Fix proximity read frequency

Previously, the module used an incorrect register to set the proximity
modulator timing of the chip, rather than the number of proximity
reads per second.

This change updates the getter and setter for frequency to use the
correct proximity rate register, and adds a modulation property to
continue to provide access to that register (though it probably should
be left at the default)

Author: stonehippo

adafruit_vcnl4010.py

@@ -55,10 +55,21 @@
 _VCNL4010_AMBIENT_LUX_SCALE = 0.25  # Lux value per 16-bit result value.
 
 # User-facing constants:
-FREQUENCY_3M125 = 3
-FREQUENCY_1M5625 = 2
-FREQUENCY_781K25 = 1
-FREQUENCY_390K625 = 0
+# Number of proximity measuremenrs per second
+FREQUENCY_1_95 = 0
+FREQUENCY_3_90625 = 1
+FREQUENCY_7_8125 = 2
+FREQUENCY_16_625 = 3
+FREQUENCY_31_25 = 4
+FREQUENCY_62_5 = 5
+FREQUENCY_125 = 6
+FREQUENCY_250 = 7
+
+# Proximity modulator timing
+MODULATION_3M125 = 3 
+MODULATION_1M5625 = 2
+MODULATION_781K25 = 1
+MODULATION_390K625 = 0
 
 # Disable pylint's name warning as it causes too much noise.  Suffixes like
 # BE (big-endian) or mA (milli-amps) don't confirm to its conventions--by
@@ -113,7 +124,8 @@ def __init__(self, i2c, address=_VCNL4010_I2CADDR_DEFAULT):
         if (revision & 0xF0) != 0x20:
             raise RuntimeError("Failed to find VCNL4010, check wiring!")
         self.led_current = 20
-        self.frequency = FREQUENCY_390K625
+        self.frequency = FREQUENCY_1_95
+        self.modulation = MODULATION_390K625
         self._write_u8(_VCNL4010_INTCONTROL, 0x08)
 
     def _read_u8(self, address):
@@ -153,8 +165,8 @@ def led_current(self, val):
 
     @property
     def led_current_mA(self):
-        """The current of the LED in milli-amps.  The value here is
-        specified in a milliamps from 0-200.  Note that this value will be
+        """The current of the LED in milliamps.  The value here is
+        specified in milliamps from 0-200.  Note that this value will be
         quantized down to a smaller less-accurate value as the chip only
         supports current changes in 10mA increments, i.e. a value of 123 mA will
         actually use 120 mA.  See the datasheet for how the LED current impacts
@@ -170,20 +182,41 @@ def led_current_mA(self, val):
     @property
     def frequency(self):
         """
-        The frequency of proximity measurements.  Must be a value of:
+        The frequency of proximity measurements per second.  Must be a value of:
+
+        - FREQUENCY_1_95: 1.95 measurements/sec (default)
+        - FREQUENCY_3_90625: 3.90625 measurements/sec
+        - FREQUENCY_7_8125: 7.8125 measurements/sec
+        - FREQUENCY_16_625: 16.625 measurements/sec
+        - FREQUENCY_31_25: 31.25 measurements/sec
+        - FREQUENCY_62_5: 62.5 measurements/sec
+        - FREQUENCY_125: 125 measurements/sec
+        - FREQUENCY_250: 250 measurements/sec
+
+        See the datasheet for how frequency changes the power consumption and
+        proximity detection accuracy.
+        """
+        return self._read_u8(_VCNL4010_PROXRATE)
+
+    @frequency.setter
+    def frequency(self, val):
+        assert 0 <= val <= 7
+        self._write_u8(_VCNL4010_PROXRATE, val)
 
-        - FREQUENCY_3M125: 3.125 Mhz
-        - FREQUENCY_1M5625: 1.5625 Mhz
-        - FREQUENCY_781K25: 781.25 Khz
-        - FREQUENCY_390K625: 390.625 Khz (default)
+    @property
+    def modulation(self):
+        """
+        Proximity modulator timimg.  Must be a value of:
 
-        See the datasheet for how frequency changes the proximity detection
-        accuracy.
+        - MODULATION_3M125: 3.125 Mhz
+        - MODULATION_1M5625: 1.5625 Mhz
+        - MODULATION_781K25: 781.25 Khz
+        - MODULATION_390K625: 390.625 Khz (default)
         """
         return (self._read_u8(_VCNL4010_MODTIMING) >> 3) & 0x03
 
-    @frequency.setter
-    def frequency(self, val):
+    @modulation.setter
+    def modulation(self, val):
         assert 0 <= val <= 3
         timing = self._read_u8(_VCNL4010_MODTIMING)
         timing &= ~0b00011000