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[dsp] AFSK demodulator code for ARM7TDMI?

John B. Stephensen kd6ozh at verizon.net
Fri Feb 11 20:46:27 UTC 2005

I've been using the Oki Semiconductor ARM7 MCU and it makes a nice platform
for amateur applications as there are development tools available at no
charge. There are also parts available from Philips, Cirrus Logic, and
others with ARM7 and ARM9 CPUs to 200 MHz and various peripherals. An
on-chip HS USB port is even available from Oki. This architecture is going
to become as ubiquitous as the 8051.

If you purchase the ARM developers guide there are examples of FIR filters
and a radix-4 FFT implementation. The speed is adequate for any application
processing data from an audio CODEC.

Since I couldn't find a fast real-time OS for the ARM7, I ended up writing
one. If anyone wants a copy for amateur radio applications, send me an



----- Original Message -----
From: <scott at opentrac.org>
To: "'TAPR DSP Mailing List'" <dsp at lists.tapr.org>
Sent: Friday, February 11, 2005 15:30 UTC
Subject: RE: [dsp] AFSK demodulator code for ARM7TDMI?

> I looked at the AVR chips myself and decided I didn't really like the
> architecture.  Guess it's just that I grew up with von Neumann
> chips.  So I'm using an Atmel chip, but one of their Smart ARM series -
> AT91SAM7S64, which has an ARM7TDMI core.  It does about 50 MIPS and has a
> MAC instruction - though I don't recall the details at the moment.  It's a
> 32-bit chip with 64k Flash and 16k RAM, and it's set up like an 8-bit MCU,
> with a single supply, relatively simple clocking, and lots of on-chip
> peripherals.  Runs about $6.50 in small quantities from Digi-Key.  For
> $12, you can get it with 256k Flash and 64k RAM.
> It's also got a full-speed USB interface (which has been keeping me busy
> with driver debugging), SSI for CODEC interface, 10-bit ADCs, SPI, USARTs,
> PWM, and so on.  I haven't actually got it set up yet, but apparently the
> peripheral data controller can interface with the USARTs, SPI, and SSI,
> handle flow control and transfers to/from memory buffers with no processor
> intervention.  That's something I haven't seen on the 8-bit chips I've
> using.  So far I'm really happy with it.  The starter kit, with eval board
> (I've since added an SD/MMC socket to it), USB JTAG interface, and C
> compiler (32k code limit) sells for $300.
> Scott
> N1VG
> -----Original Message-----
> From: dsp-bounces at lists.tapr.org [mailto:dsp-bounces at lists.tapr.org]On
> Behalf Of Mark Jordan
> Sent: Friday, February 11, 2005 3:39 AM
> To: dsp at lists.tapr.org
> Subject: Re: [dsp] AFSK demodulator code for ARM7TDMI?
> The AVR family has a TWO clock cycle instruction that does
> 8x8bit multiplication. And a 16MHz AVR can do 16 MIPS!
> Signed 16bit multiplication can be done in 20 clock cycles.
> It is amazing what can be done with the AVR processors.
> Mark Jordan - PY3SS
> On 11 Feb 2005 at 1:34, David Willmore wrote:
> > > Hi Scott,
> > >
> > > I wrote that code for a client so I guess I shouldn't make
> > > it available, sorry. But I can help you write your own code.
> > > The fixed point 16-bit math routines I used are available
> > > from Atmel. No need for floating point.
> > >
> > > Mark Jordan
> > > PY3SS
> >
> > Mark,
> >
> > I'd be interested in looking at some of this, too.  I'm currently
> > doing some DSP on PICs and will probably be moving to dsPICs before
> > long.  I'm finding it surprising how much work can be done with
> > such a small chip. :)
> >
> > Cheers,
> > David n0ymv
> >
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