Thanks for the link, @lbernstone. From there I can see:
Darn.

I want to use a timer (`esp_timer_create`) with ISR dispatch. The docs say this requires:


esp_timer_create_args_t timer_config;
...
timer_config.dispatch_method = ESP_TIMER_ISR;


Where `ESP_TIMER_ISR` is only defined if `CONFIG_ESP_TIMER_SUPPORTS_ISR_DISPATCH_METHOD` is also defined. In my code ...

I'm moving an Arduino-esq project from ESP8266 to ESP32 and naively hoped it would be as simple as changing the board type and re-compiling. Not so :(

In particular, I was making use of `Schedule.h` (https://github.com/esp8266/Arduino/blob/master/cores/esp8266/Schedule.h), but this is not present ...