Where are memory allocations for esp-mbedtls come from?

[yanshay]

I added some code using esp-mbedtls to an app I'm working on, and it now fails on Error -32512/-0x7f00 which I understand is 0x7F00 SSL - Memory allocation failed ?

I'm using PSRAM for memory as well.

Where does esp-mbedtls take memory from? Is it using PSRAM if available through alloc? Or is it limited to using the standard RAM which is more limited (and embassy seems to take a lot of space there)?

[AnthonyGrondin]

Currently is uses the calloc() / free() implementation provided by esp-wifi, which are wrappers over esp-alloc by default. We should refactor to use the default Rust allocator to be more platform agnostic.

[yanshay]

afaik (from @bjoernQ) esp-alloc is capable of setting requirement type of memory to use, whether it has to be RAM or can be PSRAM. I think normally esp-wifi, for its own allocation, must use RAM. In the case of esp-mbedtls, when going through esp-wifi, will it require RAM or will allow the use PSRAM?

Even if currently it's using only RAM, could it technically use PSRAM or has the same technical constraints of esp-wifi that require RAM?

[bjoernQ]

Yes esp-alloc supports allocating from specified memory types via a custom alloc function. A generic global allocator doesn't support that.

Some peripherals can only do DMA on internal RAM and for other peripherals there are some alignment requirements when using PSRAM. When not using DMA it shouldn't be a problem to use PSRAM (it's just slower than internal RAM)

[yanshay]

So if esp-mbedtls goes through esp-wifi which I recall does use DMA so use the internal RAM for its own usage, does it mean esp-mbedtls use the internal RAM as well?

And does the esp-mbedtls with all its hw accelerations use DMA?

As you can figure out I'm struggling with memory space 😄

[bjoernQ]

As long as esp-mbedtls is using esp-wifi's alloc it's allocating from internal RAM

I think the used crypto accelerators don't use DMA