Compiler/TMS570LC4357: .sysmem creation for Heap without memory.c

Someswararao malla

Intellectual 450 points

Part Number: TMS570LC4357

Tool/software: TI C/C++ Compiler

Hi Ti Experts,

This is with respect to previous query provided below

https://e2e.ti.com/support/microcontrollers/hercules/f/312/p/805194/2994497#2994497

Heap start and end addresses i am getting properly, my understanding was wrong.
I have another question with respect to this, i am using memory.c file from the ti.
If i exclude memory.c file from my build, i could see the .sysmem section not created in map file.
Heap start and end addresses are showing save value.
when i was looking at the memory.c file, i observed the below part of code from memory.c is creating the .sysmem.
Can you please explain without these changes why .sysmem is not created, unlike other sections, and what _sys_memory will hold.

typedef struct pack
{
size_t packet_size; /* number of bytes */
struct pack *size_ptr; /* next elem in free list */
} PACKET;
#pragma DATA_SECTION(_sys_memory, ".sysmem")
PACKET _sys_memory[1];

Regards,
Somesh

over 6 years ago

0 George Mock over 6 years ago

TI__Guru**** 252340 points

Here is how it usually works. The main application calls malloc, or a similar function which dynamically allocates memory from the heap. This causes the linker to search the RTS library. It finds the file memory.obj (built from memory.c) provides a definition of the function malloc. So the linker brings in memory.obj from the RTS library. The file memory.obj defines the section .sysmem and the symbol _sys_memory. If the main application does not call malloc, then there is no definition of the section .sysmem or the symbol _sys_memory.

The symbols HEAP_START etc. are not created by default. Your linker command file must create them.

Thanks and regards,

-George

0 Someswararao malla over 6 years ago in reply to George Mock

Intellectual 450 points

Hi George,

Though i have added malloc calls in my code if i comment out the below line, .sysmem is not created.

PACKET _sys_memory[1];

Regards,

Somesh

0 George Mock over 6 years ago in reply to Someswararao malla

TI__Guru**** 252340 points

Yes, that is true. But I fail to see why it is meaningful. If you make any changes to the RTS source code, then it can cause problems like this.

Thanks and regards,

-George

0 Someswararao malla over 6 years ago in reply to George Mock

Intellectual 450 points

Hi George,

We are not using RTS library, and want to directly export the heap start and end addresses from the linker command.

Can you please help on this.

Regards,

Somesh

0 George Mock over 6 years ago in reply to Someswararao malla

TI__Guru**** 252340 points

Please tell me about the overarching problem you want to solve. Just for now, please forget everything you know about linker command files, symbols, and so on. Describe, as simply as you can, what you want to do. I need that context. And I may be able to suggest a better way to do it.

Thanks and regards,

-George

0 sreenivasan m over 6 years ago in reply to George Mock

Genius 3705 points

Hi George,

As per spnu151t.pdf document,

--heap_size=size [-]-heap Sets heap size (for the dynamic memory allocation in C) to size bytes and defines a
global symbol that specifies the heap size. Default = 2K bytes.

Can you please provide us the global name as mentioned above, so that we can refer that in our code?

0 George Mock over 6 years ago in reply to sreenivasan m

TI__Guru**** 252340 points

sreenivasan m said:
Can you please provide us the global name as mentioned above

__SYSMEM_SIZE

Thanks and regards,

-George

0 sreenivasan m over 6 years ago in reply to George Mock

Genius 3705 points

Thanks George. Can you please share an example on how to use these symbol?

0 George Mock over 6 years ago in reply to sreenivasan m

TI__Guru**** 252340 points

Please search the ARM assembly language tools manual for the sub-chapter titled Using Linker Symbols in C/C++ Applications.

Thanks and regards,

-George

Arm-based microcontrollers

Arm-based microcontrollers forum

Compiler/TMS570LC4357: .sysmem creation for Heap without memory.c