Книга: Real-Time Concepts for Embedded Systems
10.3.2 Hardware Concurrency and Service Request Management
10.3.2 Hardware Concurrency and Service Request Management
The ability to perform different types of work simultaneously is important in embedded systems. Many external hardware devices can perform device-specific operations in parallel to the core processor. These devices require minimum intervention from the core processor. The key to concurrency is knowing when the device has completed the work previously issued so that additional jobs can be given. External interrupts are used to achieve this goal.
For example, an embedded application running on a core processor issues work commands to a device. The embedded application continues execution, performing other functions while the device tries to complete the work issued. After the work is complete, the device triggers an external interrupt to the core processor, which indicates that the device is now ready to accept more commands. This method of hardware concurrency and use of external interrupts is common in embedded design.
Another use of external interrupts is to provide a communication mechanism to signal or alert an embedded processor that an external hardware device is requesting service. For example, an initialized programmable interval timer chip communicates with the embedded processor through an interrupt when a preprogrammed time interval has expired. (Chapter 11 discusses programmable interval timers in detail.) Similarly, the network interface device uses an interrupt to indicate the arrival of packets after the received packets have been stored into memory.
The capabilities of exceptions and their close cousins, external interrupts, empower embedded designs. Applying the general exception facility to an embedded design, however, requires properly handling general exceptions according to the source and associated cause of each particular general exception in question. The following section provides the needed background knowledge.
- 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