Arduino MKR WiFi 1010 memory management

[semyuelshekh]

according to the official documentation of the Arduino microcontroller, the SRAM memory (which is allocated for the local variables) should be automatically released after calling any function. For example, I have a function memory_allocate_test2, which declares a large char array and this function is called in the loop(). I expect, that every time, after the function memory_allocate_test2 is executed, the SRAM memory that I allocated for the local variables within that function should be freed or released. However, it is not working like that. When I call that function in a loop() the microcontroller hangs and stops working because it runs out of the available SRAM memory. Let me provide an example code:

void setup() {
      //Initialize serial and wait for port to open:
      Serial.begin(9600);
      
      while (!Serial) {
        ; // wait for serial port to connect. Needed for native USB port only - development mode. It has to be removed when releasing to live!!!
      }
    }
    
    void loop() {
      delay(2000);
      memory_allocate_test2();
    }
    
    void memory_allocate_test2() {
      Serial.println("memory_allocate_test2 STARTING ");
      display_freeram();
      Serial.println("------------------------------------------------------------");
      Serial.println("Allocating the memory for the MKR: ");
      char* memory_usage_test = new char[2000];
      Serial.println("Allocated memory!");
      display_freeram();
      Serial.println("------------------------------------------------------------");
    }
    
    extern "C" char* sbrk(int incr);
    
    void display_freeram(){
      Serial.print(F("- SRAM left: "));
      Serial.println(freeRam());
    }
    
    int freeRam() {
      char top;
      return &top - reinterpret_cast<char*>(sbrk(0));
    }

why the microcontroller device and the firmware doesn't work as it states in the documentation? what I'm doing wrong? why the SRAM memory is not released each time after the memory_allocate_test2 function execution?

Managing Arduino Memory: Flash, SRAM, EEPROM! - Latest Open Tech From Seeed

when I execute that program, here is what happens:

memory_allocate_test2 STARTING

• SRAM left: 7163

---

Allocating the memory for the MKR:
Allocated memory!

• SRAM left: 5155

---

memory_allocate_test2 STARTING

• SRAM left: 5155

---

Allocating the memory for the MKR:
Allocated memory!

• SRAM left: 3147

---

memory_allocate_test2 STARTING

• SRAM left: 3147

---

Allocating the memory for the MKR:
Allocated memory!

• SRAM left: 1139

---

memory_allocate_test2 STARTING

• SRAM left: 1139

---

Allocating the memory for the MKR:
Allocated memory!

• SRAM left: -869

---

memory_allocate_test2 STARTING

• SRAM left: -869

---

Allocating the memory for the MKR:

at that point the microcontroller device just hangs and stops working. That's not what I expect!

[Delta_G]

@semyuelshekh

char* memory_usage_test = new char[2000];

Variables on the stack go away. You're creating something in the heap with new. You need to free that yourself.

Try with this function:

void memory_allocate_test2() {
      Serial.println("memory_allocate_test2 STARTING ");
      display_freeram();
      Serial.println("------------------------------------------------------------");
      Serial.println("Allocating the memory for the MKR: ");
      char memory_usage_test[2000] = "Hello World";
      Serial.println(memory_usage_test);  // print it so it isn't optimized away
      Serial.println("Allocated memory!");
      display_freeram();
      Serial.println("------------------------------------------------------------");
    }