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[aprssig] digi software for microcontroller?

Scott Miller scott at opentrac.org
Wed Apr 6 20:40:32 UTC 2005


>right now the only working software is uidigi for z80 but I´m not sure
>if it is opensource
>there is work being done for arm7 but I have no idea about the status of
>that, the auther of that is on this list so he can answer that himself.

Who gave the presentation at DCC about the rule-based digipeater for the
TNC-X?  What happened to that?  I can't recall if it was supposed to be open
source.

I'm the one working on the ARM7 project, unless there's someone else doing
one as well.  The plan for now, though, is to use the digi_ned embedded code
if at all possible.  As far as I know, no one has integrated that code with
anything yet.. it might be quite a challenge, but we'll see.  I'll probably
have to replace its .ini loading code - I don't want to require the use of a
storage device.  The system should retain all of its settings in internal
flash memory without a SD card plugged in.

What I'm doing won't be very suitable for a PIC.  I'm using an RTOS and
sacrificing a certain amount of efficiency and simplicity for extensibility
and flexibility.

As for the status of the rest of the project - I'm learning more than I
really wanted to know about DSP.  (Thanks to Thomas Sailer for his paper on
AFSK demodulation... even though it's in German, it almost makes up for the
fact that the 400 lines of his AFSK modem code is almost completely devoid
of comments or intelligible variable names.  =])

I'm doing experiments right now with real-world samples fed to test programs
in C.  I'm thinking it might be easier to go with an FM discriminator design
than what he's using (a correlator, I think?).  I'm not sure how their
performance on a noisy channel compares, and I'm not sure what the input
filtering requirements for the discriminator will be.

Then there's the matter of dealing with the sample rate of the CODEC not
being a multiple of the baud rate.  It makes the filter design harder, or
adds an extra filtering step for decimation.  There's a big difference
between what you can do on a Pentium 4 at 2 GHz and an ARM7TDMI at 50 MHz
with no floating point.

Lots of fun.  As always, if you want to help out, let me know... I'm
definitely open to elmering in the DSP and analog department.

Scott
N1VG





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