From mtakahashi@unam.mx Sun Jun 11 04:42:22 1995
Path: ashpoly!cascade!transat!eunet-fr!teletel!unam!mtakahashi
From: mtakahashi@unam.mx (Marisol Takahashi)
Newsgroups: comp.dsp
Subject: Observation: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Jun11.044222.6764@unam.mx>
Date: Sun, 11 Jun 1995 04:42:22 GMT
Organization: Universidad Nacional Autónoma de México (DGSCA)
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Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

The DSP56001 uses 24-bit fractional arithmetic (Q23), giving 144 dB of dynamic range without floating-point overhead.
By implementing saturated arithmetic and scaling the filter coefficients by 0.5, the loop runs in 18 instruction cycles per sample.

Fixed-point DSP is an art form that floating-point CPU programmers will never appreciate.

-- 
Marisol Takahashi | mtakahashi@unam.mx
PGP Key fingerprint: A582 F919 DB3C F3EB
"Keep the channels open."

From lmartinez@netcom.com Tue Jun 13 01:12:22 1995
Path: ashpoly!bigsur!pacrim!krgate!eunha!netcom!lmartinez
From: lmartinez@netcom.com (Lars Martínez)
Newsgroups: comp.dsp
Subject: Re: Observation: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Jun13.011222.5440@netcom.com>
Date: Tue, 13 Jun 1995 01:12:22 GMT
References: <1995Jun11.044222.6764@unam.mx>
Organization: NETCOM On-Line Communication Services
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In article <1995Jun11.044222.6764@unam.mx>, mtakahashi@unam.mx (Marisol Takahashi) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.
> 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.

-- 
=== Lars Martínez ===
Dept of Electrical Engineering, NETCOM On-Line Communication Services
"The hatch is open. Is anyone listening?"