Aded support for read properties: read_relative_to, read_overwrite, offset,

Hi there,

I've created a patch to implement the following ni-DAQmx read property calls:

DAQmxGetReadRelativeTo() --> task.get_read_relative_to()
DAQmxSetReadRelativeTo() --> task.set_read_relative_to()
DAQmxResetReadRelativeTo() --> task.reset_read_relative_to()

DAQmxGetReadOverwrite() --> task.get_read_overwrite()
DAQmxSetReadOverwrite() --> task.set_read_overwrite()
DAQmxResetReadOverwrite() --> task.reset_read_overwrite()

DAQmxGetReadOffset() --> task.get_read_offset()
DAQmxSetReadOffset() --> task.set_read_offset()
DAQmxResetReadOffset() --> task.reset_read_offset()

These are useful when making measurements where only the last last x samples in 
the buffer are required.  Setting these properties and the clock to continuous 
acquisition can also decrease the time required to start and stop the task if 
you make frequent, repeated measurements.  An example of usage is below:

>>> from nidaqmx import AnalogInputTask
>>> task = AnalogInputTask()
>>> task.create_voltage_channel('Dev1/ai0', terminal='diff', min_val=0., 
max_val=5.)
>>> task.configure_timing_sample_clock(rate=2e6, sample_mode='continuous', 
samples_per_channel=32000)
>>> task.set_read_relative_to('most_recent')
>>> task.set_read_overwrite('overwrite')
>>> task.set_read_offset(32000)
>>> task.start()
>>> task.read(32000)
array([[ 2.99478992],
       [ 2.9951122 ],
       [ 2.99478992],
       ...,
       [ 2.99462878],
       [ 2.9951122 ],
       [ 2.99462878]])
>>> task.read(32000)
array([[ 2.99462878],
       [ 2.99446764],
       [ 2.99462878],
       ...,
       [ 2.99478992],
       [ 2.99495106],
       [ 2.9951122 ]])

etc.

Tested with nidaqmx v. 9.5 and a USB-6363 DAQ box.  The docstrings might be a 
little verbose, so feel free to cut them down if you think it's appropriate (I 
based them off of the C API documentation).

Thanks,
toki

Original issue reported on code.google.com by reddoghud on 12 Sep 2012 at 12:13

Attachments:

libnidaqmx.py.patch

pearu / pylibnidaqmx

Aded support for read properties: read_relative_to, read_overwrite, offset, #31