Methods implemented are:
- rtc.init(date)
- rtc.datetime([new_date])
- rtc.calibration(value)
The presence of this class can be controlled by MICROPY_PY_MACHINE_RTC. If
the RTC module is used, the time module uses the RTC as well.
For boards without a 32kHz crystal, using RTC makes no sense, since it will
then use the ULP32K oscillator, which is not precise at all. Therefore, it
will by default only be enabled for boards using a crystal, but can be
enabled in the respective mpconfigboard.h.
Which just sets the CPU clock to 200kHz and switches the peripheral clock
off. There are two modes:
machine.lightsleep(duration_ms)
and
machine.lightsleep()
In any mode any configured pin.irq() event will terminate the sleep.
Current consumption in lightsleep for some boards:
- 1.5 - 2.5 mA when supplied trough an active USB
(Seeed XIAO w/o power LED, Adafruit ItsyBitsy)
- 0.8 - 2 mA when supplied through Gnd/+5V (Vusb)
(Seeed XIAO w/o power LED, Adafruit ItsyBitsy)
- < 1 mA for SAMD51 when supplied trough a battery connector
(Sparkfun Thing SAMD51 plus)
Related change: move the calls to SysTick_Config() into set_cpu_freq(). It
is required after each CPU freq change to have ticks_ms run at the proper
rate.
The value given for machine.freq(f) is extend to the range of 1_000_000 to
200_000_000. Frequencies below 48 MHz will be forced to an integer
fraction of 48 MHz. At frequencies below 8 MHz USB is switched off. The
power consumption e.g. of ADAFRUIT_ITSYBITSY_M4_EXPRESS drops to about
1.5 mA at 1 MHz.
Since the peripheral frequency is dropped as well, timing e.g. of PWM,
UART, I2C and SPI is affected and frequency/baud rate has to set again
after a frequency change below 48 MHz.
Two new compile flags are:
MICROPY_HW_DFLL_USB_SYNC: Effective only if DFLL48 does not run from the
crystal. It will synchronize the DFLL48M clock with the USB's SOF pulse.
If no USB is connected, it will fall back to open loop mode. The DFLL48M
clock is then pretty precise, but with a higher clock jitter at SAMD51
devices.
MICROPY_HW_MCU_OSC32KULP: Effective only if the devics uses a crystal as
clock source. Run the MCU clock from the ULP 32kHz oszillator instead of
the crystal. This flag was added to cater for a interference problem of
the crystal and Neopixel/Debug pins at Adafruit FEATHER Mx boards, which
causes the board to crash. Drawback: ticks_ms() and time.time() vs. than
ticks_us() and the peripherals like PWM run at not synchronous clocks.
