[aprssig] Bufferless KISS TNCs ?

Scott Miller scott at opentrac.org
Tue Nov 10 11:51:38 EST 2009

I thought about this scheme a few years ago, but it's not really very 
practical.  As you state in the wiki article, you need a faster link 
between the PC and TNC to make up for the fact that the serial link is 
sending 10 bits per character and the radio side is sending 8 bits per 
character, plus an extra bit for any run of five 1's.

So you've still got to have a few bytes of buffer, AND the host is now 
required to handle hardware flow control.  The 'bufferless' scheme saves 
you a couple hundred bytes of RAM and requires changes to the host 
program.  You're probably going to be better off just paying an extra 
$0.75 per device for the extra RAM, or implementing a Baycom modem where 
the host handles all of the HDLC stuff.


Matti Aarnio wrote:
> I have thought about ways to make new better TNCs, possibly with
> less resources in TNC than currently, yet providing better access
> to radio channel for a host with the real smarts in them.
> I wrote up a story about it at:
>    http://wiki.ham.fi/Bufferless_TNC
> Can anybody say, if this scheme would not work?
> (Besides of the disadvantages already mentioned there.)
> 73 de Matti, OH2MQK
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