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In-circuit emulation (ICE) is the use of a hardware device or in-circuit emulator used to debug the software of an embedded system. It operates by using a processor with the additional ability to support debugging operations, as well as to carry out the main function of the system. Particularly for older systems, with limited processors, this usually involved replacing the processor temporarily with a hardware emulator: a more powerful although more expensive version. It was historically in the form of bond-out processor which has many internal signals brought out for the purpose of debugging. These signals provide information about the state of the processor. More recently the term also covers Joint Test Action Group (JTAG) based hardware debuggers which provide equivalent access using on-chip debugging hardware with standard production chips. Using standard chips instead of custom bond-out versions makes the technology ubiquitous and low cost, and eliminates most differences between the development and runtime environments. In this common case, the ''in-circuit emulator'' term is a misnomer, sometimes confusingly so, because emulation is no longer involved. Embedded systems present special problems for programmers because they usually lack keyboards, monitors, disk drives and other user interfaces that are present on computers. These shortcomings make in-circuit software debugging tools essential for many common development tasks. ==Function== An in-circuit emulator (ICE) 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 view and change data used by the system's software. An ''emulator'' gets its name because it emulates (imitates) the central processing unit (CPU) of the embedded system's computer. Traditionally it had a plug that inserts into the socket where the CPU integrated circuit chip would normally be placed. Most modern systems use the target system's CPU directly, with special JTAG-based debug access. Emulating the processor, or direct JTAG access to it, lets the ICE do anything that the processor can do, but under the control of a software developer. ICEs attach a computer terminal or personal computer (PC) to the embedded system. The terminal or PC provides an interactive user interface for the programmer to investigate and control the embedded system. For example, it is routine to have a source code level debugger with a graphical windowing interface that communicates through a JTAG adapter (emulator) to an embedded target system which has no graphical user interface. 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 memory management unit (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 section 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, in an attempt to identify the origin of a failure. Most modern microcontrollers use resources provided on the manufactured version of the microcontroller for device programming, emulating, and debugging features, instead of needing another special emulation-version (that is, bond-out) of the target microcontroller. Even though it is a cost-effective method, since the ICE unit only manages the emulation instead of actually emulating the target microcontroller, trade-offs must be made to keep prices low at manufacture time, yet provide enough emulation features for the (relatively few) emulation applications. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「In-circuit emulation」の詳細全文を読む スポンサード リンク
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