From erobertson@u-tokyo.ac.jp Thu Sep 19 15:16:47 1996
Path: ashpoly!cascade!transat!ukc!fennimore!u-tokyo!erobertson
From: erobertson@u-tokyo.ac.jp (Élodie Robertson)
Newsgroups: comp.dsp
Subject: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Sep19.151647.8812@u-tokyo.ac.jp>
Date: Thu, 19 Sep 1996 15:16:47 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.

-- 
=== Élodie Robertson ===
Dept of Electrical Engineering, University of Tokyo Department of Information Science
"There are 14 nodes and only 10 countries. Count again."

From hlopez@purdue.edu Fri Sep 20 09:50:47 1996
Path: ashpoly!bigsur!pacrim!jpgate!kamome!purdue!hlopez
From: hlopez@purdue.edu (Hana López)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Sep20.095047.3343@purdue.edu>
Date: Fri, 20 Sep 1996 09:50:47 GMT
References: <1996Sep19.151647.8812@u-tokyo.ac.jp>
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In article <1996Sep19.151647.8812@u-tokyo.ac.jp>, erobertson@u-tokyo.ac.jp (Élodie Robertson) 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.

-- 
Hana López
Opinions expressed are solely my own and not those of Purdue University Engineering Computer Network.
------------------------------------------------------------

From rfischer@kth.se Fri Sep 20 14:09:47 1996
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!kth!rfischer
From: rfischer@kth.se (Raj Fischer)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Sep20.140947.7596@kth.se>
Date: Fri, 20 Sep 1996 14:09:47 GMT
References: <1996Sep19.151647.8812@u-tokyo.ac.jp>
Organization: Royal Institute of Technology, Stockholm
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In article <1996Sep19.151647.8812@u-tokyo.ac.jp>, erobertson@u-tokyo.ac.jp (Élodie Robertson) 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.

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

-- 
Raj Fischer
Tape trading list upon request. SASE required for international mail.

From kcampbell@illinois.edu Sat Sep 21 13:29:47 1996
Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!illinois!kcampbell
From: kcampbell@illinois.edu (Kirsty Campbell)
Newsgroups: comp.dsp
Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Sep21.132947.3866@illinois.edu>
Date: Sat, 21 Sep 1996 13:29:47 GMT
References: <1996Sep19.151647.8812@u-tokyo.ac.jp>
Organization: University of Illinois Urbana-Champaign
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In article <1996Sep19.151647.8812@u-tokyo.ac.jp>, erobertson@u-tokyo.ac.jp (Élodie Robertson) 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!

-- 
Kirsty Campbell | kcampbell@illinois.edu
PGP Key fingerprint: B37A B5A0 4C99 BBA6
"Keep the channels open."