# SPDX-FileCopyrightText: 2016 Scott Shawcroft for Adafruit Industries
#
# SPDX-License-Identifier: MIT
# pylint: disable=too-few-public-methods
"""
`adafruit_register.i2c_bits`
====================================================
Multi bit registers
* Author(s): Scott Shawcroft
"""
__version__ = "0.0.0+auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_Register.git"
try:
from typing import Optional, Type, NoReturn
from circuitpython_typing.device_drivers import I2CDeviceDriver
except ImportError:
pass
[docs]
class RWBits:
"""
Multibit register (less than a full byte) that is readable and writeable.
This must be within a byte register.
Values are `int` between 0 and 2 ** ``num_bits`` - 1.
:param int num_bits: The number of bits in the field.
:param int register_address: The register address to read the bit from
:param int lowest_bit: The lowest bits index within the byte at ``register_address``
:param int register_width: The number of bytes in the register. Defaults to 1.
:param bool lsb_first: Is the first byte we read from I2C the LSB? Defaults to true
:param bool signed: If True, the value is a "two's complement" signed value.
If False, it is unsigned.
"""
def __init__( # pylint: disable=too-many-arguments
self,
num_bits: int,
register_address: int,
lowest_bit: int,
register_width: int = 1,
lsb_first: bool = True,
signed: bool = False,
) -> None:
self.bit_mask = ((1 << num_bits) - 1) << lowest_bit
# print("bitmask: ",hex(self.bit_mask))
if self.bit_mask >= 1 << (register_width * 8):
raise ValueError("Cannot have more bits than register size")
self.lowest_bit = lowest_bit
self.buffer = bytearray(1 + register_width)
self.buffer[0] = register_address
self.lsb_first = lsb_first
self.sign_bit = (1 << (num_bits - 1)) if signed else 0
def __get__(
self,
obj: Optional[I2CDeviceDriver],
objtype: Optional[Type[I2CDeviceDriver]] = None,
) -> int:
with obj.i2c_device as i2c:
i2c.write_then_readinto(self.buffer, self.buffer, out_end=1, in_start=1)
# read the number of bytes into a single variable
reg = 0
order = range(len(self.buffer) - 1, 0, -1)
if not self.lsb_first:
order = reversed(order)
for i in order:
reg = (reg << 8) | self.buffer[i]
reg = (reg & self.bit_mask) >> self.lowest_bit
# If the value is signed and negative, convert it
if reg & self.sign_bit:
reg -= 2 * self.sign_bit
return reg
def __set__(self, obj: I2CDeviceDriver, value: int) -> None:
value <<= self.lowest_bit # shift the value over to the right spot
with obj.i2c_device as i2c:
i2c.write_then_readinto(self.buffer, self.buffer, out_end=1, in_start=1)
reg = 0
order = range(len(self.buffer) - 1, 0, -1)
if not self.lsb_first:
order = range(1, len(self.buffer))
for i in order:
reg = (reg << 8) | self.buffer[i]
# print("old reg: ", hex(reg))
reg &= ~self.bit_mask # mask off the bits we're about to change
reg |= value # then or in our new value
# print("new reg: ", hex(reg))
for i in reversed(order):
self.buffer[i] = reg & 0xFF
reg >>= 8
i2c.write(self.buffer)
[docs]
class ROBits(RWBits):
"""
Multibit register (less than a full byte) that is read-only. This must be
within a byte register.
Values are `int` between 0 and 2 ** ``num_bits`` - 1.
:param int num_bits: The number of bits in the field.
:param int register_address: The register address to read the bit from
:param type lowest_bit: The lowest bits index within the byte at ``register_address``
:param int register_width: The number of bytes in the register. Defaults to 1.
"""
def __set__(self, obj: I2CDeviceDriver, value: int) -> NoReturn:
raise AttributeError()