Prior to this commit, the ADC calibration code was never executing because
ADVREGEN bit was set making the CR register always non-zero.
This commit changes the logic so that ADC calibration is always run when
the ADC is disabled and an ADC channel is initialised. It also uses the LL
API functions to do the calibration, to make sure it is done correctly on
each MCU variant.
Signed-off-by: Damien George <damien@micropython.org>
STM32F0 has PCLK=48MHz and maximum ADC clock is 14MHz so use PCLK/4=12MHz
to stay within spec of the ADC peripheral. In pyb.ADC set common sampling
time to approx 4uS for internal and external sources. In machine.ADC
reduce sample time to approx 1uS for external source, leave internal at
maximum sampling time.