Книга: Real-Time Concepts for Embedded Systems
12.1 Introduction
12.1 Introduction
All embedded systems include some form of input and output (I/O) operations. These I/O operations are performed over different types of I/O devices. A vehicle dashboard display, a touch screen on a PDA, the hard disk of a file server, and a network interface card are all examples of I/O devices found in embedded systems. Often, an embedded system is designed specifically to handle the special requirements associated with a device. A cell phone, pager, and a handheld MP3 player are a few examples of embedded systems built explicitly to deal with I/O devices.
I/O operations are interpreted differently depending on the viewpoint taken and place different requirements on the level of understanding of the hardware details.
From the perspective of a system software developer, I/O operations imply communicating with the device, programming the device to initiate an I/O request, performing actual data transfer between the device and the system, and notifying the requestor when the operation completes. The system software engineer must understand the physical properties, such as the register definitions, and access methods of the device. Locating the correct instance of the device is part of the device communications when multiple instances of the same device are present. The system engineer is also concerned with how the device is integrated with rest of the system. The system engineer is likely a device driver developer because the system engineer must know to handle any errors that can occur during the I/O operations.
From the perspective of the RTOS, I/O operations imply locating the right device for the I/O request, locating the right device driver for the device, and issuing the request to the device driver. Sometimes the RTOS is required to ensure synchronized access to the device. The RTOS must facilitate an abstraction that hides both the device characteristics and specifics from the application developers.
From the perspective of an application developer, the goal is to find a simple, uniform, and elegant way to communicate with all types of devices present in the system. The application developer is most concerned with presenting the data to the end user in a useful way.
Each perspective is equally important and is examined in this chapter. This chapter focuses on:
· basic hardware I/O concepts,
· the structure of the I/O subsystem, and
· a specific implementation of an I/O subsystem.
Оглавление книги
- Introduction to Microprocessors and Microcontrollers
- Introduction
- 5.1 Introduction
- Introduction to Serial Devices
- 14.1 Introduction
- Introduction to PHP
- 3.4.1. Introduction to Atomic Transactions
- 11.1. Introduction to BusyBox
- 1.1 Introduction
- 2.5.1. Introduction to Group Communication
- 4.1.1. Introduction to Threads
- 6.1. INTRODUCTION