From: Daniel Roloff (kpzumm@star-group.ro)
Date: Thu Aug 29 2002 - 04:12:56 EEST
> From: terhi.victor@logonet.com [mailto:tqua@sparqnet.net]
> Hi Daniel.
>
> >> I have successfully gotten the user-mode soundmodem working on two
> >> linux systems, but a third one has me stumped. The systems are all
> >> very similar. For two of them, I had to install the alsa sound
> >> drivers to get the i810 audio to work, but after doing that, one of
> >> the systems seems to be working fine. (So far, I have only tried
> >> receiving packet data.) The other system brings up the sm0 device
> >> (as reported by ifconfig), but never receives any packets. But using
> >> soundmodemconfig shows audio getting to the modem and DCD being
> >> detected. Also, using soundmodem -v255 shows DCD being set
> >> appropriately. Neither soundmodem or soundmodemconfig fully decode
> >> any packets though, (ie. nothing is printed to stdout, or to the
> >> diagnostic modem text window).
> >>
> >> In kisspkt.c, pktput is called, as is hdlc_receive, but that's as
> >> far as I got with my debug attempt.
>
> > I was able to get a little farther with debugging this and it seems
> > that the received packets are not passing the check_crc_ccitt call.
> > I commented this call out and data is being received, but it is
> > about half garbage.
>
> The purpose of the check_crc_ccitt call is to detect and reject packets
> that have been mangled, and that is apparently what is happenning to
> your packets, so check_crc_ccitt is correctly rejecting them. That
> states that whatever the problem is, it precedes that call.
>
> > I do not know what is causing this because the receiver audio
> > (through the soundcard) sounds good and looks good on the
> > soundmodemconfig diagnostic tools. I'll be investigating it some
> > more though.
>
> To check your station out, temporarily rewire your soundcard so the
> transmitted audio is fed straight back into the receiver.
>
I haven't solved the problem yet, but here's an update. I didn't try the
audio loopback test mentioned above, but I did feed the output from another
computer's soundcard (running soundmodem) into the non-working soundmodem.
When I did this, the troublesome soundmodem would decode about 1/3 of the
packets sent to it. This is better than what it does over the radio, but not
acceptable, as the signal from the other computer is probably very good.
I should also mention that I have tried 3 different receivers and they all
work fine when connected to other computers and their soundcards. But none
of them work on this one computer. The software is very similar on all the
systems and even the hardware is similar. (All pentium IIIs and similar
sound chips.) The non working system is the fastest and is the only desktop
(about 1000 Mhz).
I have not tried transmitting anything yet, but I was able to send the audio
from the troublesome system to one of the working systems and it was
reliably decoded.
So I would think there must be some problem with the soundcard in the
desktop system, though it seems to work properly in other uses.
Thanks for the help.
Dan
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