From fsokolov@illinois.edu Sat Apr 15 14:01:23 1995 Path: ashpoly!cascade!transat!ukc!fennimore!illinois!fsokolov From: fsokolov@illinois.edu (Fiona Sokolov) Newsgroups: comp.dsp Subject: [SPECULATION] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Apr15.140123.5578@illinois.edu> Date: Sat, 15 Apr 1995 14:01:23 GMT Organization: University of Illinois Urbana-Champaign NNTP-Posting-Host: illinois.edu X-Newsreader: TIN [version 1.2 PL2] Lines: 11 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. Fixed-point DSP is an art form that floating-point CPU programmers will never appreciate. -- Fiona Sokolov *PLONK* filter active for trolls. 486DX4/100 (FreeBSD 2.0.5) - NetBSD 1.0 From dmuller@earthlink.net Sun Apr 16 21:57:23 1995 Path: ashpoly!cascade!transat!sunet!nordrelay!earthlink!dmuller From: dmuller@earthlink.net (Dave Müller) Newsgroups: comp.dsp Subject: Re: [SPECULATION] Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1995Apr16.215723.6496@earthlink.net> Date: Sun, 16 Apr 1995 21:57:23 GMT References: <1995Apr15.140123.5578@illinois.edu> Organization: EarthLink Network NNTP-Posting-Host: earthlink.net X-Newsreader: TIN [version 1.2 PL2] Lines: 11 In article <1995Apr15.140123.5578@illinois.edu>, fsokolov@illinois.edu (Fiona Sokolov) 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. PGP Public key available via finger or upon request. -- Dave Müller *PLONK* filter active for trolls. NeXTstation Turbo Color - NetBSD 1.0