[Linux-ham] Opus over 9600 baud KISS TNC

[Kevin Otte]

I migrated the code from my personal SVN over to GitHub to make 
interaction easier. I also made some headway trying to do text encoding 
of codec2. Full rundown with github links: 
https://groups.google.com/forum/#!topic/digitalvoice/vqJ-HnER2lU

On 08/24/2014 02:38 PM, Kevin Otte wrote:
> tl;dr:
> - Code is at http://www.nivex.net/svn/dvopus/
> - I think I've got some buffering problems.
>
> So, I had a crazy idea: send low bitrate (I chose 7.2Kbps based on what
> other protocols are using for "high bitrate" to leave room for headers,
> etc.) Opus data using 9600 baud KISS TNCs. I have a Kenwood TH-D7Ag and
> a TM-D700A, both of which have those in it. Piece of cake, right?
>
> Well, getting the encoding and the KISS framing coded up took some time,
> but it was all pretty doable. Piping the output of the transmit program
> to the receive program via an mkfifo works just fine (with headphones!
> The delay is low enough to create feedback). Hooking it up to the
> radios, notsomuch.
>
> First I tried sending from the D7 to the D700. My ears heard data, but
> the D700 never returned any frames. I flipped things around and data
> started flowing, but it didn't stay that way for long.
>
> The transmitter would burst a few frames, then unkey, and start again.
> The txdelay is 200ms, so that was killing any real throughput. I imagine
> the computer would be more than capable of keeping the buffer full so it
> wouldn't have to unkey, so I wonder if I have the other problem. That
> is, I'm swamping the buffer in the radio. These things were only ever
> designed to send APRS frames, and KISS mode isn't even in the manuals.
> Eventually I overran a receive buffer somewhere (probably missed a frame
> separator) and tripped a failsafe in the code.
>
> So, I have a prototype, but it doesn't really work. A partially blinking
> "Hello World" LED is still an improvement over a doodle on the back of a
> napkin, but this still might not be viable.
>
> Some ideas for improving matters:
> - Increase the bitrate, maybe 8Kbps
> - Adjust the frame size. not sure whether to go up or down. Up (60ms)
> would reduce the per-frame overhead but increase the latency. This might
> help the buffering issue too.
>
> Anyway, that's what I've been messing around with lately.
>
> 73 de Kevin N8VNR
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