May 2004, Issue 166

Embedded Java Controllers

JAVA PACKAGES

Because an aJile processor is a microcontroller, you need access to the low-level parts of the controller. Just as it is necessary to use low-level registers on standard microcontrollers, it is necessary to do the same with the aJile processors. Hence, aJile wrote a number of packages to deal with the controller at the device level.

The com.ajile.components package contains various hardware components, including timers, triggers, and debounced buttons. com.ajile.events includes events specific to the aJile processors. The com.ajile.io package adds BufferedInputStream, BufferedOutputStream, and BufferedReader to the CLDC java.io package.

com.ajile.jem is the lowest level package. By using the rawJEM class, you can deal with memory locations and registers. The package also contains the PeriodicThread and PianoRoll classes, which are used later in this article.

Because the CLDC doesn’t include the Float, Double, and Math classes, they are added in com.ajile.lang, along with some Error classes. com.ajile. drivers.irq is the interrupt handler framework. The com.ajile.drivers.flash package contains the methods needed to read and write directly to the flash memory of the JStamp/JStik.

I find the com.ajile.drivers.gpio package to be the most useful. It is used to deal with low-level I/O ports and pins via high-level objects.

The com.ajile.drivers.gptc package is used to access the general-purpose timer/counters and the waveform module. The waveform module is a low-level part of the aJile chip, which can be used to generate arbitrary digital waveforms.

com.ajile.drivers.i2c has a driver to communicate via I2C. com.ajile.drivers. rtc.DS1305 provides support for the internal real-time clock chip, while com.ajile.drivers.RX5C62 provides support for the calendar chip.

com.ajile.drivers.spi has a driver to communicate via SPI. The com.ajile.file system package supports the accessing of the file systems available to the aJile chips. (Currently, these are only flash memory file systems.)

com.ajile.bootloader is an interface that allows a program to be loaded into a separate JVM. com.ajile.util contains a class, PropUtils, which allows access to system properties.

com.ajile.microedition.io contains the MemoryEfficientConnector class. This is an implementation of the java.microedition.io connector interface. com.ajile.net.util is a package containing network utility classes. com.ajile.net.dns provides basic access to domain name service. And, finally, note that com.ajile.net.sntp is a package for dealing with the simple network time protocol.

In order to have the advantages of preemptive threading, aJile, which wrote the Java libraries and tools for these controllers, has provided the PeriodicThread class to allow fully preemptive threading for time-critical items. The PeriodicThread can be a bit tricky to use until you get the hang of it. It uses the PianoRoll feature of the controller in order to run the PeriodicThread at intervals.