Placing a delay within any built-in function pertaining to the wireless radio will only halt operations on the Wi-Fi core or core0. Your main loop code wont be affected by a delay placed in core0. It will only halt wireless operations.

I ran into a similar issue and it took a while for me to put it together. I use global variables when passing info between core0 and core1.

• Wireless runs on core0 and
• Your main code runs on core1 (unless otherwise specified in the setup).

Delay (traditionally) has two functions that it performs:

1. Wait for a period
2. Yield processing to other threads through the yield() weak symbol.

By using a delay(0) the author thinks they are saying "I don't want to delay here, but if anything is using the yield() function it can run now."

However, that is not correct.

The code for delay() in the AVR core looks like this:

void delay(unsigned long ms) 
{
    uint32_t start = micros();

    while (ms > 0) {
        yield();
        while ( ms > 0 && (micros() - start) >= 1000) {
            ms--;
            start += 1000;
        }
    }   
}

You can see that, as well as delaying for a period, yield() is regularly called. However that only ever happens if ms is greater than 0. If you pass 0 as the delay length then the delay() function essentially does nothing at all.

Now it could be that an earlier version of the core had yield() always being called even with ms==0, but the current version doesn't. Maybe this is a hangup from an old coding style. But for the current core if you want to yield you must explicitly call yield() or delay for at least one millisecond.