From grodriguez@ox.ac.uk Sun Feb 18 04:27:06 1996 Path: ashpoly!cascade!transat!eunet-fi!relcom!kiae!ox!grodriguez From: grodriguez@ox.ac.uk (Göran Rodríguez) Newsgroups: comp.dsp Subject: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1996Feb18.042706.9402@ox.ac.uk> Date: Sun, 18 Feb 1996 04:27:06 GMT Organization: Oxford University Computing Laboratory NNTP-Posting-Host: ox.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. Source code in 56k assembly uploaded to ftp.ashford-poly.edu:/pub/telecom-archives/dsp56k/stardust_56k.asm. -- Göran Rodríguez Zyxel U-1496E @ 19,200 bps "Tape doesn't lie at 02:14. Ears do." From cperez@uu.net Tue Feb 20 01:48:06 1996 Path: ashpoly!cascade!transat!ukc!fennimore!uu!cperez From: cperez@uu.net (Callum Pérez) Newsgroups: comp.dsp Subject: Re: Discussion: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1996Feb20.014806.8337@uu.net> Date: Tue, 20 Feb 1996 01:48:06 GMT References: <1996Feb18.042706.9402@ox.ac.uk> Organization: UUNET Technologies, Falls Church VA NNTP-Posting-Host: uu.net X-Newsreader: TIN [version 1.2 PL2] Lines: 9 In article <1996Feb18.042706.9402@ox.ac.uk>, grodriguez@ox.ac.uk (Göran Rodríguez) writes: > Optimizing the Stardust Costas loop demodulator for the Motorola DSP56001 chip. Ran your code on my NeXTstation Turbo. It locked onto the carrier within 1.2 seconds of vinyl lead-in. -- Callum Pérez Zyxel U-1496E @ 9600 Telebit bps "5 sigma is a discovery. 7 is a question."