404 lines
11 KiB
Python
404 lines
11 KiB
Python
# SPDX-FileCopyrightText: 2020 Melissa LeBlanc-Williams for Adafruit Industries
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#
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# SPDX-License-Identifier: MIT
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"""
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`Adafruit_PureIO.spi`
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================================================================================
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Pure python (i.e. no native extensions) access to Linux IO SPI interface that is
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similar to the SpiDev API. Based heavily on https://github.com/tomstokes/python-spi/.
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* Author(s): Tom Stokes, Melissa LeBlanc-Williams
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Implementation Notes
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--------------------
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**Software and Dependencies:**
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* Linux and Python 3.5 or Higher
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"""
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# imports
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from ctypes import create_string_buffer, string_at, addressof
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from fcntl import ioctl
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import struct
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import platform
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import os.path
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from os import environ
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import array
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__version__ = "1.1.11"
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__repo__ = "https://github.com/adafruit/Adafruit_Python_PureIO.git"
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# SPI C API constants (from linux kernel headers)
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SPI_CPHA = 0x01
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SPI_CPOL = 0x02
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SPI_CS_HIGH = 0x04
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SPI_LSB_FIRST = 0x08
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SPI_THREE_WIRE = 0x10
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SPI_LOOP = 0x20
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SPI_NO_CS = 0x40
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SPI_READY = 0x80
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SPI_TX_DUAL = 0x100
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SPI_TX_QUAD = 0x200
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SPI_RX_DUAL = 0x400
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SPI_RX_QUAD = 0x800
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SPI_MODE_0 = 0
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SPI_MODE_1 = SPI_CPHA
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SPI_MODE_2 = SPI_CPOL
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SPI_MODE_3 = SPI_CPHA | SPI_CPOL
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SPI_DEFAULT_CHUNK_SIZE = 4096
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def _ioc_encode(direction, number, structure):
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"""
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ioctl command encoding helper function
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Calculates the appropriate spidev ioctl op argument given the direction,
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command number, and argument structure in python's struct.pack format.
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Returns a tuple of the calculated op and the struct.pack format
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See Linux kernel source file /include/uapi/asm/ioctl.h
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"""
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ioc_magic = ord("k")
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ioc_nrbits = 8
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ioc_typebits = 8
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if platform.machine() == "mips":
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ioc_sizebits = 13
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else:
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ioc_sizebits = 14
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ioc_nrshift = 0
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ioc_typeshift = ioc_nrshift + ioc_nrbits
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ioc_sizeshift = ioc_typeshift + ioc_typebits
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ioc_dirshift = ioc_sizeshift + ioc_sizebits
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size = struct.calcsize(structure)
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operation = (
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(direction << ioc_dirshift)
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| (ioc_magic << ioc_typeshift)
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| (number << ioc_nrshift)
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| (size << ioc_sizeshift)
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)
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return direction, operation, structure
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# pylint: disable=too-many-instance-attributes, too-many-branches
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class SPI:
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"""
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This class is similar to SpiDev, but instead of opening and closing
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for each call, it is set up on initialization making it fast.
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"""
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_IOC_TRANSFER_FORMAT = "QQIIHBBBBH"
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if platform.machine() == "mips":
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# Direction is 3 bits
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_IOC_READ = 2
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_IOC_WRITE = 4
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else:
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# Direction is 2 bits
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_IOC_WRITE = 1
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_IOC_READ = 2
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# _IOC_MESSAGE is a special case, so we ony need the ioctl operation
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_IOC_MESSAGE = _ioc_encode(_IOC_WRITE, 0, _IOC_TRANSFER_FORMAT)[1]
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_IOC_RD_MODE = _ioc_encode(_IOC_READ, 1, "B")
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_IOC_WR_MODE = _ioc_encode(_IOC_WRITE, 1, "B")
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_IOC_RD_LSB_FIRST = _ioc_encode(_IOC_READ, 2, "B")
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_IOC_WR_LSB_FIRST = _ioc_encode(_IOC_WRITE, 2, "B")
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_IOC_RD_BITS_PER_WORD = _ioc_encode(_IOC_READ, 3, "B")
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_IOC_WR_BITS_PER_WORD = _ioc_encode(_IOC_WRITE, 3, "B")
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_IOC_RD_MAX_SPEED_HZ = _ioc_encode(_IOC_READ, 4, "I")
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_IOC_WR_MAX_SPEED_HZ = _ioc_encode(_IOC_WRITE, 4, "I")
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_IOC_RD_MODE32 = _ioc_encode(_IOC_READ, 5, "I")
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_IOC_WR_MODE32 = _ioc_encode(_IOC_WRITE, 5, "I")
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# pylint: disable=too-many-arguments
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def __init__(
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self,
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device,
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max_speed_hz=None,
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bits_per_word=None,
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phase=None,
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polarity=None,
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cs_high=None,
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lsb_first=None,
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three_wire=None,
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loop=None,
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no_cs=None,
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ready=None,
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):
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"""
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Create spidev interface object.
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"""
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if isinstance(device, tuple):
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(bus, dev) = device
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device = f"/dev/spidev{bus:d}.{dev:d}"
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if not os.path.exists(device):
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raise IOError(f"{device} does not exist")
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self.handle = os.open(device, os.O_RDWR)
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self.chunk_size = SPI_DEFAULT_CHUNK_SIZE
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if environ.get("SPI_BUFSIZE") is not None:
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try:
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self.chunk_size = int(os.environ.get("SPI_BUFSIZE"))
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except ValueError:
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self.chunk_size = SPI_DEFAULT_CHUNK_SIZE
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if max_speed_hz is not None:
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self.max_speed_hz = max_speed_hz
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if bits_per_word is not None:
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self.bits_per_word = bits_per_word
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if phase is not None:
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self.phase = phase
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if polarity is not None:
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self.polarity = polarity
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if cs_high is not None:
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self.cs_high = cs_high
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if lsb_first is not None:
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self.lsb_first = lsb_first
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if three_wire is not None:
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self.three_wire = three_wire
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if loop is not None:
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self.loop = loop
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if no_cs is not None:
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self.no_cs = no_cs
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if ready is not None:
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self.ready = ready
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# pylint: enable=too-many-arguments
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def _ioctl(self, ioctl_data, data=None):
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"""
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ioctl helper function.
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Performs an ioctl on self.handle. If the ioctl is an SPI read type
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ioctl, returns the result value.
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"""
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(direction, ioctl_bytes, structure) = ioctl_data
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if direction == SPI._IOC_READ:
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arg = array.array(structure, [0])
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ioctl(self.handle, ioctl_bytes, arg, True)
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return arg[0]
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arg = struct.pack("=" + structure, data)
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ioctl(self.handle, ioctl_bytes, arg)
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return None
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def _get_mode_field(self, field):
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"""Helper function to get specific spidev mode bits"""
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return bool(self._ioctl(SPI._IOC_RD_MODE) & field)
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def _set_mode_field(self, field, value):
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"""Helper function to set a spidev mode bit"""
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mode = self._ioctl(SPI._IOC_RD_MODE)
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if value:
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mode |= field
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else:
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mode &= ~field
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self._ioctl(SPI._IOC_WR_MODE, mode)
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@property
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def phase(self):
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"""SPI clock phase bit"""
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return self._get_mode_field(SPI_CPHA)
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@phase.setter
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def phase(self, phase):
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self._set_mode_field(SPI_CPHA, phase)
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@property
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def polarity(self):
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"""SPI polarity bit"""
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return self._get_mode_field(SPI_CPOL)
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@polarity.setter
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def polarity(self, polarity):
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self._set_mode_field(SPI_CPOL, polarity)
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@property
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def cs_high(self):
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"""SPI chip select active level"""
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return self._get_mode_field(SPI_CS_HIGH)
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@cs_high.setter
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def cs_high(self, cs_high):
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self._set_mode_field(SPI_CS_HIGH, cs_high)
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@property
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def lsb_first(self):
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"""Bit order of SPI word transfers"""
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return self._get_mode_field(SPI_LSB_FIRST)
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@lsb_first.setter
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def lsb_first(self, lsb_first):
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self._set_mode_field(SPI_LSB_FIRST, lsb_first)
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@property
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def three_wire(self):
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"""SPI 3-wire mode"""
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return self._get_mode_field(SPI_THREE_WIRE)
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@three_wire.setter
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def three_wire(self, three_wire):
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self._set_mode_field(SPI_THREE_WIRE, three_wire)
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@property
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def loop(self):
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"""SPI loopback mode"""
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return self._get_mode_field(SPI_LOOP)
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@loop.setter
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def loop(self, loop):
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self._set_mode_field(SPI_LOOP, loop)
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@property
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def no_cs(self):
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"""No chipselect. Single device on bus."""
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return self._get_mode_field(SPI_NO_CS)
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@no_cs.setter
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def no_cs(self, no_cs):
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self._set_mode_field(SPI_NO_CS, no_cs)
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@property
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def ready(self):
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"""Slave pulls low to pause"""
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return self._get_mode_field(SPI_READY)
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@ready.setter
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def ready(self, ready):
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self._set_mode_field(SPI_READY, ready)
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@property
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def max_speed_hz(self):
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"""Maximum SPI transfer speed in Hz.
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Note that the controller cannot necessarily assign the requested
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speed.
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"""
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return self._ioctl(SPI._IOC_RD_MAX_SPEED_HZ)
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@max_speed_hz.setter
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def max_speed_hz(self, max_speed_hz):
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self._ioctl(SPI._IOC_WR_MAX_SPEED_HZ, max_speed_hz)
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@property
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def bits_per_word(self):
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"""Number of bits per word of SPI transfer.
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A value of 0 is equivalent to 8 bits per word
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"""
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return self._ioctl(SPI._IOC_RD_BITS_PER_WORD)
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@bits_per_word.setter
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def bits_per_word(self, bits_per_word):
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self._ioctl(SPI._IOC_WR_BITS_PER_WORD, bits_per_word)
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@property
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def mode(self):
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"""Mode that SPI is currently running in"""
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return self._ioctl(SPI._IOC_RD_MODE)
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@mode.setter
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def mode(self, mode):
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self._ioctl(SPI._IOC_WR_MODE, mode)
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def writebytes(self, data, max_speed_hz=0, bits_per_word=0, delay=0):
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"""Perform half-duplex SPI write."""
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data = array.array("B", data).tobytes()
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# length = len(data)
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chunks = [
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data[i : i + self.chunk_size] for i in range(0, len(data), self.chunk_size)
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]
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for chunk in chunks:
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length = len(chunk)
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transmit_buffer = create_string_buffer(chunk)
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spi_ioc_transfer = struct.pack(
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SPI._IOC_TRANSFER_FORMAT,
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addressof(transmit_buffer),
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0,
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length,
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max_speed_hz,
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delay,
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bits_per_word,
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0,
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0,
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0,
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0,
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)
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try:
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ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
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except TimeoutError as err:
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raise Exception( # pylint: disable=broad-exception-raised
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"ioctl timeout. Please try a different SPI frequency or less data."
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) from err
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def readbytes(self, length, max_speed_hz=0, bits_per_word=0, delay=0):
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"""Perform half-duplex SPI read as a binary string"""
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receive_buffer = create_string_buffer(length)
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spi_ioc_transfer = struct.pack(
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SPI._IOC_TRANSFER_FORMAT,
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0,
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addressof(receive_buffer),
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length,
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max_speed_hz,
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delay,
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bits_per_word,
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0,
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0,
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0,
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0,
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)
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ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
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return string_at(receive_buffer, length)
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def transfer(self, data, max_speed_hz=0, bits_per_word=0, delay=0):
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"""Perform full-duplex SPI transfer"""
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data = array.array("B", data).tobytes()
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receive_data = []
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chunks = [
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data[i : i + self.chunk_size] for i in range(0, len(data), self.chunk_size)
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]
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for chunk in chunks:
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length = len(chunk)
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receive_buffer = create_string_buffer(length)
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transmit_buffer = create_string_buffer(chunk)
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spi_ioc_transfer = struct.pack(
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SPI._IOC_TRANSFER_FORMAT,
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addressof(transmit_buffer),
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addressof(receive_buffer),
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length,
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max_speed_hz,
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delay,
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bits_per_word,
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0,
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0,
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0,
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0,
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)
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ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
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receive_data += string_at(receive_buffer, length)
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return receive_data
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