Source code for adafruit_onewire.bus

# SPDX-FileCopyrightText: 2017 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT

"""
`adafruit_onewire.bus`
====================================================

Provide access to a 1-Wire bus.

* Author(s): Carter Nelson
"""

__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_OneWire.git"

import busio
from micropython import const

_SEARCH_ROM = const(0xF0)
_MATCH_ROM = const(0x55)
_SKIP_ROM = const(0xCC)
_MAX_DEV = const(10)


[docs]class OneWireError(Exception): """A class to represent a 1-Wire exception."""
[docs]class OneWireAddress: """A class to represent a 1-Wire address.""" def __init__(self, rom): self._rom = rom @property def rom(self): """The unique 64 bit ROM code.""" return self._rom @property def crc(self): """The 8 bit CRC.""" return self._rom[7] @property def serial_number(self): """The 48 bit serial number.""" return self._rom[1:7] @property def family_code(self): """The 8 bit family code.""" return self._rom[0]
[docs]class OneWireBus: """A class to represent a 1-Wire bus.""" def __init__(self, pin): # pylint: disable=no-member self._ow = busio.OneWire(pin) self._readbit = self._ow.read_bit self._writebit = self._ow.write_bit self._maximum_devices = _MAX_DEV @property def maximum_devices(self): """The maximum number of devices the bus will scan for. Valid range is 1 to 255. It is an error to have more devices on the bus than this number. Having less is OK. """ return self._maximum_devices @maximum_devices.setter def maximum_devices(self, count): if not isinstance(count, int): raise ValueError("Maximum must be an integer value 1 - 255.") if count < 1 or count > 0xFF: raise ValueError("Maximum must be an integer value 1 - 255.") self._maximum_devices = count
[docs] def reset(self, required=False): """ Perform a reset and check for presence pulse. :param bool required: require presence pulse """ reset = self._ow.reset() if required and reset: raise OneWireError("No presence pulse found. Check devices and wiring.") return not reset
[docs] def readinto(self, buf, *, start=0, end=None): """ Read into ``buf`` from the device. The number of bytes read will be the length of ``buf``. If ``start`` or ``end`` is provided, then the buffer will be sliced as if ``buf[start:end]``. This will not cause an allocation like ``buf[start:end]`` will so it saves memory. :param bytearray buf: buffer to write into :param int start: Index to start writing at :param int end: Index to write up to but not include """ if end is None: end = len(buf) for i in range(start, end): buf[i] = self._readbyte()
[docs] def write(self, buf, *, start=0, end=None): """ Write the bytes from ``buf`` to the device. If ``start`` or ``end`` is provided, then the buffer will be sliced as if ``buffer[start:end]``. This will not cause an allocation like ``buffer[start:end]`` will so it saves memory. :param bytearray buf: buffer containing the bytes to write :param int start: Index to start writing from :param int end: Index to read up to but not include """ if end is None: end = len(buf) for i in range(start, end): self._writebyte(buf[i])
[docs] def scan(self): """Scan for devices on the bus and return a list of addresses.""" devices = [] diff = 65 rom = False count = 0 for _ in range(0xFF): rom, diff = self._search_rom(rom, diff) if rom: count += 1 if count > self.maximum_devices: raise RuntimeError( "Maximum device count of {} exceeded.".format( self.maximum_devices ) ) devices.append(OneWireAddress(rom)) if diff == 0: break return devices
def _readbyte(self): val = 0 for i in range(8): val |= self._ow.read_bit() << i return val def _writebyte(self, value): for i in range(8): bit = (value >> i) & 0x1 self._ow.write_bit(bit) def _search_rom(self, l_rom, diff): if not self.reset(): return None, 0 self._writebyte(_SEARCH_ROM) if not l_rom: l_rom = bytearray(8) rom = bytearray(8) next_diff = 0 i = 64 for byte in range(8): r_b = 0 for bit in range(8): b = self._readbit() if self._readbit(): if b: # there are no devices or there is an error on the bus return None, 0 else: if not b: # collision, two devices with different bit meaning if diff > i or ((l_rom[byte] & (1 << bit)) and diff != i): b = 1 next_diff = i self._writebit(b) r_b |= b << bit i -= 1 rom[byte] = r_b return rom, next_diff
[docs] @staticmethod def crc8(data): """ Perform the 1-Wire CRC check on the provided data. :param bytearray data: 8 byte array representing 64 bit ROM code """ crc = 0 for byte in data: crc ^= byte for _ in range(8): if crc & 0x01: crc = (crc >> 1) ^ 0x8C else: crc >>= 1 crc &= 0xFF return crc