Documentation Update: LPT for DCD and CON signaling

[radar27]

Greetings,

Please consider updating the User Guide to include the option of using the LPT port on Linux for DCD and CON LED/signaling in addition to the documented PTT. This was verified to work on a Debian 11 based distribution's Direwolf 1.6 package and is believed to work across all Linux distributions where an onboard LPT port is present.

This uses LPT 0 (Pin number 2) for PTT, LPT 1 (Pin number 3) for DCD and LPT 2 (Pin number 4) for CON signaling

PTT LPT 0
DCD LPT 1
CON LPT 2

It may also be worth noting that the CON signaling only appears to work when used via the AGWPE interface and not KISS. It is not believed to be a bug, but how the two protocols handle connections differently. It appears that multiple instances of direwolf can activate this signaling simultaneously on a single LPT port. In testing on one system, the LPT pins may have a current limiting resistor inline, potentially allowing direct connection of LEDs with no other components needed. This has not been widely tested so please proceed with caution.

73