JDSNET 2XLP Signum In-Circuit Emulator

An in-circuit emulator (ICE) also called on-circuit debugger (OCD) or background debug module (BDM) is a hardware device used to debug the software of an embedded system. Embedded systems present special problems for a programmer, because they usually lack keyboards, screens, disk-drives and other helpful user interfaces and storage devices that are present on business computers.

In-circuit emulation can also refer to the use of hardware emulation, when the emulator is plugged into a system (not always embedded) in place of a yet-to-be-built chip (not always a processor). These in-circuit emulators provide a way to run the system with "live" data while still allowing relatively good debugging capabilities.

The basic idea of an "in-circuit emulator" is that it provides a window into the embedded system. The programmer uses the emulator to load programs into the embedded system, run them, step through them slowly, and see and change the data used by the system's software.

An "emulator" gets its name because it often "emulates" the central processing unit of the embedded system's computer. Often, it literally has a plug that plugs into the same socket as the CPU chip. Emulating the main computer lets it do anything that the main computer can do, but under the control of a programmer.

ICEs are always tools that attach a terminal or PC to the embedded system. The terminal or PC provides an interactive user interface for the programmer to investigate and control the embedded system.

Notably, when their program fails, most embedded systems simply become inert lumps of nonfunctioning electronics. Embedded systems often lack basic functions to detect signs of software failure, such as an MMU to catch memory access errors. Without an ICE, the development of embedded systems can be extremely difficult, because there is usually no way to tell what went wrong. With an ICE, the programmer can usually test pieces of code, then isolate the fault to a particular failing piece of code, and then inspect the failing code and rewrite it to solve the problem.

In usage, an ICE provides the programmer with execution breakpoints, memory display and monitoring, and input/output control. Beyond this, the ICE can be programmed to look for any range of matching criteria to pause at, hopefully catching the failure's origin.