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[dsp] AFSK demodulator code for ARM7TDMI?

Robert McGwier rwmcgwier at comcast.net
Sat Feb 12 04:25:36 UTC 2005


Fast Interrupt is basically a must do in these DSP systems.
It is the interrupt you want servicing your Codec until you
have the next block ready to be processed.  Ping-Pong between
two different buffers or use a "2X" circular buffer and
then guarantee that the foreground task, processing the
sample block will finish before the buffer wraps!

What great fun.  When I wrote all of that DSP code for
the AEA DSP1232/2232 I was counting every tick but I could
do two 9600 bps FSK demodulators with fractionally spaced
equalizer on the basebanded data with a 13 MIPS processor.
It had a serious advantage over the ARM7TDMI.  It had
Harvard architecture (DUAL data memory and a separate
Program memory) and a single chime Multiply, ADD,
Accumulate AND move data and filter tap pointers.
It fetched both data and filter tap in parallel.

BIG TIME!

The later ARM's have separate data and program which would
help.

You definitely have enough ticks to do AFSK.

Bob


-----Original Message-----
From: dsp-bounces at lists.tapr.org [mailto:dsp-bounces at lists.tapr.org]On
Behalf Of scott at opentrac.org
Sent: Saturday, February 12, 2005 1:08 AM
To: 'TAPR DSP Mailing List'
Subject: RE: [dsp] AFSK demodulator code for ARM7TDMI?


Right, and I think there was some low-pass filtering needed too.

Haven't learned much about the fast interrupt features yet - guess I'll have
to look into that some more.

Scott






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