ESP32 Forum

Hi,
It seems that there is an additional OS in the ROM (with APIs in ets_sys.h) and it is not the FreeRTOS.
Is there a document that describes the "Espressif Task Scheduler" principles ?

It's not an OS, it's a simple cooperative scheduler that stems from back in the ESP8266 days. While we do use some of the functions that are in that 'namespace' (as in, prefixed with ets_, like ets_printf) as baremetal functions for use in e.g. the bootloader, the scheduler itself is 'dead code' which we leave in as it's tiny anyway (200'ish lines of C). It's not public, sorry, but it wouldn't be hard to build an equivalent yourself.