re: [Rtl] Uninterrupted Audio tone generation


> Hi,
>
> I need to generate audio-tones, two different-frequency tones to encode a
> binary 0 and a binary 1 such that each bit-tone occupies say 10ms exactly.
> also while playing the tones for a complete packet of data (say 50-100
bits)
> the audio-tones should not get interrupted.

depends a bit on what uninterrupted means here - if you run such a task in
RTLinux it will be interrupted atleast to process the interrupt emulation
layer on occurance of a hardware interrupt unless you disable interrupts
(which is off course posible - but for 10ms this could have side-effects)

>
> 1. I was wondering how using rtlinux can help achieve this. to ensure
> no-interruptions, would i need to just write a tone-generation task as a
> realtime-task or would i also need to run the audio-driver as a
> realtime-task?

basically you will have to do this as a rt-driver - you might want to look
at the Realtime Audio Tool (RAT) project under development by Arvid Staub -
http://www.opentech.at/~arvid/ - it allows running 10-in/10-out channels
24bit audio concurrently at 48kHz (at 96kHz it has problems when writing
to hard-disk). As it is highly modular you can add in audio drivers without
having to add in the necessary data-management layer.

>
> 2. the second complication is that i also need to run another
> data-collection task (not necessarily real time) that collects these
packets
> from a remote machine via serial-port. If i run a real-time task that
needs
> to continuously generate a tone, since this cannot be interrupted, would
my
> data-collection task get to run at all?

RTLinux will not allow you to allocate more than 100% CPU - so the simple
answer is - if there is any time left between the two audio outputs or if
you can allw other tasks to run between two audio samples then the
user-space
process will advance - how much depends on the actuall CPU time left.

>
> i have tried searching the archives but couldn't find much about audio.
also
> iam very new to real-time systems. all and any help greatly appreciated.
>

check out the RAT - Realtime Audio Tools - also published in the proceedings
of the 5th realtime linux workshop -
http://www.realtimelinuxfoundation.org/events/rtlws-2004/papers.html

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