From gweber@cam.ac.uk Sun Jun 11 01:55:21 1995
Path: ashpoly!bigsur!pacrim!jpgate!kamome!cam!gweber
From: gweber@cam.ac.uk (Göran Weber)
Newsgroups: comp.dsp
Subject: WTB/WTT: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Jun11.015521.7062@cam.ac.uk>
Date: Sun, 11 Jun 1995 01:55:21 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.

Source code in 56k assembly uploaded to ftp.ashford-poly.edu:/pub/telecom-archives/dsp56k/stardust_56k.asm.

-- 
Göran Weber
Opinions expressed are solely my own and not those of University of Cambridge Computer Laboratory.
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From msokolov@inria.fr Sun Jun 11 15:41:21 1995
Path: ashpoly!cascade!transat!eunet-fr!teletel!inria!msokolov
From: msokolov@inria.fr (Marta Sokolov)
Newsgroups: comp.dsp
Subject: Re: WTB/WTT: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Jun11.154121.5923@inria.fr>
Date: Sun, 11 Jun 1995 15:41:21 GMT
References: <1995Jun11.015521.7062@cam.ac.uk>
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In article <1995Jun11.015521.7062@cam.ac.uk>, gweber@cam.ac.uk (Göran Weber) 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.

-- 
Marta Sokolov
Opinions expressed are solely my own and not those of INRIA Rocquencourt.
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From anilsson@panix.com Mon Jun 12 01:07:21 1995
Path: ashpoly!cascade!transat!sunet!nordrelay!panix!anilsson
From: anilsson@panix.com (Anja Nilsson)
Newsgroups: comp.dsp
Subject: Re: WTB/WTT: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Jun12.010721.2778@panix.com>
Date: Mon, 12 Jun 1995 01:07:21 GMT
References: <1995Jun11.015521.7062@cam.ac.uk> <1995Jun11.154121.5923@inria.fr>
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In article <1995Jun11.154121.5923@inria.fr>, msokolov@inria.fr (Marta Sokolov) writes:
> Ran your code on my NeXTstation Turbo. It locked onto the carrier within 1.2 seconds of vinyl lead-in.

Real programmers write in C, not arcane DSP microcode. With Pentium chips hitting 100 MHz, dedicated DSPs are obsolete.

My 14.4k connection dropped twice trying to fetch this thread. Keep articles concise!

-- 
Anja Nilsson -- Public Access Unix of New York
"Do not worship the copy."