add noise field to EGVRecords

CC @jasoncalabrese, re https://github.com/openaps/dexcom_reader/issues/12

2 files changed, 5 insertions, 1 deletions

diff --git a/dexcom_reader/constants.py b/dexcom_reader/constants.py
index 421c190..628d325 100644
--- a/dexcom_reader/constants.py
+++ b/dexcom_reader/constants.py
@@ -63,6 +63,7 @@ MAX_POSSIBLE_COMMAND = 255
 EGV_VALUE_MASK = 1023
 EGV_DISPLAY_ONLY_MASK = 32768
 EGV_TREND_ARROW_MASK = 15
+EGV_NOISE_MASK = 112
 
 BATTERY_STATES = [None, 'CHARGING', 'NOT_CHARGING', 'NTC_FAULT', 'BAD_BATTERY']
 
diff --git a/dexcom_reader/database_records.py b/dexcom_reader/database_records.py
index 9274d24..22ba279 100644
--- a/dexcom_reader/database_records.py
+++ b/dexcom_reader/database_records.py
@@ -289,7 +289,7 @@ class SensorRecord(GenericTimestampedRecord):
 class EGVRecord(GenericTimestampedRecord):
   # uint, uint, ushort, byte, ushort
   # (system_seconds, display_seconds, glucose, trend_arrow, crc)
-  FIELDS = ['glucose', 'trend_arrow']
+  FIELDS = ['glucose', 'trend_arrow', 'noise']
   FORMAT = '<2IHcH'
 
   @property
@@ -322,6 +322,9 @@ class EGVRecord(GenericTimestampedRecord):
     arrow_value = ord(self.full_trend) & constants.EGV_TREND_ARROW_MASK
     return constants.TREND_ARROW_VALUES[arrow_value]
 
+  @property
+  def noise (self):
+    return (ord(self.data[3]) & constants.EGV_NOISE_MASK) >> 4
   def __repr__(self):
     if self.is_special:
       return '%s: %s' % (self.display_time, self.glucose_special_meaning)