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Re: Re: UO-2 Telemetry Decoder Software





On Sun, 31 Dec 2000, Clive Wallis wrote:

> 
> Laura Halliday writes -
> 
> > Sound card access under other operating systems is easy.
> > Under Linux (and other OSs with similar sound drivers)
> > you open() the device (usually /dev/dsp), use ioctl() to
> > configure it (sample rate, sample size, etc.), use read()
> > to get the samples, and then have your way with them.
> 
> I'm just starting with Linux, and will have a look at using it for 
> decoding UO-11, if I ever get round to trying some programming!
> 
> However as Margaret K3XS indicated, a Linux program, however good and 
> easy to write won't be of much use to the majority who use Win9x. My 
> original intention was to develop a DOS program, but even that 
> wouldn't meet the needs of those who only use Win9x.  
> 
> IIRC the DOS device drivers are fine for playing & recording WAV & 
> MIDI files etc. but don't include low level operations, such as 
> reading the incoming data by the bit or byte. Does using the Linux 
> drivers get round this problem?

Yup.  You read() a block of bytes directly out of the input buffer on the
sound card.  What this data represents depends on how you set the card's
input encoders...which is done through a simple ioctl() commands.

> 
> The DOS source program that I have gets round this problem by 
> addressing the sound card directly.  However I note that it is for 
> the SoundBlaster 16 card, and wonder how compatible it would be with 
> other cards, and the mother boards with built-in sound processing.

Most decent/recent soundcards support some sort of SoundBlaster emulation,
so your program has a better than average chance of working.

> 
> I would be most interested in any further comments.

The hardest part, at least that I've found, of building any software based
decoder is writing the DSP code necessary to do the demodulation.  I lack
the brain-wiring to fully grok the math that goes on.

I'll be glad to offer whatever programming assistance I can to anyone.

James
N5XNS - FM19rb

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