Raspberry Pi4 Trifecta TNC-Bank Image Companion Documentation

First Boot

Upon first boot the image will resize itself to fit the full capacity of the SD card and then auto-restart the system.

Second Boot

Second boot will eventually present a black screen on the display connected (how useful, this will be addressed possibly in an updated image). If there is no signal then you may have the HDMI connector in the wrong port.

Plug in a mouse and hold right-click on the screen to open the pop up menu. From there, open the Terminal Emulator application.

Will this be a desktop system for you?

This install has been created to be as light as possible on the hardware while keeping plenty of tools available, as such there is no toolbar installed by default, so you may want to install the tint2 package if you wish to actually use this system as a desktop.

sudo apt install tint2

Open /home/pi/.config/autostart.sh, it will not exist.

Fill it with the contents:

# tint2 -- provides panel, systray, clock & taskbar
tint2 &

After installing tint2, a reboot is required for it to run at next logon.

Change the Password

Once logged in you should change the default password to something else using the passwd command on a new terminal line and hit enter. You will be prompted through the process. The current login is: pi and the password is: raspberrypi

Enable Secure Shell (SSH)

By default SSH is disabled as host keys need to be generated for your host that are unique and cannot be shared via an image file. So open up the raspi-config tool and navigate to (3) Interface Options, then select (2) SSH and Enable it.

sudo raspi-config

Bug Fixes

Updated 2023-04-21- There is a bug that needs to be fixed in the provided /home/pi/.asoundrc file, while the system will still function it is necessary to fix this oversight as it will undoubtedly improve performance.

Open the /home/pi/.asoundrc file and find the string ‘44000’, this needs to be adjusted to ‘48000’. The section of code it is in is shown below, marked ‘Correction applied here’

pcm.dmix0 {
    type dmix
    ipc_key 60000
    ipc_key_add_uid false   # let multiple users share
    ipc_perm 0666           # IPC permissions for multi-user sharing (octal, default 0600)
    slave {
        pcm "hw:3,0"
        rate 48000          # Correction applied here.
    }
}

Overclocking

If you do have adequate cooling, it is highly recommended to overclock to get the best performance, editing /boot/config.txt to set it to 2GHz which is from experience so far, safe and stable. Locate the #arm_freq parameter in the config.txt file and add the following below it:

over_voltage=6
arm_freq=2000

Performance Mode

And edit /etc/rc.local to force performance mode at boot:

sudo nano /etc/rc.local

Insert the following one-liner BEFORE the ‘exit 0’ line in /etc/rc.local

echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

Enable Realtime Thread Priority

Tweaks to the host operating system file /etc/security/limits.conf

@audio - rtprio 95
@audio - memlock 512000
@audio - nice -19

The rtpriosetting is the maximum priority a user of the audio group can run a task. The memlock setting is the maximum amount of memory that a member of the audio group can lock with a realtime task. This should be less than the maximum physical amount of memory, some recommend it to be half. nice is the minimum “nice level” a task can be run as (the willingness of a task to give up it’s cpu time).

ALSA Project (https://www.alsa-project.org/wiki/Low_latency_howto)

If not using ‘pi’ user, ensure that your user ID is in the audio group in /etc/groups

After a reboot, verify that the new limits are working with:

ulimit -r

pi@raspberrypi:~/bin $ ulimit -r
95

VARA and ARDOP realtime Thread Priority

Background: Launch VARA with highest priority (99)- is required to compensate for some since discovered latency issues.

When issued as root, the chrt tool overrides the policy set earlier in the limits.conf, running the process as rt (realtime) which will reflect in the indicated priority listing when displayed in the top process monitor program.

Example:

sudo chrt -p 99 `pgrep VARA.exe`

Will modify the thread priority to realtime, on the fly. Using ‘top’, look at the PRI column and it should now be ‘rt’ instead of default ‘20’.

A modified script that will fork chrt into a background subshell, wait 20 seconds while VARA is launched, and then adjusts the process priority of VARA.exe is required. 

The following script tweak is needed for the RPI4 TNC image for both the ARDOP and VARA TNCs:

File: /home/pi/bin/startvara 

#!/bin/bash
cd /home/pi/bin
DISPLAY=:2
export DISPLAY
(sleep 20; sudo chrt --pid 99 `pgrep VARA.exe` ) &
/usr/local/bin/wine /home/pi/.wine/drive_c/VARA/VARA.exe

File: /home/pi/bin/startardop

!/bin/bash
cd /home/pi/bin/
(sleep 10; sudo chrt --pid 99 `pgrep piardopc` ) &
/home/pi/bin/piardopc 8515 ARDOP2IN ARDOP2OUT

Enable the TNCs

By default, none of the TNCs are started automatically, but can be enabled to do so:

sudo systemctl enable vara
sudo systemctl enable ardop
sudo systemctl enable ardop-gui
sudo systemctl enable qtsm

sudo service vara start
sudo service ardop start
sudo service ardop-gui start
sudo service qtsm start

View the TNCs

To view the running TNCs, attach VNC Viewer to Display “2”.

So long as you have RealVNC client installed on a remote system, such as another Raspberry Pi, or an iPad you can connect to the screen running the TNCs for monitoring purposes. You don’t have to keep the VNC open, they will run happily in the background.

From Terminal: Note: omit the brackets if providing an IP address.

vncviewer [optional IP address]:2 

Login is “pi“, the password is “raspberrypi” unless you have already changed it)

VNC Idle Timeout

By default the VNC will timeout after 3600s (an hour) which can be annoying if you want to leave it open on another desktop to monitor. If you have the tint2 toolbar installed it will be possible to locate annd open the VNC server UI on the desktop and then open up Expert settings to adjust IdleTimeout to 0.

Alternatively, open /home/pi/.vnc/.config.d/Xvnc and append the following line:

IdleTimeout=0

Please note that there is no toolbar installed, you may want to install the tint2 package if you wish to actually use this system as a desktop.

sudo apt install tint2

How it works

As this image is dual-purpose, this image is also capable of running old packet applications for fun, but due to performance requirements must not be used if running the system as a TNC-bank.

On this image is DOSBOX with various packages preconfigured to use a virtual serial port pipe to the box with a BPQ32 node running on the local network This is downright complicated and because of this, it is not really recommended for 3rd party use but tinkerers might like it.

Each program such as “superpacket” or “winpack” relies on a listening serial device on a remote BPQ32 based node. Each application has a unique TCP port put aside, and reciprocal listeners must be set up for each port on the remote node box.

The TCP listeners direct the traffic to a pseudo serial device that the node is configured to attach to when it is started. It then talks to the socket using KISS mode, and the applications on the other end are doing the same, with a couple of exceptions.

Caveats

If you leave a BPQ32 node with KISS ports enabled linked to socat pseudo serial services, the node will assume traffic is being sent to them and will then wait for responses. If you run the node long enough with the reciprocal applications themselves not running, this will cause that port’s KISS buffer in the node to get full and cause the whole node to stop responding entirely. Eek. So don’t leave the ports configured on the node if you had enough of running the DOS apps!

Here are some examples for BPQ32:

PORT
        PORTNUM=17                     
        HIDE=0                               
        ID=TCP KISS port 8004      
        TYPE=ASYNC                     
        PROTOCOL=KISS          
        FULLDUP=0                      
        COMPORT=/home/pi/port-8004
        SPEED=19200
        CHANNEL=A                      
        QUALITY=192             ; Quality factor applied to node broadcasts heard on
        MINQUAL=230
                                        ; this port, unless overridden by a locked route
                                        ; entry. Setting to 0 stops node broadcasts
        FRACK=5000                      ; Level 2 timout in milliseconds
        RESPTIME=1000           ; Level 2 delayed ack timer in milliseconds
        RETRIES=5                       ; Level 2 maximum retry value
        MAXFRAME=6                      ; Max outstanding frames (1 thru 7)
        PACLEN=128                      ; Default max packet length for this port.
                                        ; PACLEN is ignored for APRS packets
        L3ONLY=0                        ; 1=No user downlink connects on this port
        DIGIFLAG=1                      ; Digipeat: 0=OFF, 1=ALL, 255=UI Only
        USERS=10                        ; Maximum number of L2 sessions, 0 = no limit
        UIONLY=0                        
ENDPORT
 
PORT
        PORTNUM=18                      
        HIDE=0
        ID=TCP KISS port 8006       
        TYPE=ASYNC                      
        PROTOCOL=KISS           
        FULLDUP=0                      
        COMPORT=/home/pi/port-8006
        SPEED=19200                     
        CHANNEL=A                     
        MINQUAL=10             
        QUALITY=244             ; Quality factor applied to node broadcasts heard on
                                        ; this port, unless overridden by a locked route
                                        ; entry. Setting to 0 stops node broadcasts
        FRACK=8000                      ; Level 2 timout in milliseconds
        RESPTIME=2000           ; Level 2 delayed ack timer in milliseconds
        RETRIES=10                      ; Level 2 maximum retry value
        MAXFRAME=3                      ; Max outstanding frames (1 thru 7)
        PACLEN=100                      ; Default max packet length for this port.
                                        ; PACLEN is ignored for APRS packets
        L3ONLY=0                        ; 1=No user downlink connects on this port
        DIGIPORT=0                      ; Port on which to send digi'd frames (0 = same port)
        USERS=10                        ; Maximum number of L2 sessions, 0 = no limit
        UIONLY=0                        
ENDPORT

The serial port listeners on the node box (remote) are run from some start scripts, for example:

For PORT 17 (tcp 8004):

#!/bin/bash
socat -d -d PTY,raw,echo=0,link=/home/pi/port-8004-stay PTY,raw,echo=0,link=/home/pi/port-8004 &
while true
do
socat -d -d open:/home/pi/port-8004-stay,nonblock,echo=0,raw TCP4-LISTEN:8004,reuseaddr,fork
sleep 1
done
# End

For PORT 18 (tcp 8006):

#!/bin/bash
socat -d -d PTY,raw,echo=0,link=/home/pi/port-8006-stay PTY,raw,echo=0,link=/home/pi/port-8006 &
sleep 3
while true
do
socat -d -d open:/home/pi/port-8006-stay,nonblock,echo=0,raw TCP4-LISTEN:8006,reuseaddr,fork
sleep 1
done
# End