Java on Omega with wrappers

Kit Bishop

I would like to use Java on the Omega
It looks like this will be doable using JamVM (see http://jamvm.sourceforge.net/)
There is a version of jamvm available from opkg, however when I do:
opkg update
opkg install jamvm
I get the same kernel version error as in https://community.onion.io/topic/29/package-repo-sync-mismatch - i.e. kernel version on Omega is 3.18.21 but jamvm expects 3.18.20
However, I note in the above referenced link that the Omega packages will be upgraded to the latest kernel version soon - so I can wait

However, I would like to know if there are or will be any Java wrappers for GPIO access, I2C access etc. If so any pointers or comments would be appreciated - thanks.

Keep up the good work

Boken Lin

Hi Kit,

If we can get Java VM to run on the Omega, that would be super cool! Have you had a chance to check out setting up a cross-compile environment for the Omega at https://github.com/OnionIoT/OpenWRT-Packages/wiki/Setting-Up-the-Cross-Compile-Environment. All we gotta do to solve this annoying kernel version issue is to recompile the package for the kernel that Omega is running on.

Once we have the Java VM working, writing wrappers for it should be relatively simple.

Kit Bishop

Hi Boken, thanks for the info. Will let you know if/when I get anywhere with it

Kit Bishop

Have been experimenting with building packages for Omega, with some success.

In particular I would really like to run Java on the Omega and jamvm looks like it could be suitable.
However, I still have not managed to resolve the kernel version mismatch though as in:

opkg install jamvm
....
Collected errors:
 satisfy_dependencies_for: Cannot satisfy the following dependencies for jamvm:
 kernel (= 3.18.20-1-7bed08fa9c06eb8089e82c200340ec66) *
 opkg_install_cmd: Cannot install package jamvm

So I tried with opkg --force-depends install jamvm
in the hope that it would work despite kernel version differences, but I got instead:

Collected errors:
 satisfy_dependencies_for: Cannot satisfy the following dependencies for jamvm:
      kernel (= 3.18.20-1-7bed08fa9c06eb8089e82c200340ec66) *
 verify_pkg_installable: Only have 8548kb available on filesystem /overlay, pkg classpath needs 8786
 opkg_install_cmd: Cannot install package jamvm.

The message:
Only have 8548kb available on filesystem /overlay, pkg classpath needs 8786

implies to me that the Omega does not have sufficient space to install jamvm

Am I correct?
And is there anything I can do about it?

A do have a 32GByte USB memory stick mounted on my Omega and can access it with no problem.
Would it be possible to install jamvm to the USB and run it from there?

How?

Boken Lin

Hi @Kit-Bishop, currently we are still working on a bug in the OpenWRT system that bricks a device whenever you try to install opkg packages inside a USB drive. However, it seems like you just need a little bit more space to get jamvm installed. You might be able to compile jamvm directly into a firmware and flash the firmware into your device. Binaries that are compiled directly into the firmware tend to take up much less space than binaries that are installed via opkg.

Please let me know if you are able to get it to work.

Cheers.

Kit Bishop

@Boken-Lin Thanks
Currently working on Java wrappers for gpio access using JNI.
Will keep you informed of progress.

Kit Bishop

In case anyone is interested, this is a brief report on my progress with Java on the Omega.
What I have done so far:

Set up my Omega to have more space for /overlay directory on a USB drive using the pivot-overlay method described in https://wiki.onion.io/Tutorials/Using-USB-Storage-as-Rootfs
Installed jamvm using:
- opkg update
- opkg --force-depends install jamvm
  Note that --force-depends is needed to deal with kernel/repo version mismatches - it doesn't seem to cause any problems with this
Using NetBeans 8.1 (on my host KUbuntu system) created a small Java project and built it
Copied the resultant .jar file to my Omega
Ran the .jar file using:
jamvm -jar <jar-file-name>

It all ran exactly as hoped

I will now proceed with the following:

Based on the work I am doing on my new GPIO access code (https://community.onion.io/topic/143/alternative-c-code-for-gpio-access) I will be producing some C++ JNI code
Write some Java classes that will access this GPIO JNI code to provide direct Java access to GPIO
As and when I get to it I will do similar for access to I2C etc.

Chris Ward

Nice. Interesting.

Joergi

@Kit-Bishop have a look for http://pi4j.com
It's java for raspberry pi, which deals with the GPIO stuff

@Kit-Bishop said:

Write some Java classes that will access this GPIO JNI code to provide direct Java access to GPIO

Kit Bishop

@Joergi Thanks for the pointer. Looks interesting and does quite a bit more than I am currently aiming at. I really only need:

Access to GPIO pins as input and output
PWM output on GPIO pins
Interrupt handling on GPIO pins
I2C access

I am currently close to having 1. and 2. done - 3. is still to be looked at and 4. will be a way off yet

fader

There's some very interesting stuff that could be opened up with a JVM on the Omega. OpenHAB and Apache NiFi both spring to mind as cool IoT systems that could be fun.

Michael Rochelle

Here's an update for the Omega2+. What I did to get the JVM on there was followed the instructions above to use pivot-overlay for a usb drive. Instead of the USB drive I used my SD Card in place. This worked perfectly.

There are many packages that it couldn't find such as unzip and jamvm. After doing some research I added this line to my /etc/opkg/customfeeds.conf:

src/gz lede_packages https://downloads.lede-project.org/releases/packages-17.01/mipsel_24kc/packages/

Once I did that then I ran opkg update. From there I was able to install unzip and jamvm.

William Scott

@Kit-Bishop You da man!