ArduinoCore-renesas

They've done a good job of hiding the RTOS from you and making most sketches run fine without porting, but you're still running as a task under the RTOS, yielding between loop() calls[1]. This leads to mysterious timing issues if you aren't aware of it[2] It doesn't appear that the Arduino core for the Renesas chip is using the RTOS, at least by default -- its main loop is literally doing while (1) { loop(); }, similar to how the AVR core works. [3, 4] 1. https://github.com/espressif/arduino-esp32/blob/72c41d09538663ebef80d29eb986cd5bc3… 2. https://www.reddit.com/r/esp32/comments/t9aqr6/what_on_earth_is_my_esp32_doing_bet… 3. https://github.com/arduino/ArduinoCore-renesas/blob/149f78b6490ccbafeb420f68919c38… 4. https://github.com/arduino/ArduinoCore-avr/b

it's all open source, you can see part of it here https://github.com/arduino/ArduinoCore-renesas you can use GCC with https://github.com/renesas/fsp if you want to go very low level.