In-circuit emulator
Encyclopedia
An in-circuit emulator (ICE) is a hardware device used to debug
the software of an embedded system
. It was historically in the form of bond-out processor which has many internal signals brought out for the purpose of debugging. These signals provided information about the state of the processor.
More recently the term also covers 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 a programmer because they usually lack keyboard
s, 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.
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. It can be useful to compare this with an in-target probe
(ITP) sometimes used on enterprise servers.
An "emulator" gets its name because it emulates (imitates) the central processing unit
of the embedded system's computer. Traditionally it had a plug that inserts into the socket where the CPU 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 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. 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 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
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 the failure.
Some recent ICE developments (Microchip MPLAB
REAL ICE) utilize resources provided on the manufactured version of the microcontroller
for emulation 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 have to be made in order to keep the prices low at manufacture time, yet provide enough emulation features for the (relatively few) emulation applications.
Most ICEs consist of an adaptor unit that sits between the ICE host computer and the system to be tested. A header and cable assembly connects the adaptor to a socket where the actual CPU
or microcontroller
mounts within the embedded system. Recent ICEs enable a programmer to access the on-chip debug circuit that is integrated into the CPU via JTAG or BDM
(Background Debug Mode) in order 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 does not have to be replaced, they can operate on production units where the CPU is soldered in and cannot be replaced. An example is Microchip Technology
's ICD, which interfaces with most recent PIC microcontroller
s to debug software by attaching to the PIC's In-circuit programming/debugging port. On x86 Pentiums, a special 'probe mode' is used by ICEs to aid in debugging.
The ICE emulates the CPU. From the system's point of view, it has a real processor fitted, but from the programmer's point of view 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
PC
might be used to develop software for a system using a Freescale 68HC11
chip, which itself could not 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. These are called cross compiler
s or cross assemblers.
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
the software of an embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
. It was historically in the form of bond-out processor which has many internal signals brought out for the purpose of debugging. These signals provided information about the state of the processor.
More recently the term also covers 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
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
, sometimes confusingly so, because emulation is no longer involved.
Embedded systems present special problems for a programmer because they usually lack keyboard
Keyboard (computing)
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
s, 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.
In-circuit emulation can also refer to the use of hardware emulation
Hardware emulation
In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware with another piece of hardware, typically a special purpose emulation system. The emulation model is usually based on RTL source code, which is compiled into the format...
, 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. It can be useful to compare this with an in-target probe
In-target probe
In-target probe', or ITP is a device used in computer hardware and microprocessor design, to control a target microprocessor or similar ASIC at the register level. It generally allows full control of the target device and allows the computer engineer access to individual registers, program counter,...
(ITP) sometimes used on enterprise servers.
Function
An in-circuit emulator 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
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
of the embedded system's computer. Traditionally it had a plug that inserts into the socket where the CPU chip
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
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 terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
or PC to the embedded system. The terminal or PC provides an interactive user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...
for the programmer to investigate and control the embedded system. For example, it is routine to have a source code level debugger
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
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
Software bug
A software bug is the common term used to describe an error, flaw, mistake, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program's...
, such as an MMU
Memory management unit
A memory management unit , sometimes called paged memory management unit , is a computer hardware component responsible for handling accesses to memory requested by the CPU...
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
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....
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 the failure.
Some recent ICE developments (Microchip MPLAB
MPLAB
MPLAB Integrated Development Environment is a free, integrated toolset for the development of embedded applications on Microchip's PIC and dsPIC microcontrollers.- MPLAB IDE v8 :...
REAL ICE) utilize resources provided on the manufactured version of the microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
for emulation 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 have to be made in order to keep the 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 actual hardware on which it is to run, but still allows programmer conveniences to help isolate faulty code, such as "source-level debugging" (which shows the program the way the programmer wrote it) and single-stepping (which lets the programmer run the program 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 header and cable assembly connects the adaptor to a socket where the actual CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
or microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
mounts within the embedded system. Recent ICEs enable a programmer to access the on-chip debug circuit that is integrated into the CPU via JTAG or BDM
Background Debug Mode interface
Background Debug Mode interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers...
(Background Debug Mode) in order 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 does not have to be replaced, they can operate on production units where the CPU is soldered in and cannot be replaced. An example is Microchip Technology
Microchip Technology
Microchip Technology is an American manufacturer of microcontroller, memory and analog semiconductors. Its products include microcontrollers , Serial EEPROM devices, Serial SRAM devices, KEELOQ devices, radio frequency devices, thermal, power and battery management analog devices, as well as...
's ICD, which interfaces with most recent PIC microcontroller
PIC microcontroller
PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division...
s to debug software by attaching to the PIC's In-circuit programming/debugging port. On x86 Pentiums, a special 'probe mode' is used by ICEs to aid in debugging.
The ICE emulates the CPU. From the system's point of view, it has a real processor fitted, but from the programmer's point of view 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
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
PC
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
might be used to develop software for a system using a Freescale 68HC11
Freescale 68HC11
The 68HC11 is an 8-bit microcontroller family introduced by Motorola in 1985. Now produced by Freescale Semiconductor, it descended from the Motorola 6800 microprocessor. It is a CISC microcontroller...
chip, which itself could not 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. These are called cross compiler
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 run. Cross compiler tools are used to generate executables for embedded system or multiple platforms. It is used to compile for a platform upon which it is not feasible to...
s or cross assemblers.
See also
- Joint Test Action Group
- Background Debug Mode interfaceBackground Debug Mode interfaceBackground Debug Mode interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers...
- Hardware-assisted virtualization
- SoftICESoftICESoftICE is a kernel mode debugger for Microsoft Windows. Crucially, it is designed to run underneath Windows such that the operating system is unaware of its presence. Unlike an application debugger, SoftICE is capable of suspending all operations in Windows when instructed...