MCG_Lite is used in many KL parts and is a less advanced clock generator
than the full MCG used in the K series. This change lets the MCG_Lite
and MCG share the same user facing API, with some configuration
differences.
Use RTC helper functions instead of libc functions.
This gives us y2038 safety by the extended epoch
and saves a good chunk of memory:
mktime():
text data bss dec hex filename
24756 232 2736 27724 6c4c testssperiph_rtc/bin/openlabs-kw41z-mini/tests_periph_rtc.elf
rtc_mktime():
text data bss dec hex filename
16348 132 2696 19176 4ae8 tests/periph_rtc/bin/openlabs-kw41z-mini/tests_periph_rtc.elf
On cppcheck 1.82 it throws a warning.
Since it costs cycles and does nothing the ++dummy is (void)dummy.
A warning suppression is added so the CI is happy.
This fixes the positive result when master write data is NACKed.
This false positive occurs when the write frame is finished but a data nack occurred.
The AF check should occur first.
Spinning for the correct time has the side effect that it may cause
infinite recursion if the callback function calls timer_set.
timer_set->callback->...->timer_set->callback->...->timer_set-> infinity
In theory, the drawback is that the callback for very short timeouts
(<2 lptmr ticks) may be delayed up to 2 lptmr ticks (61 µs)
In practice however, tests performed using tests/bench_timers shows that
this change only affects the accuracy of the timer target when timer_set
is called with a timeout of 0, which results in a delay of 30 µs.
By not forcing a fixed oversampling rate we can achieve better baud rate
accuracy than otherwise possible.
For example, when requesting 115200 with a module clock of 4 MHz,
picking an oversampling rate of 17 (instead of hardware
default 16) yields 117647 baud instead of 125000 baud as the best
matching rate. Better matching baud rate between receiver and
transmitter results in a lower probability of transmission errors.
Measurements show that the time from pin edge until return from
interrupt is reduced from 22 us to 6.1 us for KW41Z running at
41.94 MHz. The measurements used a no-op GPIO callback for testing and
were measured using an external logic analyzer.
This allows a board configuration to select which kind of averaging
should be applied to the pin instead of always using 32 sample average.
Very high impedance sources may need to disable hardware averaging in
order to give correct values, the on-chip temperature sensor is one such
signal source.
- Keep counter value between resets
- Let kinetis_mcg_init manage the RTC oscillator, to avoid disrupting
the core clock in certain configurations
- Remove some unnecessary macros for hardware abstraction; all Kinetis
CPUs which have an RTC only have a single RTC instance, and the ISRs
and hardware registers are named the same way in all Kinetis CPU
headers.
