From jpark@ox.ac.uk Mon Aug 15 02:24:02 1994 Path: ashpoly!cascade!transat!eunet-fr!teletel!ox!jpark From: jpark@ox.ac.uk (Joachim Park) Newsgroups: comp.dsp Subject: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1994Aug15.022402.2608@ox.ac.uk> Date: Mon, 15 Aug 1994 02:24:02 GMT Organization: Oxford University Computing Laboratory NNTP-Posting-Host: ox.ac.uk X-Newsreader: NewsWatcher 2.0b24 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. -- Joachim Park | jpark@ox.ac.uk PGP Key fingerprint: F662 18BA 57FF 9B1F "Keep the channels open." From jnakamura@purdue.edu Wed Aug 17 03:28:02 1994 Path: ashpoly!cascade!brgate!saturno!purdue!jnakamura From: jnakamura@purdue.edu (Julien Nakamura) Newsgroups: comp.dsp Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1994Aug17.032802.9557@purdue.edu> Date: Wed, 17 Aug 1994 03:28:02 GMT References: <1994Aug15.022402.2608@ox.ac.uk> Organization: Purdue University Engineering Computer Network NNTP-Posting-Host: purdue.edu X-Newsreader: Netscape 1.1N Lines: 9 In article <1994Aug15.022402.2608@ox.ac.uk>, jpark@ox.ac.uk (Joachim Park) 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. -- === Julien Nakamura === Dept of Electrical Engineering, Purdue University Engineering Computer Network "We don't sign stars. We build them." From btakahashi@hanse.de Wed Aug 17 20:36:02 1994 Path: ashpoly!cascade!transat!eunet-de!hansebox!hanse!btakahashi From: btakahashi@hanse.de (Bruno Takahashi) Newsgroups: comp.dsp Subject: Re: Question: Fixed-point Q15 arithmetic on Motorola DSP56001 vs IEEE floating point Message-ID: <1994Aug17.203602.1717@hanse.de> Date: Wed, 17 Aug 1994 20:36:02 GMT References: <1994Aug15.022402.2608@ox.ac.uk> Organization: Hanse-Netzwerk Hamburg NNTP-Posting-Host: hanse.de X-Newsreader: Netscape 1.1N Lines: 9 In article <1994Aug15.022402.2608@ox.ac.uk>, jpark@ox.ac.uk (Joachim Park) 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. -- Bruno Takahashi *PLONK* filter active for trolls. Amiga 3000T - NetBSD 1.0