primitives/aadc.py

   1 # aadc.py AADC (asynchronous ADC) class
   2
   3 # Copyright (c) 2020 Peter Hinch
   4 # Released under the MIT License (MIT) - see LICENSE file
   5
   6 import uasyncio as asyncio
   7 import io
   8
   9 MP_STREAM_POLL_RD = const(1)
  10 MP_STREAM_POLL = const(3)
  11 MP_STREAM_ERROR = const(-1)
  12
  13 class AADC(io.IOBase):
  14     def __init__(self, adc):
  15         self._adc = adc
  16         self._lower = 0
  17         self._upper = 65535
  18         self._pol = True
  19         self._last = None
  20         self._sreader = asyncio.StreamReader(self)
  21
  22     def __iter__(self):
  23         b = yield from self._sreader.read(2)
  24         return int.from_bytes(b, 'little')
  25
  26     def _adcread(self):
  27         self._last = self._adc.read_u16()
  28         return self._last
  29
  30     def read(self, n):  # For use by StreamReader only
  31         return int.to_bytes(self._last, 2, 'little')
  32
  33     def ioctl(self, req, arg):
  34         ret = MP_STREAM_ERROR
  35         if req == MP_STREAM_POLL:
  36             ret = 0
  37             if arg & MP_STREAM_POLL_RD:
  38                 if self._pol ^ (self._lower <= self._adcread() <= self._upper):
  39                     ret |= MP_STREAM_POLL_RD
  40         return ret
  41
  42     # *** API ***
  43
  44     # If normal will pause until ADC value is in range
  45     # Otherwise will pause until value is out of range
  46     def sense(self, normal):
  47         self._pol = normal
  48
  49     def read_u16(self, last=False):
  50         if last:
  51             return self._last
  52         return self._adcread()
  53
  54     # Call syntax: set limits for trigger
  55     # lower is None: leave limits unchanged.
  56     # upper is None: treat lower as relative to current value.
  57     # both have values: treat as absolute limits.
  58     def __call__(self, lower=None, upper=None):
  59         if lower is not None:
  60             if upper is None:  # Relative limit
  61                 r = self._adcread() if self._last is None else self._last
  62                 self._lower = r - lower
  63                 self._upper = r + lower
  64             else:  # Absolute limits
  65                 self._lower = lower
  66                 self._upper = upper
  67         return self