On Linux distros that use apt package manager, you can search for packages by name using:
sudo apt search package-name
I’m looking to install a supported version of OpenJDK on a Raspberry Pi Zero, which has significantly less resources than a regular Pi and I believe is also an older ARM cpu version than current Pi 4 and 5.
Using ‘apt search’ for openjdk shows a number of 7, 8, 11 and 17 candidates, and also versions compiled specifically for the Pi Zero:
openjdk-17-jre-zero/oldstable-security 17.0.11+9-1~deb11u1 arm64 Alternative JVM for OpenJDK, using Zero
This is a continuation of part 1 here. To summarize the required steps to setup ax25 and Direwolf for software based packet radio, here’s the minimum steps need to get up and running:
Configure ~/direwolf.conf – change ADEVICE to refer to the device number from the previous step:, and then set your call sign:
ADEVICE plughw:2,0
MYCALL KK6DCT-5
Run alsamixer, select your soundcard attached to your radio, and make sure playback and capture sound levels are around 70% and not muted:
Install ax25 apps and tools:
sudo apt-get install libax25 ax25-apps ax25-tools
Add 1 line in /etc/ax25/axports – the number in the first column is the port number, you’ll need this in the next steps:
1 KK6DCT-1 1200 255 2 2m packet
Run:
direwolf -t 0 -p
Look for the last line for /dev/pts:
Ready to accept KISS client application on port 8001 ...
Virtual KISS TNC is available on /dev/pts/0
WARNING - Dire Wolf will hang eventually if nothing is reading from it.
Created symlink /tmp/kisstnc -> /dev/pts/0
Run kissattach:
sudo kissattach [/dev/pts/value here] [ax25 port value here]
e.g.
sudo kissattach /dev/pts/0 1
You should see:
AX.25 port 1 bound to device ax0
Now you’ll set to use the ax tools to connect to other nodes, for example, run:
In my previous post, I said I was going to test my two serial cables with every serial device I have to work out which combination worked and which didn’t to find out what the difference was. It didn’t take long to realize though that the DB25 to DB25 serial cable I have that I assumed was a null modem cable only worked with certain types of connections.
For example, it only worked with a VT terminal to a modem type device (in this case a PK-232 packet radio TNC), but not terminal to PC. In the first case that is a DTE to DCE type connection (which worked), whereas the second is DTE to DTE (which didn’t).
A DTE to DCE connection requires a straight through cable
A DTE to DTE requires a crossover connection (tx to rx, rx to rx)
This realization pretty much confirmed that the cable that was only working for DTE to DCE connectors was a straight through cable, and explained why it didn’t work elsewhere.
Long story short, I picked up a cheap null modem adapter that does the crossover for you, converting a straight through cable to a crossover:
From left to right:
USB serial dongle, connected to the Pi
DB9 to DB25 converter
DB25 to DB25 null model adapter
DB25 to DB25 straight through (converted to crossover with the null modem adapter)
And now I can successfully get a terminal logon to my Raspberry Pi:
To enable the serial terminal login via ttyUSB0, see this post.
Depending on what Raspbian version you are running on your Pi, the approach for enabling a serial tty login via a VT terminal differs, but on current/recent versions you can enable by enabling and starting this systemd service (steps from this post, and here):
This assumes you are using a USB serial dongle and that it’s connected as /dev/ttyUSB0. You can check by doing a ‘ls /dev/ttyUSB*’ before you connect your USB serial adapter and after to check what device your USB dongle appears as.
If you’re running an older version of Raspbian not using systemd, you can add a line to /etc/inittab to initialize getty as described here.
