def start(self):
# Main operating loop
while not self._exit_flag:
try:
# Polls until ready
while not(self._is_ready()):
time.sleep(0.1)
# Sample sps30
read = self._read_data()
# Check crc8 and deserialize
for i in range(0, 10):
# crc8 check
assert calc_crc8(read[i * 6 : i * 6 + 2]) == bytes([read[i * 6 + 2]]), "Bad upper crc8"
assert calc_crc8(read[i * 6 + 3: i * 6 + 5]) == bytes([read[i * 6 + 5]]), "Bad lower crc8"
# Deserialize
float_struct = struct.pack('>BBBB', read[i * 6], read[i * 6 + 1], read[i * 6 + 3], read[i * 6 + 4])
self._curr_data[i] = struct.unpack('>f', float_struct)[0]
# Sleep timer
time.sleep(self._interval)
except Exception as e:
# Reset sensor in case I2C Bus fail, bad crc8, whatever
print(e)
self._reset()
time.sleep(3)
def _is_ready(self):
# Returns device ready flag
self._i2c.writeto(SCD30_I2C_ID, SCD30_READY_ADDR)
read = self._i2c.readfrom(SCD30_I2C_ID, 3)
return bytes([read[2]]) == calc_crc8(read[0:2])
def startMeasurement(self):
cmd = bytearray([
0x00, 0x10, 0x03, 0x00,
crc8.calc_crc8([0x03, 0x00], self.crc_init, self.crc_poly)
])
with self.i2c_device as i2c:
i2c.write(cmd)
def _send_start(self):
# Start measurement mode, returns number of bytes written
return self._i2c.writeto(
SCD30_I2C_ID, SCD30_START_ADDR + SCD30_START_MEASUREMENT +
calc_crc8(SCD30_START_MEASUREMENT))