Keil arm compile RO RW ZI DATA

The composition of ARM program (referring to the program being executed in the ARM system, not the bin file saved in ROM) 
An ARM program consists of 3 parts: RO segment, RW segment and ZI segment 
RO is the instructions and constants in the program 
RW is the initialized variable in the program 
ZI is the uninitialized variable in the program 
From the above 3 points, it can be understood that: 
RO is readonly, 
RW is read/write, and 
ZI is zero 
The composition of ARM image file 
The so-called ARM image file refers to the bin file burned into ROM, also known as image file. It is called Image file below. 
Image file contains RO and RW data. 
The reason why Image file does not contain ZI data is that ZI data is all 0, so it is not necessary to include it. Just clear the area where ZI data is before running the program. Including it will waste storage space. 
Q: Why must Image contain RO and RW? 
A: Because the instructions and constants in RO and the initialized variables in RW cannot be "created out of nothing" like ZI.  From the above two points, we can know that the image file burned into ROM is not exactly the same as the ARM program in actual operation. Therefore, it is necessary to understand how the ARM program reaches the actual operation state from the image in ROM.
In  fact, the instructions in RO should at least have the following functions:  1. Move RW from ROM to RAM, because RW is a variable and variables cannot exist in ROM.  2. Clear all RAM areas where ZI is located, because the ZI area is not in the image, so the program needs to clear the corresponding RAM area according to the ZI address and size given by the compiler. ZI is also a variable. Similarly: variables cannot exist in ROM In the initial stage of program operation, the C program can access variables normally only after the instructions in RO complete these two tasks. Otherwise, only code without variables can be run.  After saying the above, you may still be a little confused. What are RO, RW and ZI? Below I will give a few examples to explain what RO, RW, and ZI mean in C in the most intuitive way.   1; RO  Look at the following two programs. There is a statement between them. This statement is to declare a character constant. So according to what we said before, they should only differ by one byte in RO data (character constants are 1 byte).  Prog1:  #include   void main(void)  {  ;  }  Prog2:  #include   const char a = 5；  void main(void)  {  ;  }  The compiled information of Prog1 is as follows:  ===========================================================================================  Code RO Data RW Data ZI Data Debug  948 60 0 96 0 Grand Totals  =====================================================================================  Total RO Size(Code + RO Data) 1008 ( 0.98kB)  Total RW Size(RW Data + ZI Data  ) 96 ( 0.09kB)  Total ROM Size(Code + RO Data + RW Data) 1008 ( 0.98kB)  === ...  ===================================================================  09  (  0.99kB  )  Total RW Size (RW Data + ZI Data) 96 ( 0.09kB)  Total ROM Size (Code + RO Data + RW  Data  )  1009  (  0.99kB  )  ===  ... 














































void main(void) 
{ 
; 
} 
Prog4: 
#include  
char a = 5； 
void main(void) 
{ 
; 
} 
The information after compiling Prog3 is as follows: 
======================================================================================= 
Code RO Data RW Data ZI Data Debug 
948 60 0 96 0 Grand Totals 
=============================================================================================================== 
Total RO Size(Code + RO Data) 1008 ( 0.98kB) 
Total RW Size(RW Data + ZI Data) 96 ( 0.09kB) 
Total ROM Size(Code + RO Data + RW Data) 1008 ( 0.98kB) 
=========================================================================================== 
The information compiled by Prog4 is as follows: 
====================================================================================================== 
Code RO Data RW Data ZI Data Debug 
948 60 1 96 0 Grand Totals 
============================================================================ 
Total RO Size(Code + RO Data) 1008 (0.98kB) 
Total RW Size(RW Data + ZI Data) 97 (0.09kB) 
Total ROM Size(Code + RO Data + RW Data) 1009 (0.99kB) 
=== 
... 
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Prog3: 
#include  
void main(void) 
{ 
; 
} 
Prog4: 
#include  
char a； 
void main(void) 
{ 
; 
} 
The information after compiling Prog3 is as follows: 
======================================================================================== 
Code RO Data RW Data ZI Data Debug 
948 60 0 96 0 Grand Totals 
====================================================================================== 
Total RO Size(Code + RO Data) 1008 ( 0.98kB)  Total RW Size(RW Data + ZI Data 
) 96 ( 0.09kB) 
Total ROM Size(Code + RO Data + RW Data) 1008 ( 0.98kB) 
=== ...  ===================================================================  08 ( 0.98kB  ) Total RW Size (RW Data + ZI Data)  97  (  0.09kB)  Total ROM Size (Code + RO Data + RW Data) 1008 (0.98kB) 








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Appendix: 
Program compilation command (assuming the C program is named tst.c): 
armcc -c -o tst.o tst.c 
armlink -noremove -elf -nodebug -info totals -info sizes -map -list aa.map -o tst.elf
The compiled information of tst.o is in the aa.map file. 
ROM mainly refers to: NAND Flash, Nor Flash 
RAM mainly refers to: PSRAM, SDRAM, SRAM, DDRAM