power_down_unused_ram() compatibility with malloc()/free()?

RE: power_down_unused_ram() compatibility with malloc()/free()?

Håkon Alseth — Fri, 15 Mar 2024 08:30:12 GMT

Hi Steve,

I'm happy to help out.

These lower layer stuff can be a bit tricky. What I can say is that you will definitely notice quite quickly if parts of your used RAM is powered off :-)

Let us know if you run into any issues or have questions.

Hope you have a great weekend!

Kind regards,

Håkon

RE: power_down_unused_ram() compatibility with malloc()/free()?

SteveKranz — Thu, 14 Mar 2024 20:32:16 GMT

Hi Håkon,

Oh, ok, very cool. Thank you for the timely response. We appreciate it...

:-)

Steve

RE: power_down_unused_ram() compatibility with malloc()/free()?

Håkon Alseth — Thu, 14 Mar 2024 11:32:39 GMT

Hi,

[quote user="SteveKranz"]I still am left wondering if it is safe for applications and libraries to use malloc/free if the system has been placed in the power_down_unused_ram() mode and the CONFIG_RAM_POWER_ADJUST_ON_HEAP_RESIZE is not set. [/quote]

The .heap will be placed within the limits, ie. _start and _end symbol. Therefore it shall not be deemed "unused".

Kind regards,

Håkon

RE: power_down_unused_ram() compatibility with malloc()/free()?

SteveKranz — Thu, 14 Mar 2024 00:23:13 GMT

Hi Håkon,

Hmmmm? I still am left wondering if it is safe for applications and libraries to use malloc/free if the system has been placed in the power_down_unused_ram() mode and the CONFIG_RAM_POWER_ADJUST_ON_HEAP_RESIZE is not set. Maybe I missed it in your reply, but I still can't say for sure. Can you confirm?

Thanks in advance!

Steve.

RE: power_down_unused_ram() compatibility with malloc()/free()?

Håkon Alseth — Wed, 13 Mar 2024 14:43:38 GMT

Hi,

[quote user=""]CONFIG_RAM_POWER_ADJUST_ON_HEAP_RESIZE

My concern is that our system does not set this and we are wondering if we should. We were planning to use the malloc()/free() calls, and we have no idea if the underlying matter/thread layers also use malloc()/free(). Are we running the risk that something will break if malloc()/free() are used in a system that has been placed in the power_down_unused_ram(). Maybe power_down_unused_ram() isn’t a set-it-and-forget-it function? I notice that both of the following functions exist:

power_down_unused_ram()
power_up_unused_ram()

Another way to ask my question is: Under what conditions would we need to call power_up_unused_ram()?[/quote]

in matter projects, the heap size is set up by the matter stack itself, more specifically in this module:

https://github.com/nrfconnect/sdk-connectedhomeip/blob/v2.6.0-rc2/src/platform/Zephyr/SysHeapMalloc.cpp#L41

If you do not enable CONFIG_RAM_POWER_ADJUST_ON_HEAP_RESIZE, it will adjust the RAM blocks based on the RAM start and RAM end symbols:

https://github.com/nrfconnect/sdk-nrf/blob/v2.5.2/lib/ram_pwrdn/ram_pwrdn.c#L195-L203

[quote user=""]Another way to ask my question is: Under what conditions would we need to call power_up_unused_ram()?[/quote]

Provided that you never use the RAM, you shouldn't need to power up the segments. This is provided as a dynamic feature, in cases where you need to use previously unused segments of RAM.

Kind regards,

Håkon