RIOT/sys/xtimer/Makefile.dep

DEFAULT_MODULE += auto_init_xtimer
# In whatever combination of backends periph_timer will be required
# - xtimer (only) -> periph_timer
# - xtimer_on_ztimer -> ztimer_usec -> ztimer_periph_timer -> periph_timer
# - ztimer_xtimer_compat -> ztimer_usec -> ztimer_periph_timer -> periph_timer
# But requesting it here avoid an ifeq dependency that would be subject to
# dependency inclusion order issues
FEATURES_REQUIRED += periph_timer

ifeq (,$(filter xtimer_no_ztimer_default,$(USEMODULE)))
  ifeq (,$(filter xtimer_on_ztimer,$(USEMODULE)))
    USEMODULE += ztimer_xtimer_compat
  endif
else
  ifneq (,$(filter ztimer,$(USEMODULE)))
    ifeq (,$(filter xtimer_on_ztimer,$(USEMODULE)))
      USEMODULE += ztimer_xtimer_compat
    endif
  endif
endif

ifneq (,$(filter ztimer_xtimer_compat,$(USEMODULE)))
  DISABLE_MODULE += auto_init_xtimer
  USEMODULE += div
endif

# make xtimer use ztimer_usec as low level timer
ifneq (,$(filter xtimer_on_ztimer,$(USEMODULE)))
  USEMODULE += ztimer_usec
endif