How is memory allocated?

[butaikis]

Hi @bblanchon. I have ESP32-WROVER-IE (FLASH 8MB, PSRAM 8MB). I tested different amounts of memory allocation for JSON

DynamicJsonDocument testjs{7000000}; or DynamicJsonDocument testjs{70000000};

In all cases, the test js.capacity() function returned the correct number of bytes. But I don't understand how, because I don't have that much RAM.

Code:

  OUTPUT_JSON["buf_testjs"] = testjs.capacity();
  OUTPUT_JSON["psram_size_all"] = esp_spiram_get_size();
  OUTPUT_JSON["psram_size"] = ESP.getPsramSize();
  OUTPUT_JSON["psram_free"] = ESP.getFreePsram();
  OUTPUT_JSON["free_heap"]  = ESP.getFreeHeap();
  OUTPUT_JSON["free_heap2"]  = heap_caps_get_free_size(MALLOC_CAP_8BIT);
  OUTPUT_JSON["psram_himem_size"]  = esp_himem_get_phys_size();

Result:

  "buf_testjs": 70000000,
  "psram_size_all": 8388608,
  "psram_size": 3913347,
  "psram_free": 3791467,
  "free_heap": 55187,
  "free_heap2": 3809434,
  "psram_himem_size": 4456448