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Malloc returns NULL

Setup

Keil: uVision 5.17.0.0
ARM: LPC1768
A standard project with some UARTS and I2C
"Use memory Layout form target" is checked (using the standard scatter file)
"Use MicroLIB" is not checked

from startup_LPC17xx.s
Heap_Size EQU 0x00002000

AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit

Problem
Any call to malloc returns NULL, that is, the system can not allocate memory.

Why does not the mallco work, is my only options to
1) Use microLIB
2) Implement _init_alloc() and __rt_heap_extend() on my own

Regards Stefan

Parents

0 Stefan Olsson over 8 years ago in reply to Robert McNamara

It works now as expected, it was all related to one of all of the added lines at the top of startup_LPC..

                EXPORT  __initial_sp
                EXPORT  __heap_base
                EXPORT  __heap_limit

If any of them, even if the program only have "EXPORT __initial_sp" (and not the other two) the heap dont get initalized. If none of them are exported then the runtime library will call __user_initial_stackheap as expected.

It is neccessary to export a new/seperate variabel if the stack top is going to be used
somewhere else, like this

                EXPORT  __initial_stack_top


Stack_Size      EQU     0x00000800

                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp
__initial_stack_top

One interesting observation was that if the program had

                EXPORT  __initial_sp
                EXPORT  __heap_base
                EXPORT  __heap_limit

The map file will contain
__rtentry4.o(.ARM.Collect$$rtentry$$00000004) refers to sys_stackheap_outer.o(.text) for __user_setup_stackheap
sys_stackheap_outer.o(.text) refers to startup_lpc17xx.o(.text) for __user_initial_stackheap

But they was never called

Conclusive:
Dont export any of __initial_sp, __heap_base or __heap_limit form the startup_XXXX.s

Reply

0 Stefan Olsson over 8 years ago in reply to Robert McNamara

It works now as expected, it was all related to one of all of the added lines at the top of startup_LPC..

                EXPORT  __initial_sp
                EXPORT  __heap_base
                EXPORT  __heap_limit

It is neccessary to export a new/seperate variabel if the stack top is going to be used
somewhere else, like this

                EXPORT  __initial_stack_top


Stack_Size      EQU     0x00000800

                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp
__initial_stack_top

One interesting observation was that if the program had

                EXPORT  __initial_sp
                EXPORT  __heap_base
                EXPORT  __heap_limit

The map file will contain
__rtentry4.o(.ARM.Collect$$rtentry$$00000004) refers to sys_stackheap_outer.o(.text) for __user_setup_stackheap
sys_stackheap_outer.o(.text) refers to startup_lpc17xx.o(.text) for __user_initial_stackheap

But they was never called

Conclusive:
Dont export any of __initial_sp, __heap_base or __heap_limit form the startup_XXXX.s

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