In-circuit emulation (ICE) is the use of a hardware device or in-circuit emulator used to

debug In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve i ...

the

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...

of an

embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded ...

. 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

JTAG JTAG (named after the Joint Test Action Group which codified it) is an industry standard for verifying designs and testing printed circuit boards after manufacture. JTAG implements standards for on-chip instrumentation in electronic design aut ...

-based hardware debuggers which provide equivalent access using

on-chip debugging 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 car ...

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 A misnomer is a name that is incorrectly or unsuitably applied. Misnomers often arise because something was named long before its correct nature was known, or because an earlier form of something has been replaced by a later form to which the name ...

, sometimes confusingly so, because emulation is no longer involved. Embedded systems present special problems for programmers because they usually lack keyboards, monitors,

disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...

s 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 A central processing unit (CPU), also called a central processor, main processor or just Processor (computing), processor, is the electronic circuitry that executes Instruction (computing), instructions comprising a computer program. The CPU per ...

(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 A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

(PC) to the embedded system. The terminal or PC provides an interactive

user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...

for the programmer to investigate and control the embedded system. For example, it is routine to have a source code level

debugger A debugger or debugging tool is a computer program used to test and debug other programs (the "target" program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its executi ...

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

bricked A brick (or bricked device) is a mobile device, game console, router or other consumer electronic device that is no longer functional due to corrupted firmware, a hardware problem, or other damage. The term analogizes the device to a brick's ...

. Embedded systems often lack basic functions to detect signs of software failure, such as a

memory management unit A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical a ...

(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

breakpoint In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause. More generally, a breakpoint is a means of acquiring know ...

s, 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.

Advantages

Virtually all embedded systems have a hardware element and a software element, which are separate but tightly interdependent. The ICE allows the software element to be run and tested on the hardware on which it is to run, but still allows programmer conveniences to help isolate faulty code, such as ''source-level debugging'' (which shows a program as it was originally written) and ''single-stepping'' (which lets programmers run programs step-by-step to find errors). Most ICEs consist of an adaptor unit that sits between the ICE host computer and the system to be tested. A

pin header A pin header (or simply header) is a form of electrical connector. A male pin header consists of one or more rows of metal pins molded into a plastic base, often apart, though available in many spacings. Male pin headers are cost-effective du ...

and cable assembly connects the adaptor to a socket where the actual

(CPU) or microcontroller mounts within the embedded system. Recent ICEs enable programmers to access the on-chip debug circuit that is integrated into the CPU via JTAG or

background debug mode interface Background debug mode (BDM) interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers. It requires a single wire and specialized electronics ...

(BDM) to debug the software of an embedded system. These systems often use a standard version of the CPU chip, and can simply attach to a debug port on a production system. They are sometimes called in-circuit debuggers or ICDs, to distinguish the fact that they do not replicate the functionality of the CPU, but instead control an already existing, standard CPU. Since the CPU need not be replaced, they can operate on production units where the CPU is soldered in and cannot be replaced. On x86 Pentiums, a special 'probe mode' is used by ICEs to aid in debugging. In the context of embedded systems, the ICE is not emulating hardware. Rather, it is providing direct debug access to the actual CPU. The system under test is under full control, allowing the developer to load, debug and test code directly. Most host systems are ordinary commercial computers unrelated to the CPU used for development. For example, a

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...

PC might be used to develop software for a system using a Freescale 68HC11 chip, a processor that cannot run Linux. The programmer usually edits and compiles the embedded system's code on the host system, as well. The host system will have special compilers that produce executable code for the embedded system, termed

cross compiler A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is running. For example, a compiler that runs on a PC but generates code that runs on an Android smartphone is a cross c ...

s or cross

assemblers Assembler may refer to: Arts and media * Nobukazu Takemura, avant-garde electronic musician, stage name Assembler * Assemblers, a fictional race in the ''Star Wars'' universe * Assemblers, an alternative name of the superhero group Champions of A ...

On-chip debugging

''On-chip debugging'' is an alternative to in-circuit emulation. It uses a different approach to address a similar goal. On-chip debugging, often loosely termed as ''Joint Test Action Group'' (JTAG), uses the provision of an additional debugging interface to the live hardware, in the production system. It provides the same features as in-circuit debugging, such as inspection of internal state or variables and may have the ability to set checkpoints, breakpoints and watchpoints. The difference is that this is provided by additional silicon within the production processor, rather than swapping the processor for an off-board debugging emulator. For this reason, some of the functions of the ICE is changed by the specifications of the processor. An additional JTAG interface is added to the controller board, and this is required on every production system, but as this only requires a few signal pins the extra cost is minimal. JTAG interfaces were originally developed for, and are still useful for, end of production testing.

Intel

To support in-circuit emulator (ICE) debugging on Intel 286, five additional pins were available on the processor: one input pin to externally force an ICE breakpoint, (ICEBP#) and two alternative pairs of output pins to select operations via the ICE-bus instead of user memory. "User bus cycle status signals, S1# and S0# support the user's bus and ICE bus cycle status signals, ICES1# and ICES0# support the ICE bus. … The ICE bus is used only for Data Read, Code Read, Halt, Shutdown, and Memory Write cycles. … microprocessor is forced to compatible mode at reset, … it cannot be switched back to compatible mode except by reset (or ICE breakpoint), … ICE must be given special attention since it is the only case in which a switch of the master microprocessor from protection mode to compatibility mode can occur (except for reset). … ICE software begins execution following an ICE breakpoint in compatibility mode and then switches to protection mode for the bulk of its operations." On the 80286 two instructions (0F 04, 0F 05) exist to dump/restore the complete CPU state to memory offset 0x800, along with a single-byte override prefix (F1) to enable ICE-mode to access user-memory.

References

External links