Apache NuttX is a mature, real-time embedded operating system (RTOS) https://nuttx.apache.org/

embeddedmcumicrocontrollernuttxreal-timertos

Gregory Nutt c09622b0f6 Merged in wail007/arch (pull request #33) ... Added a lower-half timer driver for stm32 which is compatible with the upper-half driver located at /drivers/timers/timer.c		2015-11-17 16:26:20 -06:00
arch	Added a lower-half timer driver for stm32 which is compatible with the upper-half driver located at /drivers/timers/timer.c	2015-11-17 16:57:02 -05:00