ZMQ Serial driver

[simbilod]

New driver class for serial connections that occur through an intermediate server, for instance

User <--> Client (e.g. instrumentation server) <--ZMQ--> Server/controller (e.g. Raspberry PI) <--Serial/USB--> Instrument

There is also an example of a driver leveraging this (MDT693B, Thorlabs Piezo Controller)

As described in the example notebook, the user experience is setup to be identical to other lightlab drivers. The user only needs to connect the server/controller machine to the instrument, and setup passwordless SSH access from the client machine to it. Then, for the user it is as if the instrument is directly connected to the client, with simple execution such as

    stage = MDT693B_OLPC(name='stage', server_address='IP_address', server_user='pi')
    print(stage.set_volt('x', 12)) # outputs 1 for successful upload
    print(stage.get_volt('x')) # outputs 12

This is enabled by the fact that, when instanciating an instrument subclassed from this driver type, ZMQ server code is automatically uploaded and then persistently executed on the server/controller. The client can then use ZMQclient methods such as request and write to send commands to the instrument, relayed through the server/controller. The user can then entirely focus on adapting the serial commands from the instrument manual:

def get_volt(self, axis):
    cmd = "{}voltage?".format(axis)
    ans = self.request(cmd)
    return float(ans.strip('[]\r> '))

TODO:

• Allow non-passwordless connections between client and server/controller. Since there is only one SSH connection during instanciation, it would be nice to have the option to just provide a password once there (like Paramiko allows).
• Add hardware-free unit test, maybe spawing client/server on localhost with a dummy instrument.
• Add better logging, need to decide what to do about server vs client logging, since user presumably only
• Support for multiple commands on the same communication

[simbilod]

@thomaslima @jclederman just wondering if you have some comments before I merge to development

[jclederman]

I think this makes sense. What happens if two Piezo controllers are connected to the same pi? Is there a way of specifying some local USB address (like the GPIB address)? I'm picturing something similar to the prologix, where there is a pi prefix, the ip address, then the local address

[simbilod]

Yes sorry should have linked the notebook. Look at the function call for the driver/ZMQclient here

[atait]

+1 for decentralization! This will be useful. Could you put some things in the automated test? It could be very simple like launching a server process, then pinging it at "localhost". @simbilod I have just shared some code to your email with similar examples.

[simbilod]

@jclederman in your example you would spin two servers on two different zmq_ports, each with the required serial_port

@atait yes I was thinking about that (it's on the TODO). Thanks for the example. I will add this before I merge.