static_malloc

This library is just an Arduino wrapper around Andrey Rys static memory allocator library smalloc (https://github.com/electrorys/smalloc). The full credit for the very useful code goes to Andrey of course. Here his man-page of smalloc

For the convenience of Arduino users I sorted the original files into the folders required by the Arduino library specification and added a few usage examples. I also added a header handling the extern "C" wrapper which is required for the usual Arduino ino/cpp projects.

The main purpose of this library is to enable dynamic memory allocation on one or more predefined static buffers. This buffer can be placed wherever you want. Thus, the library can easily be used to dynamically access external memory chips like the optional 8MB PSRAM on the Teensy 4.1.

Here a quick example showing the usage:

#include "static_malloc.h"

constexpr size_t myHeapSize = 1024 * 100;
EXTMEM uint8_t myHeap[myHeapSize]; // 100kB memory pool on the external ram chip

//----------------------

float* floatArray;
uint32_t* u1;
char* text;

void setup()
{
    sm_set_default_pool(myHeap, myHeapSize, false, nullptr); // use a memory pool on the external ram

    u1 = (uint32_t*)sm_malloc(sizeof(uint32_t));        // 1 uint32_t
    floatArray = (float*)sm_malloc(10 * sizeof(float)); // Array of 10 floats
    text = (char*)sm_malloc(100);                       // c-string 100 bytes

    *u1 = 100;
    for (int i = 0; i < 10; i++) { floatArray[i] = i * M_PI; }
    text = strcpy(text, "Hello World");

    while (!Serial) {}
    Serial.println(text);
    Serial.println(*u1);
    Serial.println(floatArray[4]);
}

void loop()
{
}

Off course, smalloc also provides sm_free and sm_calloc. Additionally, it can be used to handle more than one memory pool in parallel and provides an "out of memory" callback.

See the examples folder in the sources for more examples.

Here a quick video showing how sm_malloc allocs/frees memory. The Teensy code implements a 54000 byte static heap and smalloc randomly allocates and frees memory chunks on the heap. Each bar corresponds to one of the chunks. You find the corresponding firmware and (Win10) software in the extras folder.