Source code for periphery.spi

import os
import fcntl
import array
import ctypes

[docs]class SPIError(IOError): """Base class for SPI errors.""" pass
class _CSpiIocTransfer(ctypes.Structure): _fields_ = [ ('tx_buf', ctypes.c_ulonglong), ('rx_buf', ctypes.c_ulonglong), ('len', ctypes.c_uint), ('speed_hz', ctypes.c_uint), ('delay_usecs', ctypes.c_ushort), ('bits_per_word', ctypes.c_ubyte), ('cs_change', ctypes.c_ubyte), ('tx_nbits', ctypes.c_ubyte), ('rx_nbits', ctypes.c_ubyte), ('pad', ctypes.c_ushort), ]
[docs]class SPI(object): # Constants scraped from <linux/spi/spidev.h> _SPI_CPHA = 0x1 _SPI_CPOL = 0x2 _SPI_LSB_FIRST = 0x8 _SPI_IOC_WR_MODE = 0x40016b01 _SPI_IOC_RD_MODE = 0x80016b01 _SPI_IOC_WR_MAX_SPEED_HZ = 0x40046b04 _SPI_IOC_RD_MAX_SPEED_HZ = 0x80046b04 _SPI_IOC_WR_BITS_PER_WORD = 0x40016b03 _SPI_IOC_RD_BITS_PER_WORD = 0x80016b03 _SPI_IOC_MESSAGE_1 = 0x40206b00 def __init__(self, devpath, mode, max_speed, bit_order="msb", bits_per_word=8, extra_flags=0): """Instantiate a SPI object and open the spidev device at the specified path with the specified SPI mode, max speed in hertz, and the defaults of "msb" bit order and 8 bits per word. Args: devpath (str): spidev device path. mode (int): SPI mode, can be 0, 1, 2, 3. max_speed (int, float): maximum speed in Hertz. bit_order (str): bit order, can be "msb" or "lsb". bits_per_word (int): bits per word. extra_flags (int): extra spidev flags to be bitwise-ORed with the SPI mode. Returns: SPI: SPI object. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `devpath`, `mode`, `max_speed`, `bit_order`, `bits_per_word`, or `extra_flags` types are invalid. ValueError: if `mode`, `bit_order`, `bits_per_word`, or `extra_flags` values are invalid. """ self._fd = None self._devpath = None self._open(devpath, mode, max_speed, bit_order, bits_per_word, extra_flags) def __del__(self): self.close() def __enter__(self): pass def __exit__(self, t, value, traceback): self.close() def _open(self, devpath, mode, max_speed, bit_order, bits_per_word, extra_flags): if not isinstance(devpath, str): raise TypeError("Invalid devpath type, should be string.") elif not isinstance(mode, int): raise TypeError("Invalid mode type, should be integer.") elif not isinstance(max_speed, (int, float)): raise TypeError("Invalid max_speed type, should be integer or float.") elif not isinstance(bit_order, str): raise TypeError("Invalid bit_order type, should be string.") elif not isinstance(bits_per_word, int): raise TypeError("Invalid bits_per_word type, should be integer.") elif not isinstance(extra_flags, int): raise TypeError("Invalid extra_flags type, should be integer.") if mode not in [0, 1, 2, 3]: raise ValueError("Invalid mode, can be 0, 1, 2, 3.") elif bit_order.lower() not in ["msb", "lsb"]: raise ValueError("Invalid bit_order, can be \"msb\" or \"lsb\".") elif bits_per_word < 0 or bits_per_word > 255: raise ValueError("Invalid bits_per_word, must be 0-255.") elif extra_flags < 0 or extra_flags > 255: raise ValueError("Invalid extra_flags, must be 0-255.") # Open spidev try: self._fd = os.open(devpath, os.O_RDWR) except OSError as e: raise SPIError(e.errno, "Opening SPI device: " + e.strerror) self._devpath = devpath bit_order = bit_order.lower() # Set mode, bit order, extra flags buf = array.array("B", [mode | (SPI._SPI_LSB_FIRST if bit_order == "lsb" else 0) | extra_flags]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MODE, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI mode: " + e.strerror) # Set max speed buf = array.array("I", [int(max_speed)]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MAX_SPEED_HZ, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI max speed: " + e.strerror) # Set bits per word buf = array.array("B", [bits_per_word]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_BITS_PER_WORD, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI bits per word: " + e.strerror) # Methods
[docs] def transfer(self, data): """Shift out `data` and return shifted in data. Args: data (bytes, bytearray, list): a byte array or list of 8-bit integers to shift out. Returns: bytes, bytearray, list: data shifted in. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `data` type is invalid. ValueError: if data is not valid bytes. """ if not isinstance(data, (bytes, bytearray, list)): raise TypeError("Invalid data type, should be bytes, bytearray, or list.") # Create mutable array try: buf = array.array('B', data) except OverflowError: raise ValueError("Invalid data bytes.") buf_addr, buf_len = buf.buffer_info() # Prepare transfer structure spi_xfer = _CSpiIocTransfer() spi_xfer.tx_buf = buf_addr spi_xfer.rx_buf = buf_addr spi_xfer.len = buf_len # Transfer try: fcntl.ioctl(self._fd, SPI._SPI_IOC_MESSAGE_1, spi_xfer) except OSError as e: raise SPIError(e.errno, "SPI transfer: " + e.strerror) # Return shifted out data with the same type as shifted in data if isinstance(data, bytes): return bytes(bytearray(buf)) elif isinstance(data, bytearray): return bytearray(buf) elif isinstance(data, list): return buf.tolist()
[docs] def close(self): """Close the spidev SPI device. Raises: SPIError: if an I/O or OS error occurs. """ if self._fd is None: return try: os.close(self._fd) except OSError as e: raise SPIError(e.errno, "Closing SPI device: " + e.strerror) self._fd = None
# Immutable properties @property def fd(self): """Get the file descriptor of the underlying spidev device. :type: int """ return self._fd @property def devpath(self): """Get the device path of the underlying spidev device. :type: str """ return self._devpath # Mutable properties def _get_mode(self): buf = array.array('B', [0]) # Get mode try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) return buf[0] & 0x3 def _set_mode(self, mode): if not isinstance(mode, int): raise TypeError("Invalid mode type, should be integer.") if mode not in [0, 1, 2, 3]: raise ValueError("Invalid mode, can be 0, 1, 2, 3.") # Read-modify-write mode, because the mode contains bits for other settings # Get mode buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) buf[0] = (buf[0] & ~(SPI._SPI_CPOL | SPI._SPI_CPHA)) | mode # Set mode try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MODE, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI mode: " + e.strerror) mode = property(_get_mode, _set_mode) """Get or set the SPI mode. Can be 0, 1, 2, 3. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `mode` type is not int. ValueError: if `mode` value is invalid. :type: int """ def _get_max_speed(self): # Get max speed buf = array.array('I', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MAX_SPEED_HZ, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI max speed: " + e.strerror) return buf[0] def _set_max_speed(self, max_speed): if not isinstance(max_speed, (int, float)): raise TypeError("Invalid max_speed type, should be integer or float.") # Set max speed buf = array.array('I', [int(max_speed)]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MAX_SPEED_HZ, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI max speed: " + e.strerror) max_speed = property(_get_max_speed, _set_max_speed) """Get or set the maximum speed in Hertz. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `max_speed` type is not int or float. :type: int, float """ def _get_bit_order(self): # Get mode buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) if (buf[0] & SPI._SPI_LSB_FIRST) > 0: return "lsb" return "msb" def _set_bit_order(self, bit_order): if not isinstance(bit_order, str): raise TypeError("Invalid bit_order type, should be string.") elif bit_order.lower() not in ["msb", "lsb"]: raise ValueError("Invalid bit_order, can be \"msb\" or \"lsb\".") # Read-modify-write mode, because the mode contains bits for other settings # Get mode buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) bit_order = bit_order.lower() buf[0] = (buf[0] & ~SPI._SPI_LSB_FIRST) | (SPI._SPI_LSB_FIRST if bit_order == "lsb" else 0) # Set mode try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MODE, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI mode: " + e.strerror) bit_order = property(_get_bit_order, _set_bit_order) """Get or set the SPI bit order. Can be "msb" or "lsb". Raises: SPIError: if an I/O or OS error occurs. TypeError: if `bit_order` type is not str. ValueError: if `bit_order` value is invalid. :type: str """ def _get_bits_per_word(self): # Get bits per word buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_BITS_PER_WORD, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI bits per word: " + e.strerror) return buf[0] def _set_bits_per_word(self, bits_per_word): if not isinstance(bits_per_word, int): raise TypeError("Invalid bits_per_word type, should be integer.") if bits_per_word < 0 or bits_per_word > 255: raise ValueError("Invalid bits_per_word, must be 0-255.") # Set bits per word buf = array.array('B', [bits_per_word]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_BITS_PER_WORD, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI bits per word: " + e.strerror) bits_per_word = property(_get_bits_per_word, _set_bits_per_word) """Get or set the SPI bits per word. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `bits_per_word` type is not int. ValueError: if `bits_per_word` value is invalid. :type: int """ def _get_extra_flags(self): # Get mode buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) return buf[0] & ~(SPI._SPI_LSB_FIRST | SPI._SPI_CPHA | SPI._SPI_CPOL) def _set_extra_flags(self, extra_flags): if not isinstance(extra_flags, int): raise TypeError("Invalid extra_flags type, should be integer.") if extra_flags < 0 or extra_flags > 255: raise ValueError("Invalid extra_flags, must be 0-255.") # Read-modify-write mode, because the mode contains bits for other settings # Get mode buf = array.array('B', [0]) try: fcntl.ioctl(self._fd, SPI._SPI_IOC_RD_MODE, buf, True) except OSError as e: raise SPIError(e.errno, "Getting SPI mode: " + e.strerror) buf[0] = (buf[0] & (SPI._SPI_LSB_FIRST | SPI._SPI_CPHA | SPI._SPI_CPOL)) | extra_flags # Set mode try: fcntl.ioctl(self._fd, SPI._SPI_IOC_WR_MODE, buf, False) except OSError as e: raise SPIError(e.errno, "Setting SPI mode: " + e.strerror) extra_flags = property(_get_extra_flags, _set_extra_flags) """Get or set the spidev extra flags. Extra flags are bitwise-ORed with the SPI mode. Raises: SPIError: if an I/O or OS error occurs. TypeError: if `extra_flags` type is not int. ValueError: if `extra_flags` value is invalid. :type: int """ # String representation def __str__(self): return "SPI (device=%s, fd=%d, mode=%s, max_speed=%d, bit_order=%s, bits_per_word=%d, extra_flags=0x%02x)" % (self.devpath, self.fd, self.mode, self.max_speed, self.bit_order, self.bits_per_word, self.extra_flags)