def _decode_sensor_type(data):
header = data[0]
remaining_data = data[1:]
# nob, number of offset bytes
nob = (header & 0b11000000) >> 6
if nob:
error = "nob {} != 0 not allowed for Clair ERS sensors".format(nob)
raise t.PayloadContentException(error)
sensor_type = header & 0b00111111
if sensor_type not in _DATA_DECODING_FUNCTIONS:
raise t.PayloadContentException(
"unsupported sensor type: {}".format(sensor_type))
return (nob, sensor_type, remaining_data)
def _decode_measurements(data: bytes):
version, message_id, message_header, data = _decode_header(data)
if version != 0:
raise t.PayloadContentException("unsupported version number: {}".format(version))
if message_id != 0:
raise t.PayloadContentException("unsupported message id: {}".format(message_id))
sample_count = message_header + 1
measurements = _decode_sample_bytes(data)
if len(measurements) != sample_count:
raise t.PayloadContentException("incorrect sample count: {}".format(sample_count))
return measurements
def _decode_co2(data):
if len(data) < 2:
raise t.PayloadFormatException("less than two bytes to decode co2")
co2_bytes = data[0:2]
remaining_data = data[2:]
co2_value = int.from_bytes(co2_bytes, byteorder='big')
if co2_value > 10000:
raise t.PayloadContentException("co2 {} > 10000".format(co2_value))
co2 = t.CO2(co2_value)
return (co2, remaining_data)
def _decode_humidity(data):
if not data:
raise t.PayloadFormatException("no byte to decode relative humidity")
humidity_value = data[0]
remaining_data = data[1:]
if humidity_value > 100:
raise t.PayloadContentException(
"relative humidity {} > 100".format(humidity_value))
humidity = t.RelativeHumidity(humidity_value)
return (humidity, remaining_data)
def _decode_temperature(data):
if len(data) < 2:
raise t.PayloadFormatException(
"less than two bytes to decode temperature")
temperature_bytes = data[0:2]
remaining_data = data[2:]
temperature_value = int.from_bytes(
temperature_bytes, byteorder='big', signed=True) / 10
if temperature_value < -3276.5 or temperature_value > 3276.5:
raise t.PayloadContentException(
"temperature {} not in admissible range")
temperature = t.Temperature(temperature_value)
return (temperature, remaining_data)
def _to_samples(measurements, rx_datetime):
# Let's check the payload's content:
# ERS payloads must contain CO2 measurements.
# The number of CO2 measurements must be conforming to the payload spec.
# They may contain temperature and humidity.
# The number of temperature and humidity measurements is either 0 or equal
# to the number of CO2 measurements.
# All measurements are sorted in reverse-chronological order (LIFO).
# The order within a CO2/temperature/humidity sample group does not matter.
# This is ok: [C, T, H, H, T, C, T, H, C]
# This is inadmissible: [C, C, C, T, T, T, H, H, H]
sample_count = len([m for m in measurements if type(m) == t.CO2])
valid_sample_counts = {
ps.measurement_count
for ps in PROTOCOL_PAYLOAD_SPECIFICATION.values()
}
if not sample_count in valid_sample_counts:
raise t.PayloadContentException(
"invalid number of measurements samples: {}".format(sample_count))
# number of measurements per sample group, either 1 or 3
n = int(len(measurements) / sample_count)
if n != 1 and n != 3:
raise t.PayloadContentException(
"invalid number of measurements: {}".format(len(measurements)))
# split measurements in sub lists of equal size n
sample_groups = [
measurements[i:i + n] for i in range(0, len(measurements), n)
]
# check for exactly one CO2 measurement in each sample group
if not all([
len([m for m in sg if type(m) == t.CO2]) == 1
for sg in sample_groups
]):
raise t.PayloadContentException("invalid order of measurements")
# check for either exactly one or zero temperature/humidity measurement
t_counts = [
len([m for m in sg if type(m) == t.Temperature])
for sg in sample_groups
]
h_counts = [
len([m for m in sg if type(m) == t.RelativeHumidity])
for sg in sample_groups
]
if not ((all([c == 1 for c in t_counts]) and all([c == 1 for c in h_counts])) or \
(all([c == 0 for c in t_counts]) and all([c == 0 for c in h_counts]))):
raise t.PayloadContentException("invalid combination of measurements")
rx_timestamp = round(rx_datetime.timestamp())
# the measurement interval is determined by the number of samples per message
measurement_interval = next(ps.measurement_interval for ps in PROTOCOL_PAYLOAD_SPECIFICATION.values() \
if ps.measurement_count == sample_count)
samples = [
t.Sample(
timestamp=t.Timestamp(rx_timestamp - i * measurement_interval),
co2=next(m for m in sg if type(m) == t.CO2),
temperature=next((m
for m in sg if type(m) == t.Temperature), None),
relative_humidity=next(
(m for m in sg if type(m) == t.RelativeHumidity), None))
for i, sg in enumerate(sample_groups)
]
# return in chronological order
samples.reverse()
return samples