FAQs
cancel
Turn on suggestions
Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for 
Search instead for 
Did you mean: 

Linker Script , optimisation

gfoujanet
Associate II

‎2014-02-28 06:05 AM

Posted on February 28, 2014 at 15:05

Hello,

I would like to be sure I understand the linker script that I am using. My main question is : the code is it copy to RAM before to be executed? I think It's not the case, because the code is .text section, that is just copy to FLASH with >FLASH. (the linker script is a copy from ST source + some modifications ) 


/*

*****************************************************************************

**

** File : stm32_mdp.ld

**

** Abstract : Linker script for stm32l1xx_mdp Device 

**

** Set heap size, stack size and stack location according

** to application requirements.

**

** Set memory bank area and size if external memory is used.

**

** Target : STMicroelectronics STM32

**

**** Distribution: The file is distributed �as is,� without any warranty

** of any kind.

**

** (c)Copyright Atollic AB.

** You may use this file as-is or modify it according to the needs of your

** project. Distribution of this file (unmodified or modified) is not

** permitted. Atollic AB permit registered Atollic TrueSTUDIO(R) users the

** rights to distribute the assembled, compiled & linked contents of this

** file as part of an application binary file, provided that it is built

** using the Atollic TrueSTUDIO(R) toolchain.

**

*****************************************************************************

*/


/* Entry Point */

ENTRY(Reset_Handler)


/* Highest address of the user mode stack */

_estack = 0x20008000; /* end of 32K RAM */

__ICFEDIT_region_RAM_end__ = _estack;


/* Generate a link error if heap and stack don't fit into RAM */

_Min_Heap_Size = 0; /* required amount of heap */

_Min_Stack_Size = 0x200; /* required amount of stack */


/* Specify the memory areas */

MEMORY

{

FLASH (rx) : ORIGIN = 0x00000000, LENGTH = 256K /*- 0x3000*/

RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 32K

MEMORY_B1 (rx) : ORIGIN = 0x60000000, LENGTH = 0K

}


/* Define output sections */

SECTIONS

{

/* The startup code goes first into FLASH */

.isr_vector :

{

. = ALIGN(4);

KEEP(*(.isr_vector)) /* Startup code */

. = ALIGN(4);

} >FLASH


/* The version number is placed before the beginning of code */

.nb_version :

{

. = ALIGN(4);

KEEP(*(.nb_version)) /* KEEP the variable even if not referenced */

. = ALIGN(4);

} >FLASH


/* The program code and other data goes into FLASH */

.text :

{

. = ALIGN(4);

_stext = .; /* define a global symbols at start of code */


*(.text) /* .text sections (code) */

*(.text*) /* .text* sections (code) */

*(.rodata) /* .rodata sections (constants, strings, etc.) */

*(.rodata*) /* .rodata* sections (constants, strings, etc.) */

*(.glue_7) /* glue arm to thumb code */

*(.glue_7t) /* glue thumb to arm code */

*(.eh_frame)


KEEP (*(.init))

KEEP (*(.fini))


. = ALIGN(4);

_etext = .; /* define a global symbols at end of code */

} >FLASH


__checksum = _stext;

__end_of_code = _etext;


.ARM.extab : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >FLASH

.ARM : {

__exidx_start = .;

*(.ARM.exidx*)

__exidx_end = .;

} >FLASH


.preinit_array :

{

PROVIDE_HIDDEN (__preinit_array_start = .);

KEEP (*(.preinit_array*))

PROVIDE_HIDDEN (__preinit_array_end = .);

} >FLASH

.init_array :

{

PROVIDE_HIDDEN (__init_array_start = .);

KEEP (*(SORT(.init_array.*)))

KEEP (*(.init_array*))

PROVIDE_HIDDEN (__init_array_end = .);

} >FLASH

.fini_array :

{

PROVIDE_HIDDEN (__fini_array_start = .);

KEEP (*(.fini_array*))

KEEP (*(SORT(.fini_array.*)))

PROVIDE_HIDDEN (__fini_array_end = .);

} >FLASH


/* used by the startup to initialize data */

_sidata = .;


/* Initialized data sections goes into RAM, load LMA copy after code */

.data : AT ( _sidata )

{

. = ALIGN(4);

_sdata = .; /* create a global symbol at data start */

*(.data) /* .data sections */

*(.data*) /* .data* sections */


. = ALIGN(4);

_edata = .; /* define a global symbol at data end */

} >RAM

__ICFEDIT_region_RAM_end__ = _edata; /* used to check the RAM used */


/* Uninitialized data section */

. = ALIGN(4);

.bss :

{

/* This is used by the startup in order to initialize the .bss secion */

_sbss = .; /* define a global symbol at bss start */

__bss_start__ = _sbss;

*(.bss)

*(.bss*)

*(COMMON)


. = ALIGN(4);

_ebss = .; /* define a global symbol at bss end */

__bss_end__ = _ebss;

} >RAM


PROVIDE ( end = _ebss );

PROVIDE ( _end = _ebss );


/* User_heap_stack section, used to check that there is enough RAM left */

._user_heap_stack :

{

. = ALIGN(4);

. = . + _Min_Heap_Size;

. = . + _Min_Stack_Size;

. = ALIGN(4);

} >RAM


/* MEMORY_bank1 section, code must be located here explicitly */

/* Example: extern int foo(void) __attribute__ ((section (''.mb1text''))); */

.memory_b1_text :

{

*(.mb1text) /* .mb1text sections (code) */

*(.mb1text*) /* .mb1text* sections (code) */

*(.mb1rodata) /* read-only data (constants) */

*(.mb1rodata*)

} >MEMORY_B1


/* Remove information from the standard libraries */

/DISCARD/ :

{

libc.a ( * )

libm.a ( * )

libgcc.a ( * )

}


.ARM.attributes 0 : { *(.ARM.attributes) }

}

And the gcc startup code just copies the .data section to RAM, but does'nt copy the .text to RAM.(line 16) 


.section .text.Reset_Handler

.weak Reset_Handler

.type Reset_Handler, %function

Reset_Handler:


/* Copy the data segment initializers from flash to SRAM */ 

movs r1, #0

b LoopCopyDataInit


CopyDataInit:

ldr r3, =_sidata

ldr r3, [r3, r1]

str r3, [r0, r1]

adds r1, r1, #4


LoopCopyDataInit:

ldr r0, =_sdata

ldr r3, =_edata

adds r2, r0, r1

cmp r2, r3

bcc CopyDataInit

ldr r2, =_sbss

b LoopFillZerobss

/* Zero fill the bss segment. */ 

FillZerobss:

movs r3, #0

str r3, [r2], #4


LoopFillZerobss:

ldr r3, = _ebss

cmp r2, r3

bcc FillZerobss

/* Call the application's entry point.*/

bl main

bx lr

.size Reset_Handler, .-Reset_Handler

I would like to confirm with you that my code is not running from RAM but it's running from Flash. If it's the case, I can optimize the speed of my application! Thank you very much for your help, #linker-script-stm32
0 Kudos
3 REPLIES 3
chen
Associate II

‎2014-02-28 06:19 AM

Posted on February 28, 2014 at 15:19

Hi

''I would like to confirm with you that my code is not running from RAM but it's running from Flash.''

That looks correct to me, the linker is putting the program in Flash.

0 Kudos
gfoujanet
Associate II

‎2014-03-03 05:19 AM

Posted on March 03, 2014 at 14:19

Thank you for your answer.

The code size is too big to be in RAM. Can i just put a part of the code to RAM, and the other part is in FLASH ?

I hope that the execution from RAM is quicker than from FLASH...

Thanks a lot

0 Kudos
chen
Associate II

‎2014-03-03 06:51 AM

Posted on March 03, 2014 at 15:51

Hi

''Can i just put a part of the code to RAM, and the other part is in FLASH ?''

Yes.

It is a little bit more complicated than the variables in RAM.

The linker must locate the code in RAM but also store it in Flash.

Some code must copy the code from Flash into RAM before it is called.

''I hope that the execution from RAM is quicker than from FLASH...''

It depends.

Some STM32 have Flash acclerator and the Cache, these can make the Flash just as fast as the RAM.

0 Kudos
Top