I'm looking at porting your arduino-like lib and your LwIP lib for use with Teensy 3.5/3.6/4.1. I have an lwip implmentation that uses callbacks and polling with the Teensy. I haven't run any tests with your libs yet, so my question is based on code inspection. As I understand your non-RTOS implementation, there seems to be a potential conflict (race condition) with the timer-based (1 ms) calls to stm32_eth_scheduler() and the calls to the scheduler embedded in DHCP and UDP modules. It would seem a timer-based call to the scheduler could interrupt a scheduler invocation from DHCP or UDP. Thanks for any enlightenment.