kopia lustrzana https://github.com/peterhinch/micropython-samples
ds3231_gen: move setting RTC from code to docs.
peterhinch
rodzic
14ebf88797
commit
6c478601a6
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@ -21,9 +21,27 @@ the DS3231. This enables relatively rapid accuracy testing of the platform's
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RTC, and fast calibration of the Pyboard's RTC. To quantify this, a
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sufficiently precise value of calibration may be acquired in 5-10 minutes.
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# Datetime tuples
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MicroPython currently enjoys three formats. The first is that used by the
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`time` module in `localtime` and `gmtime`. This is
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`(year, month, mday, hour, minute, second, weekday, yearday)`
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with the meaning of each field as described in the
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[MP official docs](http://docs.micropython.org/en/latest/library/time.html#functions) and
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[CPython docs](https://docs.python.org/3/library/time.html#time.struct_time).
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**These drivers use this format as it is the CPython standard.**
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The micropython RTC class uses [this format](http://docs.micropython.org/en/latest/library/machine.RTC.html#machine.RTC.init)
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in its `__init__` method:
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`(year, month, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]])`
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and this format in its `datetime` method:
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`(year, month, mday, weekday, hours, minutes, seconds, subseconds)`
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It is to be hoped that some standardisation will occur. Please check official
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docs for any changes.
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###### [Main README](../README.md)
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# 1. General purpose driver ds3231_gen.py
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# 1. General purpose driver ds3231_gen
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This uses datetime tuples to set and read time values. These are of form
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(year, month, day, hour, minute, second, weekday, yearday)
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@ -35,12 +53,8 @@ as used by [time.localtime](http://docs.micropython.org/en/latest/library/time.h
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This takes one mandatory argument, an initialised I2C bus.
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#### Public methods:
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1. `get_time(set_rtc=False)`. If `set_rtc` is `True` it sets the platform's
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RTC from the DS3231. Returns the DS3231 time as a datetime tuple with
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1. `get_time()`. Returns the DS3231 time as a datetime tuple with
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`yearday=0`.
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On ports/platforms which don't support an RTC, if `set_rtc` is `True`, the
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system time will be set from the DS3231. If setting the RTC, for accuracy the
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method will pause until a seconds transition occurs on the DS3231.
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2. `set_time(tt=None)`. Sets the DS3231 time. By default it uses the
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platform's syatem time, otherwise the passed `datetime` tuple. If passing a
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tuple, see the note below.
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@ -72,7 +86,7 @@ This takes one mandatory argument, an initialised I2C bus.
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#### Module constants
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These are the allowable options for the alarm's `when` arg, along with the
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relevant `Alarm.set()` args:
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relevant `Alarm.set()` args:
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`EVERY_SECOND` Only supported by alarm1.
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`EVERY_MINUTE` `sec`
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`EVERY_HOUR` `min`, `sec`
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@ -97,7 +111,8 @@ def dt_tuple(dt):
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#### Alarms
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Comments assume that a backup battery is in use.
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Comments assume that a backup battery is in use, in which case alarms continue
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to operate.
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The battery ensures that alarm settings are stored through a power outage. If
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an alarm occurs during an outage the pin will be driven low and will stay low
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@ -110,10 +125,10 @@ from machine import SoftI2C, Pin
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from ds3231_gen import *
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i2c = SoftI2C(scl=Pin(16, Pin.OPEN_DRAIN, value=1), sda=Pin(17, Pin.OPEN_DRAIN, value=1))
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d = DS3231(i2c)
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dt.alarm1.set(EVERY_MINUTE, sec=30)
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dt.alarm1.set(EVERY_MINUTE, sec=30) # Alarm on the half minute
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```
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If a power outage occurs here the following code will ensure alarms continue to
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occur at one minute intervals:
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If a power outage occurs here the following code demonstrates that alarms
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continue to occur at one minute intervals:
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```python
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from machine import SoftI2C, Pin
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from ds3231_gen import *
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@ -132,6 +147,47 @@ Re the `INT\` (alarm) pin the datasheet (P9) states "The pullup voltage can be
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up to 5.5V, regardless of the voltage on Vcc". Note that some breakout boards
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have a pullup resistor between this pin and Vcc.
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#### Setting system RTC
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Note that the DS3231 driver uses the CPython standard datetime tuple:
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`(year, month, mday, hour, minute, second, weekday, yearday)`
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Currently the RTC `datetime` method uses a different format.
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The system RTC may be set from the DS3231 as follows:
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```python
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from machine import SoftI2C, Pin, RTC
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from ds3231_gen import *
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i2c = SoftI2C(scl=Pin(16, Pin.OPEN_DRAIN, value=1), sda=Pin(17, Pin.OPEN_DRAIN, value=1))
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d = DS3231(i2c)
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rtc = RTC()
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YY, MM, DD, hh, mm, ss, wday, _ = d.get_time()
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rtc.datetime((YY, MM, DD, wday, hh, mm, ss, 0))
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```
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The following can be used to set the RTC to better than +-1s accuracy. Though
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the DS3231 has only 1s resolution, setting the RTC on a transition of the
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seconds value minimises error.
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```python
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t = d.get_time() # As per above, d is the DS3231 instance
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while t == d.get_time()[5]: # Wait for change in seconds
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pass
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YY, MM, DD, hh, mm, ss, wday, _ = t # Set time now
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rtc.datetime((YY, MM, DD, wday, hh, mm, ss, 0))
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```
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#### Application: micropower systems
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The DS3231 alarm pin may be used to control the application of power to the
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MicroPython host and peripheral devices. This may be done with a PNP transistor
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driven (via suitable resistors) from the alarm output. When in an alarm state,
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power is applied to the system. The DS3231 is set to alarm at the required
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interval - say at 00:03:00 every Sunday. On startup the system takes readings
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and logs them or reports them via MQTT. Its final act is to issue
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```python
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ds3231.alarm1.clear()
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```
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which turns off the MOSFET and the transistor and powers down the system.
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Current in the OFF state will be very much less than 1μA.
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# 2. Portable driver ds3231_port
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This can use soft I2C so any pins may be used.
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@ -71,26 +71,16 @@ class DS3231:
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if _ADDR not in self.ds3231.scan():
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raise RuntimeError(f"DS3231 not found on I2C bus at {_ADDR}")
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def get_time(self, set_rtc=False, data=bytearray(7)):
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def get_time(self, data=bytearray(7)):
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def bcd2dec(bcd): # Strip MSB
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return ((bcd & 0x70) >> 4) * 10 + (bcd & 0x0F)
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self.ds3231.readfrom_mem_into(_ADDR, 0, data)
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if set_rtc: # For accuracy set RTC immediately after a seconds transition
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ss = data[0]
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while ss == data[0]:
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self.ds3231.readfrom_mem_into(_ADDR, 0, data)
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ss, mm, hh, wday, DD, MM, YY = [bcd2dec(x) for x in data]
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MM &= 0x1F # Strip century
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YY += 2000
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# Time from DS3231 in time.localtime() format (less yday)
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result = YY, MM, DD, hh, mm, ss, wday - 1, 0
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if set_rtc:
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if rtc is None: # Best we can do is to set local time
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secs = time.mktime(result)
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time.localtime(secs)
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else:
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rtc.datetime((YY, MM, DD, wday, hh, mm, ss, 0))
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return result
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# Output time or alarm data to device
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