mirror of
https://github.com/KevinMidboe/python-gpiozero.git
synced 2025-10-29 17:50:37 +00:00
99 lines
3.3 KiB
Python
99 lines
3.3 KiB
Python
from __future__ import (
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unicode_literals,
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print_function,
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absolute_import,
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division,
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)
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str = type('')
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import operator
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from threading import RLock
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from ..devices import Device, SharedMixin
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from ..input_devices import InputDevice
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from ..output_devices import OutputDevice
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class SPISoftwareBus(SharedMixin, Device):
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def __init__(self, clock_pin, mosi_pin, miso_pin):
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self.lock = None
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self.clock = None
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self.mosi = None
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self.miso = None
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super(SPISoftwareBus, self).__init__()
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self.lock = RLock()
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try:
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self.clock = OutputDevice(clock_pin, active_high=True)
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if mosi_pin is not None:
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self.mosi = OutputDevice(mosi_pin)
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if miso_pin is not None:
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self.miso = InputDevice(miso_pin)
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except:
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self.close()
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raise
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def close(self):
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super(SPISoftwareBus, self).close()
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if self.lock:
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with self.lock:
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if self.miso is not None:
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self.miso.close()
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self.miso = None
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if self.mosi is not None:
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self.mosi.close()
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self.mosi = None
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if self.clock is not None:
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self.clock.close()
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self.clock = None
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self.lock = None
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@property
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def closed(self):
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return self.lock is None
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@classmethod
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def _shared_key(cls, clock_pin, mosi_pin, miso_pin):
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return (clock_pin, mosi_pin, miso_pin)
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def transfer(self, data, clock_phase=False, lsb_first=False, bits_per_word=8):
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"""
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Writes data (a list of integer words where each word is assumed to have
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:attr:`bits_per_word` bits or less) to the SPI interface, and reads an
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equivalent number of words, returning them as a list of integers.
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"""
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result = []
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with self.lock:
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# See https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus
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# (specifically the section "Example of bit-banging the master
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# protocol") for a simpler C implementation of this which ignores
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# clock polarity, phase, variable word-size, and multiple input
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# words
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if lsb_first:
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shift = operator.lshift
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init_mask = 1
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else:
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shift = operator.rshift
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init_mask = 1 << (bits_per_word - 1)
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for write_word in data:
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mask = init_mask
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read_word = 0
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for _ in range(bits_per_word):
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if self.mosi is not None:
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self.mosi.value = bool(write_word & mask)
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# read bit on clock activation
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self.clock.on()
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if not clock_phase:
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if self.miso is not None and self.miso.value:
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read_word |= mask
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# read bit on clock deactivation
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self.clock.off()
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if clock_phase:
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if self.miso is not None and self.miso.value:
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read_word |= mask
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mask = shift(mask, 1)
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result.append(read_word)
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return result
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