Книга: Real-Time Concepts for Embedded Systems
10.3.1 Internal Errors and Special Conditions Management
10.3.1 Internal Errors and Special Conditions Management
Handling and appropriately recovering from a wide range of errors without coming to a halt is often necessary in the application areas in which embedded systems are typically employed.
Exceptions are either error conditions or special conditions that the processor detects while executing instructions. Error conditions can occur for a variety of reasons. The embedded system might be implementing an algorithm, for example, to calculate heat exchange or velocity for a cruise control. If some unanticipated condition occurs that causes a division by zero, over-flow, or other math error, the application must be warned. In this case, the execution of the task performing the calculation halts, and a special exception service routine begins. This process gives the application an opportunity to evaluate and appropriately handle the error. Other types of errors include memory read or write failures (a common symptom of a stray pointer), or attempts to access floating-point hardware when not installed.
Many processor architectures have two modes of execution: normal and privileged. Some instructions, called privileged instructions, are allowed to execute only when the processor is in the privileged execution mode. An exception is raised when a privileged instruction is issued while the processor is in normal execution mode.
Special conditions are exceptions that are generated by special instructions, such as the TRAP instruction on the Motorola 68K processor family. These instructions allow a program to force the processor to move into privileged execution mode, consequently gaining access to a privileged instruction set. For example, the instruction used to disable external interrupts must be issued in privileged mode.
Another example of a special condition is the trace exception generated by the break point feature available on many processor architectures. The debugger agent, a special software program running on the embedded device, handles this exception, which makes using a host debugger to perform software break point and code stepping possible.
Although not all microcontrollers or embedded processors define the same types of exceptions or handle them in the same way, an exception facility is available and can assist the embedded systems engineer design a controlled response to these internal errors and special conditions.
Оглавление книги
- Разработка приложений баз данных InterBase на Borland Delphi
- Open Source Insight and Discussion
- Introduction to Microprocessors and Microcontrollers
- Chapter 6. Traversing of tables and chains
- Chapter 8. Saving and restoring large rule-sets
- Chapter 11. Iptables targets and jumps
- Chapter 5 Installing and Configuring VirtualCenter 2.0
- Chapter 16. Commercial products based on Linux, iptables and netfilter
- Appendix A. Detailed explanations of special commands
- Appendix B. Common problems and questions
- Appendix E. Other resources and links
- IP filtering terms and expressions