A Hardware Abstraction Layer in Java

Abstract

Embedded systems use specialized hardware devices to interact with their environment, and since they have to be dependable, it is attractive to use a modern, type-safe programming language like Java to develop programs for them. Standard Java, as a platform-independent language, delegates access to devices, direct memory access, and interrupt handling to some underlying operating system or kernel, but in the embedded systems domain resources are scarce and a Java Virtual Machine (JVM) without an underlying middleware is an attractive architecture. The contribution of this article is a proposal for Java packages with hardware objects and interrupt handlers that interface to such a JVM. We provide implementations of the proposal directly in hardware, as extensions of standard interpreters, and finally with an operating system middleware. The latter solution is mainly seen as a migration path allowing Java programs to coexist with legacy system components. An important aspect of the proposal is that it is compatible with the Real-Time Specification for Java (RTSJ).

An Evaluation of Safety-Critical Java on a Java Processor

“…The notion of the interrupt handler in SCJ and the mapping of lock priorities to interrupt disabling are similar to the proposal in [17]. In our current implementation the JVM accepts a standard Runnable as an interrupt handler, which is registered by a system class.…”

“…Similar to other MSOs, MISR objects have to be registered to a specific mission and the interrupt service routine (ISR) code is implemented by overriding the handle() method of RTSJ's InterruptServiceRoutine class, which in SCJ is more restricted than its RTSJ counterpart. In general, in Java an ISR can be implemented as a handler or as an event [17]. The handler approach uses a method invoked by the hardware while the event approach uses a form of asynchronous event to fire an AEH or unblock a managed thread.…”

“…The handler approach uses a method invoked by the hardware while the event approach uses a form of asynchronous event to fire an AEH or unblock a managed thread. The advantages and disadvantages of both methods are described in more detail in [17].…”

Hardware Support for Safety-Critical Java Scope Checks

“…The first is an application inspired in one of the examples presented in [13], where a probe containing certain sensors is used to scan the walls of a well. For our example, we have an application that periodically checks a set of artificial sensors simulated in hardware using hardware objects as described in [14]. The application creates an array of objects to hold the sensor's results in a scoped memory.…”

Hardware Support for Embedded Java

“…Another option is to use so called hardware objects [56], which represent I/O devices as plain Java objects. The hardware objects are platform specific (as I/O devices are), but the mechanism to represent I/O devices as Java objects can be implemented in any JVM.…”