Memory allocation limitations on the nRF52840?

RE: Memory allocation limitations on the nRF52840?

ray — Sun, 14 Mar 2021 08:51:21 GMT

I have a same problem.

I would like to allocate a buffer of 128KB.

it is not work well, eventhrough I changed heap size in the project setting.

I need more information.

how to use malloc function for make 128KB buffer.

I am using nrf52840, segger embedded studio V5.32a

RE: Memory allocation limitations on the nRF52840?

Nicholas Lee — Mon, 13 Aug 2018 12:55:08 GMT

Hi,

Thanks.

The XXLARGE block is defined in the sdk_config.h file as 3444 bytes, which is a strange and arbitrary number. I had assumed the smaller blocks would be fractions of that.

RE: Memory allocation limitations on the nRF52840?

Einar Thorsrud — Mon, 13 Aug 2018 08:09:28 GMT

Hi,

I agree that it would make sense to let any unused memory be part of the heap. You can achieve it by editing the section placement file (flash_placement.xml in the SDK projects). Replace the existing line that sets the heap (name=".heap") with the following line:

    <ProgramSection alignment="4" size="((__RAM_segment_end__ - __STACKSIZE__) - __heap_load_start__)" load="No" name=".heap" />

The nrf_malloc function is part of the Memory Manager library, which is more complex than the standard malloc function. The fixed size blocks are used to reduce memory fragmentation. The buffer sizes are configurable in the projects sdk_config.h (e.g. MEMORY_MANAGER_XXSMALL_BLOCK_SIZE). Where do you see that the buffer size increments are based on fractions of 3444?

RE: Memory allocation limitations on the nRF52840?

Nicholas Lee — Fri, 10 Aug 2018 13:12:51 GMT

Thank you.
Yes, changing that Heap Size value to 128KB now allows me to allocate sensibly sized arrays.

I don't understand why this Heap Size value is set in this obscure settings dialog as an arbitrary and tiny default value, instead of being automatically sized to be whatever the free memory for the chip is.

Also, can you shed any light on the nrf_malloc function? Is there any advantage to using that over malloc?
Why are the nrf_malloc buffer size increments based on fractions of 3444 instead of some power-of-2 number of bytes. Does this perhaps relate to some common application for this function?

RE: Memory allocation limitations on the nRF52840?

Einar Thorsrud — Fri, 10 Aug 2018 07:44:57 GMT

Hi,

You can set the heap (and stack) size under "Runtime Memory Area" in the project settings:

The longer story is that what you select above is put in the __HEAPSIZE__ and __STACKSIZE__ variable, which are used in the section-placement file. In the SDK examples this is called flash_placement.xml and is in the same directory as the project files for all SDK examples. Relevant snippet:

    <ProgramSection alignment="4" size="__HEAPSIZE__" load="No" name=".heap" />
    <ProgramSection alignment="8" size="__STACKSIZE__" load="No" place_from_segment_end="Yes" name=".stack"  address_symbol="__StackLimit"

RE: Memory allocation limitations on the nRF52840?

Olaf — Fri, 10 Aug 2018 06:28:59 GMT

Hi did you set the heap size correctly? https://devzone.nordicsemi.com/f/nordic-q-a/36578/memory-management-heap BR Olaf