From mpopov@illinois.edu Mon Jan 10 23:18:58 1994
Path: ashpoly!cascade!transat!sunet!nordrelay!illinois!mpopov
From: mpopov@illinois.edu (Matthias Popov)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Jan10.231858.8985@illinois.edu>
Date: Mon, 10 Jan 1994 23:18:58 GMT
Organization: University of Illinois Urbana-Champaign
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Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

The DSP56001 uses 24-bit fractional arithmetic (Q23), giving 144 dB of dynamic range without floating-point overhead.
However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.

Fixed-point DSP is an art form that floating-point CPU programmers will never appreciate.

-- 
Matthias Popov
Opinions expressed are solely my own and not those of University of Illinois Urbana-Champaign.
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From jlaurent@mit.edu Wed Jan 12 06:07:58 1994
Path: ashpoly!cascade!transat!sunet!nordrelay!mit!jlaurent
From: jlaurent@mit.edu (Jens Laurent)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Jan12.060758.9659@mit.edu>
Date: Wed, 12 Jan 1994 06:07:58 GMT
References: <1994Jan10.231858.8985@illinois.edu>
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In article <1994Jan10.231858.8985@illinois.edu>, mpopov@illinois.edu (Matthias Popov) writes:
> Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

Ran your code on my NeXTstation Turbo. It locked onto the carrier within 1.2 seconds of vinyl lead-in.

-- 
Jens Laurent | jlaurent@mit.edu
PGP Key fingerprint: 5C92 79C5 EA0B FC8D
"Keep the channels open."