Build Recipe: OpenWRT

OpenWRT is a Linux platform for embedded devices like routers. Originally OpenWRT was based on Wi-Fi routers from Linksys. Then it was extended to support Broadcom (MIPS) SoC chipsets and now it even supports non-MIPS devices. Because it provides platform support for connected embedded devices, OpenWRT is a natural and useful example to illustrate how easy it is to adapt Java ME technology to Linux-based network devices.

These notes describe how to build phoneME Advanced Foundation Profile for the OpenWRT platform.

Platform Notes

OpenWRT has many useful features for an embedded software platform including a simple package management system (IPKG), a template-based build system for generating ROM images as well as target toolchains. The OpenWRT runtime software includes many modern embedded software features:

• 2.6 Linux kernel
• uClibc, a small-footprint POSIX library
• BusyBox, a shared binary for common UNIX utilities
• JFFS2, a read/write Flash ROM-oriented filesystem
• SquashFS, a read-only Flash ROM-oriented filesystem
• Itsy Package Management System (IPKG), an embedded package management system
• X-WRT, a web management console

As a platform, OpenWRT provides several core and optional network services and applications. For example,

• dnsmasq, a DNS forwarder and DHCP server
• iptables, a packet filtering firewall system
• dropbear, a lightweight SSH client and server
• various web servers
• NFS & Samba support
• USB support

Many of these services and applications are available through the IPKG package management system. Some, like NFS and USB support, require optional kernel modules.

Note: OpenWRT has two major versions: the more recent Kamikaze version supports the Linux 2.6 kernel and a wider variety of chipsets and devices and the now legacy White Russian version supports the Linux 2.4 kernel and mostly Broadcom chipsets. These notes cover the Kamikaze version of OpenWRT.

Build System Setup

Required Developer Tools

OpenWRT has a powerful build system that compiles its own toochain for a target platform. That means that when OpenWRT adds support for a new device it includes the procedures for configuring and building a gcc-based toolchain for cross-compiling. In fact, OpenWRT can build a relocatable SDK for a specific target. As we will see, this makes build system setup much easier for phoneME Advanced.

Note: The only non-standard OpenWRT package required by phoneME Advanced is libpthread.

Note: The OpenWRT toolchain is built by the OpenWRT build system and located in build_dir/mipsel/OpenWrt-SDK-brcm47xx-for-Linux-i686 in the OpenWRT distribution layout. While it should also be possible to use the standalone OpenWRT SDK from downloads.openwrt.org, the versions there are somewhat out of date and when building from trunk it's better to build with a more up to date version of the SDK.

Required Project Components

After installing and updating the required developer tools for the CDC build system, you can get the project source code by either downloading the project source code bundle (appropriate for evaluation purposes) or checking out the project source code from the repository. These procedures are described in Getting the Project Source Code.

The required phoneME Advanced project components for building Foundation Profile are:

• cdc
• tools

Building phoneME Advanced

Create a build driver script and make it executable

The following script builds a basic Foundation Profile target:

#!/bin/sh
make                                                 \
  J2ME_CLASSLIB=foundation                           \
  CVM_JIT=true                                       \
  CVM_OPTIMIZED=true                                 \
  CVM_PRELOAD_LIB=true                               \
  CVM_BUILD_SUBDIR_NAME=cdc-fp \
  JDK_HOME=/usr/java/j2sdk1.4.2_15/bin/ \
  CVM_TARGET_TOOLS_PREFIX=/home/developer/openwrt/build_dir/\
mipsel/OpenWrt-SDK-brcm47xx-for-Linux-i686/staging_dir/\
toolchain-mipsel_gcc4.1.2/bin/mipsel-linux-uclibc-

After modifying this script it can be invoked as follows:

$ sh < build-fp.sh >& err &

Create the CDC IPKG archive

1. Create a directory for staging the CDC IPKG archive.

   $ export OPENWRT_PACKAGE_DIR=$OPENWRT_DIR/build_dir/mipsel/OpenWrt-SDK-brcm47xx-for-Linux-i686/package/cdc
   $ mkdir $OPENWRT_PACKAGE_DIR
   

2. Stage the layout for the CDC IPKG archive with the following hierarchy:

   Makefile
   files/
     usr/
       java/
         cdc/
           democlasses.jar
           testclasses.zip
           bin/
             cvm
           lib/
             ...
   

   • files is a directory that contains the runtime files for the package.

   • Makefile drives the packaging process by the OpenWRT SDK:

     include $(TOPDIR)/rules.mk
     
     PKG_NAME:=pmea-fp
     PKG_VERSION:=1_1_2
     PKG_RELEASE:=b04
     PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)
     
     include $(INCLUDE_DIR)/package.mk
     
     define Package/pmea-fp
       SUBMENU:=Java
       SECTION:=lang
       CATEGORY:=Languages
       DEPENDS:=+libpthread
       TITLE:=CDC Java runtime environment
     endef
     
     define Package/pmea-fp/description
       phoneME is an open source project based on Java Micro Edition (Java ME) \
       technology. phoneME Advanced is a phoneME project based on Java ME CDC \
       technology targeting resource-constrained devices like smartphones, \ 
       set-top boxes and office equipment. See https://phoneme.dev.java.net \ 
       and http://java.sun.com/products/cdc
     endef
     
     define Build/Compile
     endef
     
     define Package/pmea-fp/install
     	$(INSTALL_DIR) $(1)/usr/java/cdc
     	$(CP) files/usr/java/cdc $(1)/usr/java
     endef
     
     $(eval $(call BuildPackage,pmea-fp))
     

3. Copy the files that are generated by the CDC build system to the staging directory:

   $ cd pmea-fp
   $ cp -r bin lib democlasses.jar testclasses.zip $OPENWRT_PACKAGE_DIR
   

4. Build the CDC IPKG archive:

   $ cd OpenWrt-SDK-brcm47xx-for-Linux-i686
   $ make
   

   The new CDC package is in OpenWrt-SDK-Linux-i686-1/bin/packages/mipsel/pmea-fp_1_1_2-b04_mipsel.ipk.

Runtime Examples

After the build process successfully finishes, the CDC Java runtime environment is available as runtime executable located in a few target directories, most importantly the bin and lib directories.

1. Copy the CDC package to the device:

   $ scp OpenWrt-SDK-Linux-i686-1/bin/packages/mipsel/pmea-fp_1_1_2-b04_mipsel.ipk root@192.168.1.1:/tmp
   

2. Remotely login to the target device:

   $ ssh root@192.168.1.1
   

3. Install the CDC package:

   $ ipkg install /tmp/pmea-fp_1_1_2-b04_mipsel.ipk
   

4. Run a test program:

   $ /usr/java/cdc/bin/cvm -cp /usr/java/cdc/testclasses.zip Test