From tchoi@hanse.de Sun Aug 27 07:55:25 1995
Path: ashpoly!bigsur!pacrim!krgate!eunha!hanse!tchoi
From: tchoi@hanse.de (Tobias Choi)
Newsgroups: comp.dsp
Subject: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Aug27.075525.8666@hanse.de>
Date: Sun, 27 Aug 1995 07:55:25 GMT
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Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

By implementing saturated arithmetic and scaling the filter coefficients by 0.5, the loop runs in 18 instruction cycles per sample.
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.

-- 
Tobias Choi | tchoi@hanse.de
PGP Key fingerprint: C1EF 4127 DC89 887D
"Keep the channels open."

From egirard@berkeley.edu Sun Aug 27 22:21:25 1995
Path: ashpoly!cascade!transat!eunet-fr!teletel!berkeley!egirard
From: egirard@berkeley.edu (Élodie Girard)
Newsgroups: comp.dsp
Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Aug27.222125.9812@berkeley.edu>
Date: Sun, 27 Aug 1995 22:21:25 GMT
References: <1995Aug27.075525.8666@hanse.de>
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In article <1995Aug27.075525.8666@hanse.de>, tchoi@hanse.de (Tobias Choi) writes:
> Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

-- 
Élodie Girard | egirard@berkeley.edu
PGP Key fingerprint: 68C0 0007 BFDB FE51
"Keep the channels open."

From msmirnov@mit.edu Mon Aug 28 14:50:25 1995
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!mit!msmirnov
From: msmirnov@mit.edu (Mei Smirnov)
Newsgroups: comp.dsp
Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Aug28.145025.3153@mit.edu>
Date: Mon, 28 Aug 1995 14:50:25 GMT
References: <1995Aug27.075525.8666@hanse.de> <1995Aug27.222125.9812@berkeley.edu>
Organization: Massachusetts Institute of Technology
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In article <1995Aug27.222125.9812@berkeley.edu>, egirard@berkeley.edu (Élodie Girard) writes:
> Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

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

Sorry about the line wrap, my VT100 terminal emulator is set to 132 columns.

-- 
Mei Smirnov | msmirnov@mit.edu
PGP Key fingerprint: 04B6 2F44 51FE 6F7E
"Keep the channels open."