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82 lines
2.4 KiB
Python
82 lines
2.4 KiB
Python
import os
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import fcntl
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import ctypes
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# I2C constants from /usr/include/linux/i2c-dev.h
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I2C_SLAVE = 0x0703
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I2C_SLAVE_FORCE = 0x0706
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I2C_SMBUS = 0x0720
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# SMBus transfer types
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I2C_SMBUS_READ = 1
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I2C_SMBUS_WRITE = 0
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I2C_SMBUS_BYTE_DATA = 2
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I2C_SMBUS_I2C_BLOCK_DATA = 8
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I2C_SMBUS_BLOCK_MAX = 32
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class _I2cSmbusData(ctypes.Union):
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_fields_ = [
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("byte", ctypes.c_uint8),
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("word", ctypes.c_uint16),
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("block", ctypes.c_uint8 * (I2C_SMBUS_BLOCK_MAX + 2)),
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]
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class _I2cSmbusIoctlData(ctypes.Structure):
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_fields_ = [
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("read_write", ctypes.c_uint8),
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("command", ctypes.c_uint8),
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("size", ctypes.c_uint32),
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("data", ctypes.POINTER(_I2cSmbusData)),
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]
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class SMBus:
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def __init__(self, bus: int):
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self._fd = os.open(f'/dev/i2c-{bus}', os.O_RDWR)
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def __enter__(self) -> 'SMBus':
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return self
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def __exit__(self, *args) -> None:
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self.close()
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def close(self) -> None:
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if hasattr(self, '_fd') and self._fd >= 0:
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os.close(self._fd)
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self._fd = -1
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def _set_address(self, addr: int, force: bool = False) -> None:
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ioctl_arg = I2C_SLAVE_FORCE if force else I2C_SLAVE
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fcntl.ioctl(self._fd, ioctl_arg, addr)
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def _smbus_access(self, read_write: int, command: int, size: int, data: _I2cSmbusData) -> None:
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ioctl_data = _I2cSmbusIoctlData(read_write, command, size, ctypes.pointer(data))
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fcntl.ioctl(self._fd, I2C_SMBUS, ioctl_data)
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def read_byte_data(self, addr: int, register: int, force: bool = False) -> int:
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self._set_address(addr, force)
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data = _I2cSmbusData()
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self._smbus_access(I2C_SMBUS_READ, register, I2C_SMBUS_BYTE_DATA, data)
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return int(data.byte)
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def write_byte_data(self, addr: int, register: int, value: int, force: bool = False) -> None:
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self._set_address(addr, force)
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data = _I2cSmbusData()
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data.byte = value & 0xFF
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self._smbus_access(I2C_SMBUS_WRITE, register, I2C_SMBUS_BYTE_DATA, data)
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def read_i2c_block_data(self, addr: int, register: int, length: int, force: bool = False) -> list[int]:
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self._set_address(addr, force)
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if not (0 <= length <= I2C_SMBUS_BLOCK_MAX):
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raise ValueError(f"length must be 0..{I2C_SMBUS_BLOCK_MAX}")
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data = _I2cSmbusData()
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data.block[0] = length
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self._smbus_access(I2C_SMBUS_READ, register, I2C_SMBUS_I2C_BLOCK_DATA, data)
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read_len = int(data.block[0]) or length
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read_len = min(read_len, length)
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return [int(b) for b in data.block[1 : read_len + 1]]
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