Program animation

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Program animation or Stepping refers to the now very common debugging method of executing code one “line” at a time. The programmer may examine the state of the program, machine, and related data before and after execution of a particular line of code. This allows evaluation of the effects of that statement or instruction in isolation and thereby gain insight into the behavior (or misbehavior) of the executing program. Nearly all modern IDEs and debuggers support this mode of execution. Some testing tools allow programs to be executed step-by-step optionally at either source code level or machine code level depending upon the availability of data collected at compile time.

Contents

1 History
2 Techniques for program animation
3 Comparison of methods

3.1 Additional features

4 Examples of program animators
5 External links and references
6 References

History[edit]

System/360 (Model 65) operator’s console, with register value lamps and toggle switches and buttons (middle of picture) .

Instruction stepping or single cycle also referred to the related, more microscopic, but now obsolete[dubious – discuss] method of debugging code by stopping the processor clock and manually advancing it one cycle at a time. For this to be possible, three things are required:

A control that allows the clock to be stopped (e.g. a “Stop” button).
A second control that allows the stopped clock to be manually advanced by one cycle (e.g. An “instruction step” switch and a “Start” button).
Some means of recording the state of the processor after each cycle (e.g. register and memory displays).

On the IBM System 360 processor range announced in 1964, these facilities were provided by front panel switches, buttons and banks of neon lights.
Other systems such as the PDP-11 provided similar facilities, again on some models. The precise configuration was also model-dependent. It would not be easy to provide such facilities on LSI processors such as the Intel x86 and Pentium lines, owing to cooling considerations[dubious – discuss][clarification needed].
As multiprocessing became more commonplace, such techniques would have limited practicality, since many independent processes would be stopped simultaneously. This led to the development of proprietary software from several independent vendors that provided similar features but deliberately restricted breakpoints and instruction stepping to particular application programs in particular addre
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