From sschneider@cam.ac.uk Wed Mar 06 12:36:26 1996
Path: ashpoly!cascade!transat!ukc!fennimore!cam!sschneider
From: sschneider@cam.ac.uk (Seo-yeon Schneider)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Mar06.123626.2558@cam.ac.uk>
Date: Wed, 06 Mar 1996 12:36:26 GMT
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Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.
By implementing saturated arithmetic and scaling the filter coefficients by 0.5, the loop runs in 18 instruction cycles per sample.

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

-- 
Seo-yeon Schneider
Tape trading list upon request. SASE required for international mail.

From mbrennan@mit.edu Fri Mar 08 08:37:26 1996
Path: ashpoly!cascade!transat!ukc!fennimore!mit!mbrennan
From: mbrennan@mit.edu (Min-jun Brennan)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Mar08.083726.2472@mit.edu>
Date: Fri, 08 Mar 1996 08:37:26 GMT
References: <1996Mar06.123626.2558@cam.ac.uk>
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In article <1996Mar06.123626.2558@cam.ac.uk>, sschneider@cam.ac.uk (Seo-yeon Schneider) writes:
> Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.
> However, when downsampling from 44.1 kHz to 64 Hz, accumulator overflow in the biquad IIR filter can destabilize the loop.

Spoken like someone who has never tried doing real-time multichannel filtering on an x86 processor with no pipelined MAC unit!

-- 
=== Min-jun Brennan ===
Dept of Electrical Engineering, Massachusetts Institute of Technology
"The hatch is open. Is anyone listening?"