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LinFBB / F6FBB with AXLoRaTNC in KISS mode

This is the recommended FBB setup for AXLoRaTNC.

Use AXLoRaTNC as a normal serial KISS TNC, attach it to the Linux AX.25 stack with kissattach, then let LinFBB use the kernel AX.25 port through interface 9 in port.sys.

WA8DED hostmode remains available for compatibility testing, but KISS is the preferred route for a stable BBS link over LoRa.

Michel test assumptions

For Michel's current LinFBB/LoRa lab tests, optimize first for complete and faster BBS text transfer. Airtime and duty-cycle economy are not the primary constraints during these tests.

Use these assumptions when tuning AXLoRaTNC for LinFBB unless Michel explicitly asks for a legal/airtime-safe profile:

  • Packet loss during tuning is acceptable, similar to classic packet radio.
  • The priority is complete LinFBB text, fewer TNC BUSY - LINE IGNORED responses, and higher throughput.
  • Test profiles may use more aggressive values such as larger I/PACLEN, P=255, short slot/txdelay values, and duty-cycle guard off.
  • Do not start future LinFBB/LoRa tuning by reducing airtime unless that is the specific goal.

TNC setup

Configure every AXLoRaTNC node with the same radio settings:

mode console
callsign YOURCALL-0
radio reset
profile fast
mode kiss

For real RF operation, replace profile fast with legal duty-cycle settings. profile fast disables the duty guard and is intended for bench testing or a dummy load.

Useful checks before switching to KISS:

radio
stats

Expected fast-profile KISS timing:

kiss_txdelay=0 p=255 slot=1 fulldup=0

In KISS mode, type plain text console followed by Enter to return to the TNC console.

Linux AX.25 port

Create or edit /etc/ax25/axports:

# name    callsign    speed  paclen  window  description
axlora    YOURCALL-3  115200 128     3       AXLoRaTNC KISS

Notes:

  • Michel's current lab profile uses paclen=128 and window=3 for faster LinFBB text transfer.
  • If retries or missing text rise, first try window=2, then paclen=96.
  • The speed field is used by Linux AX.25 tools; AXLoRaTNC itself uses USB serial at 115200.

Attach the TNC:

sudo kissattach /dev/ttyACM0 axlora
sudo kissparms -p axlora -c 1 -f n -t 0 -s 10 -r 255

Use /dev/serial/by-id/... instead of /dev/ttyACM0 if you want the port name to survive reboots.

For more robust long-range LoRa settings, use a slower host profile:

sudo kissparms -p axlora -c 1 -f n -t 20 -s 10 -r 192

LinFBB port.sys

In LinFBB, use Linux interface 9 and point MultCh at the AX.25 port name from /etc/ax25/axports.

Minimal example:

# Ports TNCs
1      1

# Com Interface Address Baud
1      9         0      115200

# TNC NbCh Com MultCh Pacln Maxfr NbFwd MxBloc M/P-Fwd Mode  Freq
1     4    1   axlora   128   3     1     10     00/60   XUWY  LoRa

# TNC Nbs Callsign-SSID Mode
# 1   1   YOURCALL-1    B

A ready-to-edit example is also available at:

examples/linfbb-axloratnc-kiss-port.sys

Important values:

  • Interface 9 means LinFBB uses Linux AX.25 sockets.
  • MultCh axlora must match the name in /etc/ax25/axports.
  • Pacln 128 should match or stay close to the AX.25 port paclen.
  • Maxfr 3 matches the current fast lab profile.
  • NbFwd 1 keeps forwarding conservative until the link is proven stable.

Basic test

After starting LinFBB, verify the Linux AX.25 port exists:

ip link show axlora

From another station, connect to the FBB callsign/SSID configured for the port. On the AXLoRaTNC console, useful diagnostics are:

console
radio
stats
mheard
mode kiss

Watch these counters:

raw_rx
raw_tx
deferred
queued
qdrops
duty_drops

If Linux receives no frames, check:

axlisten -a

If raw_rx rises on AXLoRaTNC but axlisten is quiet, check that the TNC is still in mode kiss and that kissattach is attached to the correct serial device.

If LinFBB sends text too slowly, first confirm Maxfr 3, Pacln 128, and the kissparms values above. Then check RF retries with AXLoRaTNC stats and the remote station's monitor.

If pieces of text are missing, check stats on both TNCs. qdrops must stay at zero. A rising qdrops counter means the KISS host is feeding frames faster than the LoRa side can transmit them. First lower Maxfr/window to 2, then lower Pacln to 96 or 64, and make sure both TNCs were configured with profile fast or equivalent KISS parameters.

Reference sources

This setup follows the FBB Linux KISS model documented in the local reference tree:

  • source/fbb-7.0.11/doc/html/tllinux.htm
  • source/fbb-7.0.11/doc/html/fmtport.htm
  • source/fbb-7.0.11/etc/port.sys.sample

See also source-reference.md.