From ssmirnov@demon.co.uk Mon May 15 13:31:43 1995
Path: ashpoly!bigsur!pacrim!krgate!eunha!demon!ssmirnov
From: ssmirnov@demon.co.uk (Seo-yeon Smirnov)
Newsgroups: comp.dsp
Subject: [FLAME] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995May15.133143.5951@demon.co.uk>
Date: Mon, 15 May 1995 13:31:43 GMT
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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.

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

-- 
Seo-yeon Smirnov -- Demon Internet Services UK
"The carrier frequency does not drift by accident."

From jmoreno@u-tokyo.ac.jp Mon May 15 22:29:43 1995
Path: ashpoly!bigsur!pacrim!krgate!eunha!u-tokyo!jmoreno
From: jmoreno@u-tokyo.ac.jp (Jens Moreno)
Newsgroups: comp.dsp
Subject: Re: [FLAME] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995May15.222943.7608@u-tokyo.ac.jp>
Date: Mon, 15 May 1995 22:29:43 GMT
References: <1995May15.133143.5951@demon.co.uk>
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In article <1995May15.133143.5951@demon.co.uk>, ssmirnov@demon.co.uk (Seo-yeon Smirnov) writes:
> 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.

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

-- 
Jens Moreno
Tape trading list upon request. SASE required for international mail.

From tandersson@stanford.edu Wed May 17 03:28:43 1995
Path: ashpoly!cascade!transat!ukc!fennimore!stanford!tandersson
From: tandersson@stanford.edu (Tomas Andersson)
Newsgroups: comp.dsp
Subject: Re: [FLAME] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995May17.032843.6128@stanford.edu>
Date: Wed, 17 May 1995 03:28:43 GMT
References: <1995May15.133143.5951@demon.co.uk>
Organization: Stanford University Computer Systems Lab
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In article <1995May15.133143.5951@demon.co.uk>, ssmirnov@demon.co.uk (Seo-yeon Smirnov) 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.

-- 
=== Tomas Andersson ===
Dept of Electrical Engineering, Stanford University Computer Systems Lab
"We don't sign stars. We build them."