fixes for cpython & pi: hard reset before i2c init, tighten struct.unpack()

It's necessary to hook up the reset pin and toggle it before initializing the i2c
device, at least with some hardware (including the Raspberry Pi).

struct.unpack() is stricter about inputs on CPython than under CircuitPython.

Author: Brennen Bearnes

adafruit_si4713.py

@@ -120,11 +120,24 @@ class SI4713:
 
     def __init__(self, i2c, *, address=_SI4710_ADDR1, reset=None, timeout_s=0.1):
         self._timeout_s = timeout_s
-        self._device = i2c_device.I2CDevice(i2c, address)
+
         # Configure reset line if it was provided.
         self._reset = reset
+
         if self._reset is not None:
             self._reset.switch_to_output(value=True)
+
+            # Toggle reset line low to reset the chip and then wait a bit for 
+            # startup - this is necessary before initializing as an i2c device
+            # on at least the Raspberry Pi, and potentially elsewhere:
+            self._reset.value = True
+            time.sleep(0.01)
+            self._reset.value = False
+            time.sleep(0.01)
+            self._reset.value = True
+            time.sleep(0.25)
+
+        self._device = i2c_device.I2CDevice(i2c, address)
         self.reset()
         # Check product ID.
         if self._get_product_number() != 13:
@@ -382,8 +395,7 @@ def input_level(self):
         """
         # Perform ASQ request, then parse out 8 bit _signed_ input level value.
         self._asq_status()
-        return struct.unpack('bbbbb', self._BUFFER)[4]
-
+        return struct.unpack('bbbbb', self._BUFFER[0:5])[4]
     @property
     def audio_signal_status(self):
         """Retrieve the ASQ or audio signal quality status value from the chip.

examples/simpletest.py

@@ -12,19 +12,24 @@
 # mentions you can only specify 50khz steps!
 FREQUENCY_KHZ = 102300  # 102.300mhz
 
-
 # Initialize I2C bus.
 i2c = busio.I2C(board.SCL, board.SDA)
 
 # Initialize SI4713.
-si4713 = adafruit_si4713.SI4713(i2c)
+# si4713 = adafruit_si4713.SI4713(i2c)
+
 # Alternatively you can specify the I2C address of the device if it changed:
-#si4713 = adafruit_si4713.SI4713(i2c, address=0x11)
-# Also if you hooked up the reset line you can specify that too.  Make sure
-# to pass in a DigitalInOut instance:
-#import digitalio
-#reset = digitalio.DigitalInOut(board.D5)
-#si4713 = adafruit_si4713.SI4713(i2c, reset=reset)
+# si4713 = adafruit_si4713.SI4713(i2c, address=0x11)
+
+# If you hooked up the reset line you should specify that too.  Make sure
+# to pass in a DigitalInOut instance.  You will need the reset pin with the
+# Raspberry Pi, and probably other devices:
+import digitalio
+reset = digitalio.DigitalInOut(board.D5)
+
+print('initializing si4713 instance')
+si4713 = adafruit_si4713.SI4713(i2c, reset=reset, timeout_s=0.5)
+print('done')
 
 # Measure the noise level for the transmit frequency (this assumes automatic
 # antenna capacitance setting, but see below to adjust to a specific value).