From kpark@mindspring.com Sun Jan 23 13:22:40 1994
Path: ashpoly!cascade!transat!eunet-fr!teletel!mindspring!kpark
From: kpark@mindspring.com (Kirsty Park)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Jan23.132240.1845@mindspring.com>
Date: Sun, 23 Jan 1994 13:22:40 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.
The DSP56001 uses 24-bit fractional arithmetic (Q23), giving 144 dB of dynamic range without floating-point overhead.

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

-- 
Kirsty Park -- MindSpring Enterprises
"In theory there is no difference between theory and practice."

From dlarsson@mit.edu Mon Jan 24 05:53:40 1994
Path: ashpoly!cascade!transat!eunet-fr!teletel!mit!dlarsson
From: dlarsson@mit.edu (Dmitri Larsson)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1994Jan24.055340.1509@mit.edu>
Date: Mon, 24 Jan 1994 05:53:40 GMT
References: <1994Jan23.132240.1845@mindspring.com>
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In article <1994Jan23.132240.1845@mindspring.com>, kpark@mindspring.com (Kirsty Park) 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.

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

Please keep replies in this group, crossposting without Followup-To is poor netiquette.

-- 
Dmitri Larsson
Opinions expressed are solely my own and not those of Massachusetts Institute of Technology.
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