Is it possible to use PSRAM for embassy task-arena / static data / ...?

[yanshay]

I'm developing on esp32s3 and have lots of PSRAM available but still short on memory.
Can embassy task-arena be located in PSRAM? or maybe it already is?
Is it possible to place all static data in PSRAM?
Can the stack be in PSRAM? (that's probably impossible but checking in case it is)
Any other options to relocate memory usage that isn't alloc to PSRAM?

[bjoernQ]

I think the task-arena is always allocated on the stack and the stack shouldn't live in PSRAM

We currently don't support static data in PSRAM for a couple of reasons.

The linker scripts don't create a segment for PSRAM IIRC (since the PSRAM size is detected at runtime this would be a problem) so you can also not have uninitialzed data there - basically, you need alloc for this

[bugadani]

Just to correct you a bit, the task arena is a static in embassy-executor, outside of our control:

https://github.com/embassy-rs/embassy/blob/46f91151693c68c074293ddc4daf0c94058f9587/embassy-executor/src/lib.rs#L117

[bjoernQ]

ah thanks - never thought about that 👍

[yanshay]

I'm actually using embassy with nightly now, so not to have to modify the arena all the time as my code grows. I see it's using some kind of allocating mechanism.

But seems like it may be possible to extend embassy to use an external allocator there in a single place and make it support PSRAM.
I'll try to look into it.

Could using PSRAM for embassy cause any issues with certain activities that can't take place in PSRAM? (e.g. I think esp-wifi is using embassy behind the scenes or at least the tasks run under embassy)

[bugadani]

But seems like it may be possible to extend embassy to use an external allocator there in a single place and make it support PSRAM.
I'll try to look into it.

You can see a similar solution at https://github.com/card-io-ecg/card-io-fw/tree/main/embassy-alloc-taskpool