ARM development experience! (Part 2)

/* 
********************************************************************************************************* 
* Programming Arm 
* 
* 
* (c) Copyright 1992-2008, Xi'an Jiaotong University 
* All Rights Reserved 
* 
* Institute of Automatic Control 158 
* 
* File: Serial 2 
* Version: V1.00 
* Author: Pan Ziqiang 
* 
* Object: ARM7 
* Mode: ARM 
* Tool: ADS1.20 
********************************************************************************************************** 
*/ 


4 Description file 
To write a description file, you must know the composition of the ARM Image file and the execution mechanism of the ARM Image file. 
4.1 Structure of ARM Image 
An ARM Image structure is defined by the linker in the following aspects: 
 The regions and output sections that make it up 
 The locations of these regions and sections in memory when the Image is downloaded 
 The locations of these regions and sections in memory when the Image is executed 
4.1.1 Composition of ARM Image 
An ARM Image is stored in an executable file, and its hierarchy may include Image, regions, output sections, and input sections. 
 An Image is composed of one or more regions, each of which includes one or more output sections 
 Each output section is composed of one or more input sections 
 Input sections are code and data information in an object file. 
The structure of an Image is shown in the figure 
below  :
1 Figure: tu1.JPG (24684 bytes) 
NOTE For the definitions of Input section, output section, and region, see page 3-3 of ADS_LinkerGuide. 
At the same time, the Input section has several attributes, namely readonly, read-write, and zero-initialized. They are called RO, RW, and ZI respectively. The attribute comes from the attr attribute after AREA. 
For example, CODE is RO, DATA is RW, and NOINT defaults to ZI, that is, it is initialized with a value of 0, but you can choose not to initialize it with a value of 0. The ZI attribute only comes from SPACE, DCB, DCD, DCDU, DCQ, DCQU, DCW, or DCWU. According to the above definition, the ZI attribute is included in the RW attribute, which is RW data with an initial value. For example, in C language, code is RO, static variables and global variables are RW and ZI.