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reading correct values #26

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merged 1 commit into from
Mar 5, 2023
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reading correct values #26

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13 changes: 8 additions & 5 deletions adafruit_mpl3115a2.py
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Original file line number Diff line number Diff line change
Expand Up @@ -125,7 +125,10 @@ class MPL3115A2:

# Class level buffer to reduce memory usage and allocations.
# Note this is not thread safe by design!
_BUFFER = bytearray(4)
_BUFFER = bytearray(5)
# _BUFFER size was previously 4. It was increased as the current configuration
# creates a flag in _MPL3115A2_REGISTER_STATUS that we were not clearing depending
# on the properties reading order

def __init__(self, i2c, *, address=_MPL3115A2_ADDRESS):
self._device = i2c_device.I2CDevice(i2c, address)
Expand Down Expand Up @@ -209,7 +212,7 @@ def pressure(self):
):
time.sleep(0.01)
# Read 3 bytes of pressure data into buffer.
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER, count=3)
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER)
# Reconstruct 20-bit pressure value.
pressure = (
(self._BUFFER[0] << 16) | (self._BUFFER[1] << 8) | self._BUFFER[2]
Expand Down Expand Up @@ -241,7 +244,7 @@ def altitude(self):
# Read 3 bytes of altitude data into buffer.
# Yes even though this is the address of the pressure register it
# returns altitude when the ALT bit is set above.
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER, count=3)
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER)
# Reconstruct signed 32-bit altitude value (actually 24 bits shifted up
# and then scaled down).
self._BUFFER[3] = 0 # Top 3 bytes of buffer were read from the chip.
Expand All @@ -264,9 +267,9 @@ def temperature(self):
):
time.sleep(0.01)
# Read 2 bytes of data from temp register.
self._read_into(_MPL3115A2_REGISTER_TEMP_MSB, self._BUFFER, count=2)
self._read_into(_MPL3115A2_REGISTER_PRESSURE_MSB, self._BUFFER)
# Reconstruct signed 12-bit value.
temperature = struct.unpack(">h", self._BUFFER[0:2])[0]
temperature = struct.unpack(">h", self._BUFFER[3:5])[0]
temperature >>= 4
# Scale down to degrees Celsius.
return temperature / 16.0
Expand Down