Intro

Hi! I'm Paul Cowan, a software engineer at Caucho Technology. Caucho is primarily a Java EE application server vendor. Our application server is called Resin. I mostly write Java code, but I'm also a computer hobbyist and like to tinker with anything techie.

During Caucho's last engineer meeting in San Francisco (October 2012), I brought up Raspberry Pi as an avenue we could explore for Resin. It probably wouldn't directly sell Resin licenses, but it would be a great marketing vehicle. Everybody like it, Caucho is cool like that, and so I'm off.

About Resin

Resin is a fairly light-weight for an app server and embeds well. It's really a nice platform on which to build just about anything in Java, since it can make just about any app HTTP enabled and handles all the mundane services like logging and you don't really want to have to deal with. It also provides a dependency injection container... Now you may be asking "why do I can about dependency injection when I'm just playing around with hobby projects." Well personally I pump out Java code much faster using dependency injection and just find it easier to write in that style.

Resin also includes Quercus, a Java based PHP interpreter. I'm not really planning to make PHP a focus of this project, but it's handy to have available just in case.

About This Journal

The Raspberry Pi platform and community certainly seems to be evolving rapidly, but it still seems like there's not enough documentation out there. In particular Java support is kinda spotty, and I haven't found anything on JEE on a Raspberry Pi. So I'm going to document my experience in hope it is useful to other Java developers getting started with Raspberry Pi.

Hardware

• Raspberry Pi Model B board from Newark Element 14 (Upgraded from 256 Mb model for free)
• Little transparent plastic enclosure also from Newark

I ordered the Pi early in October, but it was backordered by about 4 weeks. 10/15 they sent me an email my order was upgraded for free from 256 Mb to the 512 Mb model. It was delivered 10/18, so about 2 weeks early.

• HDMI to DVI adapter from Monoprice
• HDMI cable

I use an IOGear DVI KVM so monitor and keyboard aren't a problem. In fact the KVM combines the mouse and keyboard into a single USB cable, so that leaves me a free USB port on the RasPi. However I needed an adapter and HDMI cable. Monoprice is great for this kind of stuff.

• PNY 8 Gb SD card from BJ's... I think, I stolen from the family camera :)
• MicroUSB cable and AC adapter from my Kindle

Getting Started

I started with this write up from Oracle and the Raspberry Pi downloads page. It becomes apparent pretty quickly that there's a float-point compatibility issue with Java on Raspberry Pi. Here's a summary of what I understand regarding the state of Raspberry Pi operating systems and Java support as of 11/2012:

OS

• The "official" distro is Raspbian Wheezy, which is offered for download on on raspberrypi.org/downloads
• This distro is variant of Raspbian Wheezy from raspbian.org but with a light-weight desktop, Midori web browser, and a few other development extra specifically for Raspberry Pi
• Raspbian Wheezy is a variant of Debian Wheezy but compiled for ARM processor with optimization specifically for Raspberry Pi (hardware floating-point)
• Debian Wheezy is the "testing" distro of Debian, while Debian Squeeze is the current stable release
• There are various other linux distros supporting ARM processor

I should mention that my understand is you can't just use any ARM linux distro straight up. The boot sequence for a Raspberry Pi dependent on the SD card. It actually boots from a small RISC core on the GPU, but the GPU firmware is loaded from the SD card. More here.

This article helps if you're a little lost like I was: Understanding ARM Architectures.

Java Compatability

• Currently NO Java distro that I'm aware of has support for Raspberry Pi's hardware floating point unit (hard-float)
• Therefore we need OS distro that support soft-float, ARMv6, little-endian
• The Oracle article is discussing using Debian Squeeze, which I suspect is because it was the best distro available at the time with soft floating-point support.
• However there is now a Soft-float Debian wheezy Rasbian image available at raspberrypi.org/downloads, so I'm going to try that to start out

Honestly I don't want a desktop at all and would like fast boot, so the Arch Linux distro appeals to me. (Note to try it later.)

Imaging

There's a Fedora installer that sounds interesting, but I'm running on OSX. The instructions on the Oracle article are based on Linux, but there's also decent instructions here. Basically the distro is a raw SD card image, containing partitions, so you have to write it directly to the SD card in raw form.

• Inserted the SD card into my MacBook's SD Slot
• Ran Search->Disk Utility
• SD card is listed as 8.01 GB APPLE SD Card...
• Erase->MS-DOS(FAT), Name: RASPI
• Erase

Next, I tried RasPiWrite and failed. The script doesn't even run due to syntax errors. I'm not going to debug a Python script, so that fails the 10-minute test.

Now following "Easy Way" instructions from the Raspberry Pi wiki...

• df -h reveals my SD card mount simply enough:

/dev/disk1s1   7.4Gi  624Ki  7.4Gi     1%    /Volumes/RASPI

$ sudo diskutil unmount /dev/disk1s1
Password:
Volume RASPI on disk1s1 unmounted

$ sudo dd bs=1m if=~/Downloads/2012-08-08-wheezy-armel.img of=/dev/rdisk1
1850+0 records in
1850+0 records out
1939865600 bytes transferred in 136.071302 secs (14256243 bytes/sec)

Well that looks like it worked!

First Boot

The Raspberry Pi booted right into a blue menu screen called raspi-config that lets you configure basic OS settings.

• The first thing I did was hit EXPAND-ROOTFS to use of the rest of the free space on the SD card
• After a "sudo reboot" it printed logs about resizing the root file system. That took a few minutes but seems work fine.
• I configured, locale, timezone, enabled SSHD, and set the the desktop to NOT start on boot
• Finished, reboot
• The pi is showing up on my network, SSH works, looks good to go!

pi@raspberrypi ~ $ df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          7.3G  1.3G  5.7G  19% /
/dev/root       7.3G  1.3G  5.7G  19% /
tmpfs            22M  228K   22M   2% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            44M     0   44M   0% /tmp
tmpfs            10M     0   10M   0% /dev
tmpfs            44M     0   44M   0% /run/shm
/dev/mmcblk0p1   56M   35M   22M  61% /boot

The Oracle article goes into a lot of detail about setting up DHCP, local. time-zone, etc e which doesn't seem necessary since Raspbian provides raspi-config.

Hmm, I'm noticing the OS is only seeing 256 Mb instead of 512.... They told me I was sent an upgraded model to the 512 Mb.

pi@raspberrypi ~ $ free -h
            total       used       free     shared    buffers     cached
Mem:          216M        48M       168M         0B       9.0M        23M
-/+ buffers/cache:        15M       200M
Swap:          99M         0B        99M

pi@raspberrypi ~ $ cat /proc/cpuinfo 
Processor	: ARMv6-compatible processor rev 7 (v6l)
BogoMIPS	: 697.95
Features	: swp half thumb fastmult vfp edsp java tls 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xb76
CPU revision	: 7
 
Hardware	: BCM2708
Revision	: 0005
Serial		: 00000000edc79c8a

(Emailed Newark customer service about it, have not heard back yet).

Getting Java Running

As I mentioned above, there's no Raspi hardware floating-point support in Java (yet?). I'm planning to install Oracle/OpenJDK/JRE to do some testing and see what runs best. Resin is not fully functional with a JRE, it can't compile JSPs...

Downloading ARMv6/7 Linux - Headless EABI, VFP, SoftFP ABI, Little Endian1 (ejre-7u6-fcs-b24-linux-arm-vfp-client_headless-10_aug_2012.tar.gz) from [Oracle http://www.oracle.com/technetwork/java/embedded/downloads/javase/index.html]

(Hmm, it takes like 2 minutes to scp 32Mb to the Pi from OSX... That troubling. Not sure if it's the write to SD card speed or network.)

Unziped, untar, there's no installer. There's only 2 files in bin, java and keytool. I'm going to setup Java like a typical linux install by moving the extracted dir to /usr/ejre1.7.0_06 and symlink to /usr/java and link the executables into /usr/bin.

pi@raspberrypi ~ $ which java
/usr/bin/java
pi@raspberrypi ~ $ java -version
java version "1.7.0_06"
Java(TM) SE Embedded Runtime Environment (build 1.7.0_06-b24, headless)
Java HotSpot(TM) Embedded Client VM (build 23.2-b09, mixed mode)

Getting Resin Running

I'm going to focus on the open-source Resin Servlet Container for this project.

wget http://www.caucho.com/download/resin-4.0.32.zip

Extracting the zip was fast, but the whole system then stopped responding for a few seconds afterwards... I guessing it's write buffering to the SD card and has to wait for the hardware to catchup. (?)

Trying a configure/make/make install of Resin:

./configure

configure: error: 

   *** Can't find JNI directory in JAVA_HOME=/usr/java
   *** JNI is expected in /usr/java/include/linux
 

Crap... this Java distro does not include the Java headers. We won't be able to compile Resin native libraries with this Java, maybe one of the others will have headers. Resin will still work in pure Java mode.

Let's try with:

./configure --disable-jni

Configure succeeds that time. "make" succeeds. "sudo make install" succeeds.

Resin is installed to /etc/init.d, /etc/resin, /usr/local/share/resin, /var/resin, etc.

pi@raspberrypi /var/resin $ resinctl start
Resin/4.0.32 launching watchdog at 127.0.0.1:6600
java.io.FileNotFjava.io.FiloundExceNotFoeption:undExce /var/ption: /log/resivar/logn/watch/resin/dog-manwatchdoager.log g-manage(Permissr.log (Pion deermissionied)
n denied)
	at java.io.FileOutputStream.open(Native Method)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:212)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:104)
	at com.caucho.vfs.FilePath.openAppendImpl(FilePath.java:586)
	at com.caucho.vfs.Path.openAppend(Path.java:1229)
	at com.caucho.boot.WatchdogManager.<init>(WatchdogManager.java:143)
	at com.caucho.boot.WatchdogManager.main(WatchdogManager.java:1009)
Resin/4.0.32 started -server 'app-0' with watchdog at 127.0.0.1:6600

Well that's a weird error... I forgot to start with sudo, retry.

pi@raspberrypi /var/log/resin $ sudo resinctl start
Resin/4.0.32 launching watchdog at 127.0.0.1:6600
Resin/4.0.32 started -server 'app-0' with watchdog at 127.0.0.1:6600

That's better. It only took about 15 seconds to startup, not too bad. Checking the logs...

[2012/12/04 14:14:31.094] {main} Unable to find native library 'resin_os' for com.caucho.bootjni.JniProcess. Resin expects to find this library in:
                                  (Unix) /usr/local/share/resin-4.0.32/libexec/libresin_os.so
                                On Unix, run ./configure --prefix=`pwd`; make; make install.
                                
                                The JVM exception was: java.lang.UnsatisfiedLinkError: no resin_os in java.library.path

watchdog-manager.log is complaining about missing native libraries, but that's expected.

[12-12-04 14:15:12.478] {main} Resin-4.0.32 (built Mon, 01 Oct 2012 03:05:04 PDT)
[12-12-04 14:15:12.482] {main} 
[12-12-04 14:15:12.485] {main} Linux 3.2.27+ arm
[12-12-04 14:15:12.489] {main} Java(TM) SE Embedded Runtime Environment 1.7.0_06-b24, UTF-8, en
[12-12-04 14:15:12.493] {main} Java HotSpot(TM) Embedded Client VM 23.2-b09, 32, mixed mode, Oracle Corporation

Cool!

Trying http://raspberrypi:8080/

500 Servlet Exception

javac compiler is not available in Java(TM) SE Embedded Runtime Environment
1.7.0_06-b24. Check that you are using the JDK, not the JRE.

Well that's expect also, we're using a JRE so no JSP compiler...

Trying http://raspberrypi:8080/resin-doc/ That works! Why?... XTP is not compiled!

Trying http://raspberrypi:8080/resin-admin That works too! PHP is not compiled either!