An introduction to memory

The need for communications between tasks depends upon your problem: You DON'T need communications:

An introduction to memory

Quick Reference The goal of this chapter is to write a complete char device driver. We'll develop a character driver because this class is suitable for most simple hardware devices. Char drivers are also easier to understand than, for example, block drivers or network drivers.

Our ultimate aim is to write a modularized char driver, but we won't talk about modularization issues in this chapter.

Throughout the chapter, we'll present code fragments extracted from a real device driver: A side effect of this behavior is that, as far as scull is concerned, the word device can be used interchangeably with "the memory area used by scull.

Anyone can compile and run scull, and scull is portable across the computer architectures on which Linux runs. On the other hand, the device doesn't do anything "useful" other than demonstrating the interface between the kernel and char drivers and allowing the user to run some tests.

The Design of scull The first step of driver writing is defining the capabilities the mechanism the driver will offer to user programs. Since our "device" is part of the computer's memory, we're free to do what we want with it.

It can be a sequential or random-access device, one device or many, and so on.


To make scull be useful as a template for writing real drivers for real devices, we'll show you how to implement several device abstractions on top of the computer memory, each with a different personality.

The scull source implements the following devices. Each kind of device implemented by the module is referred to as a type: Global means that if the device is opened multiple times, the data contained within the device is shared by all the file descriptors that opened it.

MUSCLE User Guide

Persistent means that if the device is closed and reopened, data isn't lost. One process reads what another process writes. If multiple processes read the same device, they contend for data. The internals of scullpipe will show how blocking and nonblocking read and writecan be implemented without having to resort to interrupts.

Although real drivers synchronize with their devices using hardware interrupts, the topic of blocking and nonblocking operations is an important one and is separate from interrupt handling covered in Chapter 9, "Interrupt Handling".

These variations of scull add more "policy" than "mechanism;" this kind of behavior is interesting to look at anyway, because some devices require types of management like the ones shown in these scull variations as part of their mechanism.

Each of the scull devices demonstrates different features of a driver and presents different difficulties. This chapter covers the internals of scull0 to skull3; the more advanced devices are covered in Chapter 5, "Enhanced Char Driver Operations": Major and Minor Numbers Char devices are accessed through names in the filesystem.

Table of Contents

Special files for char drivers are identified by a "c" in the first column of the output of ls -l. If you issue the ls -l command, you'll see two numbers separated by a comma in the device file entries before the date of last modification, where the file length normally appears.

These numbers are the major device number and minor device number for the particular device. The following listing shows a few devices as they appear on a typical system.

Their major numbers are 1, 4, 7, and 10, while the minors are 1, 3, 5, 64, 65, and The kernel uses the major number at open time to dispatch execution to the appropriate driver. The minor number is used only by the driver specified by the major number; other parts of the kernel don't use it, and merely pass it along to the driver.

It is common for a driver to control several devices as shown in the listing ; the minor number provides a way for the driver to differentiate among them. If this file system is used, management of device files is simplified and quite different; on the other hand, the new filesystem brings several user-visible incompatibilities, and as we are writing it has not yet been chosen as a default feature by system distributors.

The previous description and the following instructions about adding a new driver and special file assume that devfs is not present. The gap is filled later in this chapter, in "The Device Filesystem".This page contains Verilog tutorial, Verilog Syntax, Verilog Quick Reference, PLI, modelling memory and FSM, Writing Testbenches in Verilog, Lot of Verilog Examples and Verilog in One Day Tutorial. This article is a step by step guide for tuning and optimizing Red Hat Enterprise Linux on x86 and x platforms running Oracle 9i (32bit/64bit) and . Computer memory, device that is used to store data or programs (sequences of instructions) on a temporary or permanent basis for use in an electronic digital computer.

Computers represent information in binary code, written as sequences of 0s and 1s. Each binary digit (or “bit”) may be stored by.

An introduction to memory

This is the first tutorial in the "Livermore Computing Getting Started" workshop. It is intended to provide only a very quick overview of the extensive and broad topic of Parallel Computing, as a lead-in for the tutorials that follow it.

An introduction to memory

This is the first tutorial in the "Livermore Computing Getting Started" workshop. It is intended to provide only a very quick overview of the extensive and broad topic of Parallel Computing, as a lead-in for the tutorials that follow it.

This clear and accessible textbook introduces the brain's remarkable capacity for memory. The text was developed for undergraduate and beginning graduate students, but it will also be of use to cognitive scientists, biologists, and psychologists who seek an introduction to biological investigations of memory.

Introduction to Redis – Redis