Книга: Real-Time Concepts for Embedded Systems
10.2 What are Exceptions and Interrupts?
10.2 What are Exceptions and Interrupts?
An exception is any event that disrupts the normal execution of the processor and forces the processor into execution of special instructions in a privileged state. Exceptions can be classified into two categories: synchronous exceptions and asynchronous exceptions.
Exceptions raised by internal events, such as events generated by the execution of processor instructions, are called synchronous exceptions. Examples of synchronous exceptions include the following:
· On some processor architectures, the read and the write operations must start at an even memory address for certain data sizes. Read or write operations that begin at an odd memory address cause a memory access error event and raise an exception (called an alignment exception).
· An arithmetic operation that results in a division by zero raises an exception.
Exceptions raised by external events, which are events that do not relate to the execution of processor instructions, are called asynchronous exception s. In general, these external events are associated with hardware signals. The sources of these hardware signals are typically external hardware devices. Examples of asynchronous exceptions include the following:
· Pushing the reset button on the embedded board triggers an asynchronous exception (called the system reset exception).
· The communications processor module that has become an integral part of many embedded designs is another example of an external device that can raise asynchronous exceptions when it receives data packets.
An interrupt, sometimes called an external interrupt, is an asynchronous exception triggered by an event that an external hardware device generates. Interrupts are one class of exception. What differentiates interrupts from other types of exceptions, or more precisely what differentiates synchronous exceptions from asynchronous exceptions, is the source of the event. The event source for a synchronous exception is internally generated from the processor due to the execution of some instruction. On the other hand, the event source for an asynchronous exception is an external hardware device.
Because the term interrupt has been used extensively in other texts, therefore, the text that follows uses exceptions to mean synchronous exceptions and interrupts to mean asynchronous exceptions. The book uses general exceptions to mean both. The term interrupts and external interrupts are used interchangeably throughout the text.
Exceptions and interrupts are the necessary evils that exist in the majority of embedded systems. This facility, specific to the processor architecture, if misused, can become the source of troubled designs. While exceptions and interrupts introduce challenging design complications and impose strict coding requirements, they are nearly indispensable in embedded applications. The following sections describe the most common and important uses of these mechanisms.
Оглавление книги
- Shared Cache file
- 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