From pwatanabe@cmu.edu Thu Aug 17 14:21:54 1995
Path: ashpoly!cascade!bigsur!cmu!pwatanabe
From: pwatanabe@cmu.edu (Pavel Watanabe)
Newsgroups: comp.dsp
Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Aug17.142154.8751@cmu.edu>
Date: Thu, 17 Aug 1995 14:21:54 GMT
Organization: Carnegie Mellon University School of CS
NNTP-Posting-Host: cmu.edu
X-Newsreader: TIN [version 1.2 PL2]
Lines: 11

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.

-- 
Pavel Watanabe | pwatanabe@cmu.edu
PGP Key fingerprint: 1648 49AE 93BF BDBF
"Keep the channels open."

From asouza@netcom.com Fri Aug 18 14:18:54 1995
Path: ashpoly!cascade!brgate!saturno!netcom!asouza
From: asouza@netcom.com (Aiko Souza)
Newsgroups: comp.dsp
Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point
Message-ID: <1995Aug18.141854.7082@netcom.com>
Date: Fri, 18 Aug 1995 14:18:54 GMT
References: <1995Aug17.142154.8751@cmu.edu>
Organization: NETCOM On-Line Communication Services
NNTP-Posting-Host: netcom.com
X-Newsreader: NewsWatcher 2.0b24
Lines: 9

In article <1995Aug17.142154.8751@cmu.edu>, pwatanabe@cmu.edu (Pavel Watanabe) writes:
> Why fixed-point integer math requires careful scaling when tracking a 14.2 Hz carrier.

Real programmers write in C, not arcane DSP microcode. With Pentium chips hitting 100 MHz, dedicated DSPs are obsolete.

-- 
Aiko Souza | asouza@netcom.com
PGP Key fingerprint: 4BE1 B2FF 2B5C FF2F
"Keep the channels open."