Zephyr and the Memory Footprint

Do you want to use Zephyr RTOS on a Microcontroller with only a few bytes of Flash? Let's try it!

On the Optimizing for Footprint doc site you will find some hints how to reduce the memory footprint. Ok let's do it. I compiled the following application by using this configs:

main.c: void main (void) { uint32_t i = 0; // run the loop for ever while (true) { i++; } }

prj.conf: # disable all peripherals CONFIG_GPIO=n CONFIG_SERIAL=n CONFIG_SPI=n CONFIG_I2C=n # disable the boot banner CONFIG_BOOT_BANNER=n #disable all debug and log messages CONFIG_DEBUG=n

With this application and settings I could reduce the kernel to 6872 bytes:

west build -p auto -b <board name>

Memory region         Used Size  Region Size  %age Used
           FLASH:        6872 B        16 KB     41.94%
            SRAM:        1232 B         2 KB     60.16%
        IDT_LIST:          56 B         2 KB      2.73%

Ok, this is just the kernel to have an idea how much flash it needs. You can analyze the memory usage from the rom/ram-report (for more details have a look at the Zephyr Optimization Tools).

But how much does a small hello world application need, for example?