Scope binary parsing problem

[brooksfoxen]

I finally tracked my scope issue down to bad parsing of the binary waveform data. There is a function 'query_binary_values" built in to the VISA driver that queries data and parses it correctly.

I've added this function call to the gpib_server.py file and I have successfully tested this fix with the scope accessing this function directly through the gpib_bus:
'''
cxn = labrad.connect()
scope = cxn.collateral_gpib_bus
scope.address(scope.list_devices()[-1])
scope.query_binary_values(':WAVeform:SOURce CHANnel4;DATA?', "h", True)
'''

However, when I went to implement this query in the agilent_infiniium_scope server, it doesn't seem to know about the new query_binary_values function. Is there some other class definition or something I need to update to add this query_binary_values function to the agilent_infiniium_scope server?

@maffoo

[brooksfoxen]

I think I found what I need to change in pylabrad @thchwhite helped me out. I'm going to do that and I'll submit pull requests when I get it working.

[brooksfoxen]

gpib_server.py change:
https://github.com/martinisgroup/servers/tree/u/Brooks/issue%23356
https://github.com/labrad/pylabrad/tree/u/Brooks/issue%23356

[maffoo]

We tracked this down to the fact that the gpib server tries to strip trailing termination characters like \r and \n (https://github.com/martinisgroup/servers/blob/master/gpib_server.py#L183). This does not work if trying to read binary data, since trailing bytes that just happen to correspond to these termination characters can be dropped. I think the solution to this is to add a separate read_raw setting to be used for reading raw bytes, versus the read setting that reads string responses. This mirrors the underlying pyvisa interface as well (https://github.com/hgrecco/pyvisa/blob/master/pyvisa/resources/messagebased.py#L288).

Note also labrad/pylabrad#268 which describes a way to hopefully make it easier to fix problems in the gpib system by keeping the bus and device manager servers close to the gpib device server code.