def setup_change_detect_callback(lines, callback, timer, names=None):
# Since the user may have specified a range of lines (e.g.,
# 'Dev1/port0/line0:1') or listed each line individually (e.g.,
# 'Dev1/port0/line0, Dev1/port0/line1'), we need to extract the individual
# lines in the task. This allows the callback helper to report the name of
# the line on which the event was detected.
lines = channel_list(lines, 'digital')
if names is not None:
if len(names) != len(lines):
raise ValueError('Number of names must match number of lines')
else:
names = lines
task = create_task()
line_string = ','.join(lines)
mx.DAQmxCreateDIChan(task, line_string, '', mx.DAQmx_Val_ChanForAllLines)
# Get the current state of the lines so that we know what happened during
# the first change detection event.
mx.DAQmxStartTask(task)
initial_state = read_digital_lines(task, 1)
mx.DAQmxStopTask(task)
# If we're using change detection timing on the digital lines, there's no
# point in reading them in as a hardware-timed buffered task. Given the
# event times, we can always reconstruct the state of the line at any given
# time.
mx.DAQmxCfgChangeDetectionTiming(task, line_string, line_string,
mx.DAQmx_Val_ContSamps, 200)
mx.DAQmxCfgInputBuffer(task, 0)
cb = ChangeDetectionCallbackHelper(names, callback, initial_state, timer)
cb_ptr = mx.DAQmxSignalEventCallbackPtr(cb)
mx.DAQmxRegisterSignalEvent(task, mx.DAQmx_Val_ChangeDetectionEvent, 0,
cb_ptr, None)
task._cb_ptr = cb_ptr
mx.DAQmxTaskControl(task, mx.DAQmx_Val_Task_Commit)
return task
