How to use PSRAM on ESP32-S3 NON VOLATILE to CPU reset in IDF

[MichaelS]

Hi
I have a project using ESP32-S3 modules and IDF.
I want to use the PSRAM as memory which is non volatile across a CPU reset. I understand it is NOT non volatile over a power loss.
I want to be able to store data records in a FIFO type structure.
What is the best strategy for doing this?

A VFS RAM disk with non volatile across a reset would also be a good solution, but does not seem the exist?

I tried enabling PSRAM and using heap_caps_malloc(..., MALLOC_CAP_SPIRAM) and found that while I could access the RAM fine, I realized the memory contents would be lost after a reset by the allocation and creation of a variables with a custom allocator. Is there any way of avoiding this and also ensuring the allocation is repeatable across a reset?

I also found when the PSRAM was enabled (in Menu config) but not even used (no calls to heap_caps_malloc(..., MALLOC_CAP_SPIRAM)), my application went a bit weird. OTA updates using HTTPS slowed down and eventually failed. My OTTA HTTPS code was taken from IDF example "advanced_https_ota". Is there something I could have done wrong or could set to fix this? I can reproduce the problem just by enabling PSRAM (in menu-config) and fix it by disabling it again.

So I thought I would have to write my own interface where I can control the memory addressing and ensure no initialization or clearing happens on CPU rest.
I looked at the data sheet of the ESP32­S3­WROOM­1 module to find out what GPIO are used for the PSRAM SPI bus and am now very confused.
Section 5 Module Schematics does not show any PSRAM chip? Is it built into the ESP32 SOC?
Also for the SPI Flash it shows standard SPI when I thought it would be octal-SPI or quad-SPI? Is this not the main program Flash, and is it also built into the ESP32 SOC

[aliarifat794]

You can use the esp_himem API (available for PSRAM access) to allocate specific memory blocks. These allocations can be fixed at known addresses, allowing you to manage them directly.

Code: Select all

esp_himem_handle_t handle;
esp_himem_reserved_handle_t reserved;
void* psram_fifo = NULL;

esp_himem_alloc(PSRAM_FIFO_SIZE, &handle);
esp_himem_alloc_map(handle, &reserved, PSRAM_FIFO_SIZE, 0, &psram_fifo);
// Use `psram_fifo` as the FIFO base address.

[ESP_Sprite]

You can use the esp_himem API (available for PSRAM access) to allocate specific memory blocks.

No, you cannot. First of all, the himem api is not intended for that. Secondly, it only works on the original ESP32.

For something that does work, you probably want EXT_RAM_NOINIT_ATTR as described in the docs.