wasp: Add battery support

TODO.md

@@ -36,5 +36,5 @@ The TODO list helps keep track on progress towards that goal. It is not
    - [ ] Optimized RLE inner loops
  * [X] Backlight driver
  * [ ] Button driver (interrupt based)
- * [ ] Battery/charger driver
+ * [X] Battery/charger driver
  * [ ] Simple clock and battery level application

manifest/pinetime.py

@@ -2,6 +2,8 @@ freeze('$(MPY_DIR)/../wasp',
     (
         'boot.py',
         'demo.py',
+        'drivers/battery.py',
+        'drivers/signal.py',
         'drivers/st7789.py',
         'logo.py',
         'pinetime.py'

wasp/drivers/battery.py

@@ -0,0 +1,36 @@
+# Generic lithium ion battery driver
+
+from machine import Pin, ADC
+
+class Battery(object):
+    def __init__(self, battery, charging, power=None):
+        self._battery = ADC(battery)
+        self._charging = charging
+        self._power = power
+
+    def charging(self):
+        return self._charging.value() 
+
+    def power(self):
+        if self._power:
+            return self._power.value()
+        return self._charging.value()
+
+    def voltage_mv(self):
+        # Assumes a 50/50 voltage divider and a 3.3v power supply
+        raw = self._battery.read_u16()
+        return (2 * 3300 * raw) // 65535
+
+    def level(self):
+        # This is a trivial battery level estimation approach. It is assumes
+        # the discharge from 4v to 3.5v is roughly linear and 4v is 100% and
+        # that 3.5v is 5%. Below 3.5v the voltage will start to drop pretty
+        # sharply to we will drop from 5% to 0% pretty fast... but we'll
+        # live with that for now.
+        mv = self.voltage_mv()
+        level = ((19 * mv) // 100) - 660
+        if level > 100:
+            return 100
+        if level < 0:
+            return 0
+        return level

wasp/drivers/signal.py

@@ -0,0 +1,23 @@
+class Signal(object):
+    '''Simplified Signal class
+
+    Note: The normal C implementation isn't working for the NRF port
+    '''
+
+    def __init__(self, pin, invert=False):
+        self.pin = pin
+        self.invert = invert
+
+    def __call__(self, v=None):
+        return self.value(v)
+
+    def value(self, v=None):
+        if v == None:
+            return self.invert ^ self.pin.value()
+        self.pin.value(self.invert ^ bool(v))
+
+    def on(self):
+        self.value(1)
+
+    def off(self):
+        self.value(0)

wasp/pinetime.py

@@ -1,6 +1,9 @@
 from machine import Pin
+#from machine import Signal
 from machine import SPI
 
+from drivers.battery import Battery
+from drivers.signal import Signal
 from drivers.st7789 import ST7789_SPI
 
 class Display(ST7789_SPI):
@@ -42,5 +45,9 @@ class Backlight(object):
 
 backlight = Backlight(0)
 display = Display()
-
 backlight.set(1)
+
+battery = Battery(
+        Pin('BATTERY', Pin.IN),
+        Signal(Pin('CHARGING', Pin.IN), invert=True),
+        Signal(Pin('USB_PWR', Pin.IN), invert=True))