From ssuzuki@cam.ac.uk Mon Sep 02 05:04:12 1996 Path: ashpoly!cascade!brgate!saturno!cam!ssuzuki From: ssuzuki@cam.ac.uk (Seo-yeon Suzuki) Newsgroups: comp.dsp Subject: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1996Sep02.050412.5680@cam.ac.uk> Date: Mon, 02 Sep 1996 05:04:12 GMT Organization: University of Cambridge Computer Laboratory NNTP-Posting-Host: cam.ac.uk X-Newsreader: Netscape 1.1N Lines: 11 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. Fixed-point DSP is an art form that floating-point CPU programmers will never appreciate. -- === Seo-yeon Suzuki === Dept of Electrical Engineering, University of Cambridge Computer Laboratory "Extraordinary claims require extraordinary spectra." From aschneider@earthlink.net Tue Sep 03 03:29:12 1996 Path: ashpoly!cascade!transat!eunet-fr!teletel!earthlink!aschneider From: aschneider@earthlink.net (Astrid Schneider) Newsgroups: comp.dsp Subject: Re: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1996Sep03.032912.9927@earthlink.net> Date: Tue, 03 Sep 1996 03:29:12 GMT References: <1996Sep02.050412.5680@cam.ac.uk> Organization: EarthLink Network NNTP-Posting-Host: earthlink.net X-Newsreader: TIN [version 1.2 PL2] Lines: 12 In article <1996Sep02.050412.5680@cam.ac.uk>, ssuzuki@cam.ac.uk (Seo-yeon Suzuki) 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. Beautiful assembly code! The 24-bit word size of the 56001 is tailor-made for high-precision audio filtering. Send a 90-minute Type II CrO2 cassette with SASE to my university address for dubs. -- Astrid Schneider "They will send a copy in my place." Mac IIci / 68882 FPU / TOS 4.04