artiq/artiq/coredevice/pcf8574a.py

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from artiq.experiment import kernel
from artiq.coredevice.i2c import (
i2c_start, i2c_write, i2c_read, i2c_stop, I2CError)
class PCF8574A:
"""Driver for the PCF8574 I2C remote 8-bit I/O expander.
I2C transactions not real-time, and are performed by the CPU without
involving RTIO.
"""
def __init__(self, dmgr, busno=0, address=0x7c, core_device="core"):
self.core = dmgr.get(core_device)
self.busno = busno
self.address = address
@kernel
def set(self, data):
"""Drive data on the quasi-bidirectional pins.
:param data: Pin data. High bits are weakly driven high
(and thus inputs), low bits are strongly driven low.
"""
i2c_start(self.busno)
try:
if not i2c_write(self.busno, self.address):
raise I2CError("PCF8574A failed to ack address")
if not i2c_write(self.busno, data):
raise I2CError("PCF8574A failed to ack data")
finally:
i2c_stop(self.busno)
@kernel
def get(self):
"""Retrieve quasi-bidirectional pin input data.
:return: Pin data
"""
i2c_start(self.busno)
ret = 0
try:
if not i2c_write(self.busno, self.address | 1):
raise I2CError("PCF8574A failed to ack address")
ret = i2c_read(self.busno, False)
finally:
i2c_stop(self.busno)
return ret