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ds3231_port.py
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ds3231_port.py
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# FROM HERE: https://github.com/peterhinch/micropython-samples/tree/master/DS3231
# ds3231_port.py Portable driver for DS3231 precison real time clock.
# Adapted from WiPy driver at https://github.com/scudderfish/uDS3231
# Author: Peter Hinch
# Copyright Peter Hinch 2018 Released under the MIT license.
import utime
import machine
import sys
DS3231_I2C_ADDR = 104
try:
rtc = machine.RTC()
except:
print('Warning: machine module does not support the RTC.')
rtc = None
def bcd2dec(bcd):
return (((bcd & 0xf0) >> 4) * 10 + (bcd & 0x0f))
def dec2bcd(dec):
tens, units = divmod(dec, 10)
return (tens << 4) + units
def tobytes(num):
return num.to_bytes(1, 'little')
class DS3231:
def __init__(self, i2c):
self.ds3231 = i2c
self.timebuf = bytearray(7)
if DS3231_I2C_ADDR not in self.ds3231.scan():
raise RuntimeError(
"DS3231 not found on I2C bus at %d" % DS3231_I2C_ADDR)
def get_time(self, set_rtc=False):
if set_rtc:
self.await_transition() # For accuracy set RTC immediately after a seconds transition
else:
self.ds3231.readfrom_mem_into(
DS3231_I2C_ADDR, 0, self.timebuf) # don't wait
return self.convert(set_rtc)
def convert(self, set_rtc=False): # Return a tuple in localtime() format (less yday)
data = self.timebuf
ss = bcd2dec(data[0])
mm = bcd2dec(data[1])
if data[2] & 0x40:
hh = bcd2dec(data[2] & 0x1f)
if data[2] & 0x20:
hh += 12
else:
hh = bcd2dec(data[2])
wday = data[3]
DD = bcd2dec(data[4])
MM = bcd2dec(data[5] & 0x1f)
YY = bcd2dec(data[6])
if data[5] & 0x80:
YY += 2000
else:
YY += 1900
# Time from DS3231 in time.localtime() format (less yday)
result = YY, MM, DD, hh, mm, ss, wday, 0
if set_rtc:
if rtc is None:
# Best we can do is to set local time
secs = utime.mktime(result)
utime.localtime(secs)
else:
rtc.datetime((YY, MM, DD, wday, hh, mm, ss, 0))
return result
def save_time(self, t):
(YY, MM, mday, hh, mm, ss, wday, yday) = t
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 0, tobytes(dec2bcd(ss)))
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 1, tobytes(dec2bcd(mm)))
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 2, tobytes(
dec2bcd(hh))) # Sets to 24hr mode
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 3, tobytes(
dec2bcd(wday))) # 0 == Monday, 6 == Sunday
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 4, tobytes(
dec2bcd(mday))) # Day of month
if YY >= 2000:
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 5, tobytes(
dec2bcd(MM) | 0b10000000)) # Century bit
self.ds3231.writeto_mem(
DS3231_I2C_ADDR, 6, tobytes(dec2bcd(YY-2000)))
else:
self.ds3231.writeto_mem(DS3231_I2C_ADDR, 5, tobytes(dec2bcd(MM)))
self.ds3231.writeto_mem(
DS3231_I2C_ADDR, 6, tobytes(dec2bcd(YY-1900)))
# Wait until DS3231 seconds value changes before reading and returning data
def await_transition(self):
self.ds3231.readfrom_mem_into(DS3231_I2C_ADDR, 0, self.timebuf)
ss = self.timebuf[0]
while ss == self.timebuf[0]:
self.ds3231.readfrom_mem_into(DS3231_I2C_ADDR, 0, self.timebuf)
return self.timebuf
# Test hardware RTC against DS3231. Default runtime 10 min. Return amount
# by which DS3231 clock leads RTC in PPM or seconds per year.
# Precision is achieved by starting and ending the measurement on DS3231
# one-seond boundaries and using ticks_ms() to time the RTC.
# For a 10 minute measurement +-1ms corresponds to 1.7ppm or 53s/yr. Longer
# runtimes improve this, but the DS3231 is "only" good for +-2ppm over 0-40C.
def rtc_test(self, runtime=600, ppm=False, verbose=True):
if rtc is None:
raise RuntimeError('machine.RTC does not exist')
verbose and print('Waiting {} minutes for result'.format(runtime//60))
factor = 1_000_000 if ppm else 114_155_200 # seconds per year
self.await_transition() # Start on transition of DS3231. Record time in .timebuf
t = utime.ticks_ms() # Get system time now
ss = rtc.datetime()[6] # Seconds from system RTC
while ss == rtc.datetime()[6]:
pass
ds = utime.ticks_diff(utime.ticks_ms(), t) # ms to transition of RTC
# Time when transition occurred
ds3231_start = utime.mktime(self.convert())
t = rtc.datetime()
rtc_start = utime.mktime(
(t[0], t[1], t[2], t[4], t[5], t[6], t[3], 0)) # y m d h m s wday 0
utime.sleep(runtime) # Wait a while (precision doesn't matter)
self.await_transition() # of DS3231 and record the time
t = utime.ticks_ms() # and get system time now
ss = rtc.datetime()[6] # Seconds from system RTC
while ss == rtc.datetime()[6]:
pass
de = utime.ticks_diff(utime.ticks_ms(), t) # ms to transition of RTC
# Time when transition occurred
ds3231_end = utime.mktime(self.convert())
t = rtc.datetime()
# y m d h m s wday 0
rtc_end = utime.mktime((t[0], t[1], t[2], t[4], t[5], t[6], t[3], 0))
d_rtc = 1000 * (rtc_end - rtc_start) + de - ds # ms recorded by RTC
d_ds3231 = 1000 * (ds3231_end - ds3231_start) # ms recorded by DS3231
ratio = (d_ds3231 - d_rtc) / d_ds3231
ppm = ratio * 1_000_000
verbose and print(
'DS3231 leads RTC by {:4.1f}ppm {:4.1f}mins/yr'.format(ppm, ppm*1.903))
return ratio * factor
def _twos_complement(self, input_value: int, num_bits: int) -> int:
mask = 2 ** (num_bits - 1)
return -(input_value & mask) + (input_value & ~mask)
def get_temperature(self):
t = self.ds3231.readfrom_mem(DS3231_I2C_ADDR, 0x11, 2)
i = t[0] << 8 | t[1]
return self._twos_complement(i >> 6, 10) * 0.25