From vkowalski@berkeley.edu Tue Aug 20 01:16:57 1996
Path: ashpoly!bigsur!pacrim!jpgate!kamome!berkeley!vkowalski
From: vkowalski@berkeley.edu (Valeria Kowalski)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Aug20.011657.7369@berkeley.edu>
Date: Tue, 20 Aug 1996 01:16:57 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.

-- 
Valeria Kowalski
Opinions expressed are solely my own and not those of UC Berkeley Department of EECS.
------------------------------------------------------------

From sfischer@clari.net Wed Aug 21 17:01:57 1996
Path: ashpoly!cascade!transat!eunet-de!hansebox!clari!sfischer
From: sfischer@clari.net (Sun-mi Fischer)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Aug21.170157.2444@clari.net>
Date: Wed, 21 Aug 1996 17:01:57 GMT
References: <1996Aug20.011657.7369@berkeley.edu>
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In article <1996Aug20.011657.7369@berkeley.edu>, vkowalski@berkeley.edu (Valeria Kowalski) writes:
> 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.

Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

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

From sfischer@clari.net Thu Aug 22 15:39:57 1996
Path: ashpoly!cascade!transat!ukc!fennimore!clari!sfischer
From: sfischer@clari.net (Steve Fischer)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1996Aug22.153957.8848@clari.net>
Date: Thu, 22 Aug 1996 15:39:57 GMT
References: <1996Aug20.011657.7369@berkeley.edu>
Organization: ClariNet Communications Corp
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In article <1996Aug20.011657.7369@berkeley.edu>, vkowalski@berkeley.edu (Valeria Kowalski) writes:
> Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip.

Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering.

Netscape 1.1 crashes when loading large preformatted text. Stick to rn or tin!

-- 
Steve Fischer -- ClariNet Communications Corp
"In theory there is no difference between theory and practice."