Variable doesn't update between cores

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Don't use bitbang logic like that; the ESP32 is not designed for that. On one hand, it's a pretty complex beast needing RTOS and realtime interrupts for e.g. WiFi to work, making delays like this unreliable. On the other hand, you have a gazillion of peripherals (RMT, for example) that you can use to offload the task from the CPU.