Hello!
So I was working on a project and I want to use the remained chunk of ram as backup storage for data representing electrical behavior in an IOT device I'm making.
following the next part is just to illustrate my question :
Stack_Size EQU 0x00007830
AREA STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem SPACE Stack_Size
__initial_sp
; <h> Heap Configuration
; <o> Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>
Heap_Size EQU 0x000007D0
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
#include <stdio.h>
int x=5;
void SystemInit(void)
{ }
int main(void)
{
char d=5;
}
Program Size: Code=532 RO-data=636 RW-data=0 ZI-data=32864
so I wanted to use everything available with the ram so in start up file I allocat3d ( 30768 byte in stack (0x7830) ... 2000 byte in Heap (0x7D0) )
1- first question is this the way to tell the compiler that I can use the 32k ram??
2-then why is the RW-data =0? I already defined and initiated a local and a global variables here which is supposed to be saved in the stack right? and RW-data represents the data in RAM right?
3- if I allocate 0 stack and 0 heap in startup file i still see +500 byte ZI data where do they come from? and how could ZI data in the example exceed the vaslue of 32768 which is the total capacity of RAM ? maybe the compiler Zero initialize some data in the Flash ROM?
basically how to know what data represents the RAM and what data represents the ROM? I know that Code is saved in ROM, RO-data is also saved in ROM, RW-data all saved in RAM, ZI-data could be saved in both I think. also in the map file I saw this
<strong>" Total RW Size (RW Data + ZI Data) 32864 ( 32.09kB)" </strong>
4-so it means maybe RW data could be saved in the flash? and how could RW data exceed 32kB when I declared only 2 variables and didn't allocate extra ram in startup file?
in the next figure :
<strong>Memory Map of the image
Image Entry point : 0x000002ed
Load Region LR_1 (Base: 0x00000000, Size: 0x00000490, Max: 0xffffffff, ABSOLUTE)
Execution Region ER_RO (Base: 0x00000000, Size: 0x00000490, Max: 0xffffffff, ABSOLUTE)
Base Addr Size Type Attr Idx E Section Name Object
0x00000000 0x0000026c Data RO 3 RESET startup_tm4c123.o
0x0000026c 0x00000008 Code RO 34 * !!!main c_w.l(__main.o)
0x00000274 0x00000034 Code RO 188 !!!scatter c_w.l(__scatter.o)
0x000002a8 0x0000001c Code RO 190 !!handler_zi c_w.l(__scatter_zi.o)
0x000002c4 0x00000002 Code RO 61 .ARM.Collect$$libinit$$00000000 c_w.l(libinit.o)
0x000002c6 0x00000000 Code RO 68 .ARM.Collect$$libinit$$00000002 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 71 .ARM.Collect$$libinit$$00000008 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 73 .ARM.Collect$$libinit$$0000000A c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 75 .ARM.Collect$$libinit$$0000000C c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 78 .ARM.Collect$$libinit$$0000000F c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 80 .ARM.Collect$$libinit$$00000011 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 82 .ARM.Collect$$libinit$$00000013 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 84 .ARM.Collect$$libinit$$00000015 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 86 .ARM.Collect$$libinit$$00000017 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 88 .ARM.Collect$$libinit$$00000019 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 90 .ARM.Collect$$libinit$$0000001B c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 92 .ARM.Collect$$libinit$$0000001D c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 94 .ARM.Collect$$libinit$$0000001F c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 96 .ARM.Collect$$libinit$$00000021 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 98 .ARM.Collect$$libinit$$00000023 c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 102 .ARM.Collect$$libinit$$0000002A c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 104 .ARM.Collect$$libinit$$0000002C c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 106 .ARM.Collect$$libinit$$0000002E c_w.l(libinit2.o)
0x000002c6 0x00000000 Code RO 108 .ARM.Collect$$libinit$$00000030 c_w.l(libinit2.o)
0x000002c6 0x00000002 Code RO 109 .ARM.Collect$$libinit$$00000031 c_w.l(libinit2.o)
0x000002c8 0x00000002 Code RO 129 .ARM.Collect$$libshutdown$$00000000 c_w.l(libshutdown.o)
0x000002ca 0x00000000 Code RO 143 .ARM.Collect$$libshutdown$$00000003 c_w.l(libshutdown2.o)
0x000002ca 0x00000000 Code RO 146 .ARM.Collect$$libshutdown$$00000006 c_w.l(libshutdown2.o)
0x000002ca 0x00000000 Code RO 149 .ARM.Collect$$libshutdown$$00000009 c_w.l(libshutdown2.o)
0x000002ca 0x00000000 Code RO 151 .ARM.Collect$$libshutdown$$0000000B c_w.l(libshutdown2.o)
0x000002ca 0x00000000 Code RO 154 .ARM.Collect$$libshutdown$$0000000E c_w.l(libshutdown2.o)
0x000002ca 0x00000002 Code RO 155 .ARM.Collect$$libshutdown$$0000000F c_w.l(libshutdown2.o)
0x000002cc 0x00000000 Code RO 36 .ARM.Collect$$rtentry$$00000000 c_w.l(rtentry.o)
0x000002cc 0x00000000 Code RO 38 .ARM.Collect$$rtentry$$00000002 c_w.l(rtentry2.o)
0x000002cc 0x00000006 Code RO 50 .ARM.Collect$$rtentry$$00000004 c_w.l(rtentry4.o)
0x000002d2 0x00000000 Code RO 40 .ARM.Collect$$rtentry$$00000009 c_w.l(rtentry2.o)
0x000002d2 0x00000004 Code RO 41 .ARM.Collect$$rtentry$$0000000A c_w.l(rtentry2.o)
0x000002d6 0x00000000 Code RO 43 .ARM.Collect$$rtentry$$0000000C c_w.l(rtentry2.o)
0x000002d6 0x00000008 Code RO 44 .ARM.Collect$$rtentry$$0000000D c_w.l(rtentry2.o)
0x000002de 0x00000002 Code RO 65 .ARM.Collect$$rtexit$$00000000 c_w.l(rtexit.o)
0x000002e0 0x00000000 Code RO 111 .ARM.Collect$$rtexit$$00000002 c_w.l(rtexit2.o)
0x000002e0 0x00000004 Code RO 112 .ARM.Collect$$rtexit$$00000003 c_w.l(rtexit2.o)
0x000002e4 0x00000006 Code RO 113 .ARM.Collect$$rtexit$$00000004 c_w.l(rtexit2.o)
0x000002ea 0x00000002 PAD
0x000002ec 0x00000118 Code RO 4 * .text startup_tm4c123.o
0x00000404 0x00000008 Code RO 10 .text main.o
0x0000040c 0x00000006 Code RO 32 .text c_w.l(heapauxi.o)
0x00000412 0x0000004a Code RO 52 .text c_w.l(sys_stackheap_outer.o)
0x0000045c 0x0000000c Code RO 54 .text c_w.l(exit.o)
0x00000468 0x00000008 Code RO 62 .text c_w.l(libspace.o)
0x00000470 0x0000000c Code RO 121 .text c_w.l(sys_exit.o)
0x0000047c 0x00000002 Code RO 132 .text c_w.l(use_no_semi.o)
0x0000047e 0x00000000 Code RO 134 .text c_w.l(indicate_semi.o)
0x0000047e 0x00000002 PAD
0x00000480 0x00000010 Data RO 186 Region$$Table anon$$obj.o</strong>
As far I know, the ROM starts with 0x0 and here last used address is 0x480 and size is (0x490= 1168 bytes) which confirms the size of ROM mentioned in the last section of .map file
so if we follow same concept here
Execution Region ER_RW (Base: 0x20000000, Size: 0x00000000, Max: 0xffffffff, ABSOLUTE)
**** No section assigned to this execution region ****
Execution Region ER_ZI (Base: 0x20000000, Size: 0x00008060, Max: 0xffffffff, ABSOLUTE)
Base Addr Size Type Attr Idx E Section Name Object
0x20000000 0x00000060 Zero RW 63 .bss c_w.l(libspace.o)
0x20000060 0x000007d0 Zero RW 2 HEAP startup_tm4c123.o
0x20000830 0x00007830 Zero RW 1 STACK startup_tm4c123.o
5-if RW is the size of RAM why it has 0 size even though I declared variables? and where does ER_ZI data located? they basically took bigger chunk than the available RAM as I explained above.
6- once someone explain the RAM size here, does the total RAM size here will include those functions nested in the main functions or even if there is a function calling 5 other functions does this RAM size include all the data could possible used statically in RAM? (not talking about dynamic allocation now) because as far I know when function is over it frees the space in RAM but how will this be illustrated in the .map file?
Please I need answers for all these doubts because I can't find then online. and thanks
