This is a temporary fix for Issue #17060. It allows to disable
auto inclusion of `ztimer_periph_rtt` in cases where another
module or application requires direct access.
Limitations:
- as ifeq are involved order of inclusion matters, therefore
these modules should be included early in the build at application
level and not in modules `Makefile.dep`
- this does not disallow direct inclusions of `ztimer_periph_rtt`,
since this only disables auto inclusion of these modules
This is a temporary solution since this is already possible with
Kconfig, but not in make.
wire up ZTIMER_SEC to the existing RTC backend, or RTT backend, or periph_timer
backend (in this order of preference).
Update sys/ztimer/auto_init.c
Co-authored-by: Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
`ztimer_init_extend()` should only be defined when module `ztimer_extend` is
used, as otherwise the `struct` member `clock->max_value` is not available.
ztimer_clock are meant to be chained. At the end of the chaine
there is always a timer device object (periph_rtt/rtc/timer).
Since ZTIMER_MSEC and ZTIMER_USEC can be the scaled/shifted with
respect to the base periph_rtt/rtc/timer it makes sense to chain
other ZTIMER_XXX on top of the base rtc/timer/rtt in order to avoid
chained convertions.
