Driver Programming

Drivers are small Python-based code snippets that define how SweepMe! should interact with different instruments. Driver programming in SweepMe! refers to the process of creating new drivers or enhancing the capabilities of existing ones to expand or customize the functionalities of SweepMe! measurement procedures. The drivers are open-source and can be found on the instrument-drivers GitHub repository.

Core Principles

Conceptualization of Instruments

SweepMe! abstracts physical instruments into functional units, focusing on the features needed for specific tasks. This approach simplifies user interaction with the software and enhances its versatility. For example, a multifunction device can be divided into separate drivers for each of its capabilities, such as signal generation and signal measurement, allowing users to access and control different functionalities independently.

The EmptyDevice Class

The foundation of driver programming in SweepMe! is the EmptyDevice class. This class outlines the basic structure and sequence of operations required for a device to function within the software. It includes methods such as connect, initialize, and measure, into which developers insert the specific Python commands needed to control their hardware. The Sequencer procedure then dictates the order in which these methods are called by SweepMe!, ensuring a smooth workflow.

Example Driver

The following pseudo-code is an example of how a driver for a generic voltmeter could look like:

from pysweepme.EmptyDeviceClass import EmptyDevice  # Loading the EmptyDevice Class

class Device(EmptyDevice):             # Creating a new Device Class by inheriting from EmptyDevice
    def __init__(self):                # The python class object need to be initialized
        super().__init__()             # Initialize the parent class EmptyDevice
       
        self.variables = ["Voltage"]   # Define which parameters are measured 
        self.units = ["V"]            

    def connect(self):
        self.voltmeter = connect_to_voltmeter()  # Use existing Python libraries or communicate directly

    def configure(self):
        self.voltmeter.set_unit("volt")          # Set the device parameter

    def measure(self):
        self.data = self.voltmeter.read_values() # Retrieve data from device

    def call(self):
        return self.data               # return measured data to SweepMe!

All Drivers that are available via the version manager are also examples. Download them and see the source code, e.g. using the "Open/Modify" button that each module has. Copy Drivers to the public folder "CustomDevices" using the version manager and start using them as a template for your own Drivers.

Step-by-Step Guide

Choosing Your Starting Point

There are three paths you can take to start developing your driver:

• Leverage Existing Drivers: Begin by finding a driver in the Version manager that closely matches your device's functionality. Create a custom version and rename it. This approach gives you a solid foundation to modify and adapt the driver to your specific needs.
• Use the Device Class Template: For a more structured start, use the Device Class Template. It's a blueprint that guides you through the essential components of a driver.

• Start from Scratch: Advanced users might prefer starting with an empty Python file, building the driver from the ground up.

Development Steps

1. Import Modules: Begin by importing the necessary Python modules for your driver.
2. Create the Device Class: Follow the example to define your Device class. This class is where you'll implement the functionality of your driver.
3. Define Static Variables: Add static variables such as "description" to provide information about your driver.
4. Initialization Functions:
   1. Implement the __init__ function for initializing your class and define return variables.
   2. If your device requires port discovery, add the find_Ports function or use the Port manager.
   3. Include set_GUIparameter and get_GUIparameter to interact with the GUI elements.
5. Implement Standard Functions: Add functions like connect, disconnect, initialize, deinitialize, configure, unconfigure, signin, and signout. Group these functions together for clarity.
6. Measurement Point Functions: Incorporate standard functions called at each measurement point, such as start, apply, measure, and call. Maintain the sequence to ensure logical flow.
7. Optional: Setter and Getter Functions: Create functions to simplify access to the instrument's properties (e.g., set_voltage, get_voltage). These can be used within standard semantic functions or when Drivers are used in independent python programs, e.g. using pysweepme.
8. Convenience Functions: At the end, add any helper functions that facilitate driver programming but don't directly interact with device properties.

Programming style guide

All points are recommendations that might help you to create a Driver but feel free to do it your way. Also, rudimentary Drivers that do not support all features of an instrument or a certain programming style can be very helpful to other users to get started.

• A Driver should be as convenient as possible. If you can make a decision for the user by doing some extra checks or by getting the information from a config file try to include it.

• If a user could enter values that are not supported by the instrument, use the function initialize to do an initial check and stop the measurement if a value is not supported. Inform the user what was wrong and which values are supported.

• Whenever you get a value e.g. "self.value" during apply or any parameter during "get_GUIparameter" transform them immediately into the type you need. The type of a parameter can change (e.g. from integer to string) at some point, when a value is handed over from a different module or if the user interface of a module is changed in the future. By redefining the type of the parameter, you can ensure that your Driver will not break.

• Sometimes the user interface of a module does not support all options of your instrument. In that case, contact us to discuss how we can improve the module. Sometimes it is also possible to 'stretch' the user interface to your needs. For example: A module has the option "Input" (represented by a drop-down menu), but your instrument has two inputs that can be selected/deselected, then you can add possible choices like "None", "1", "2", and "1 & 2". That way, you do not need a second user interface option like "Input 2" to support the second input.

• Variables should start with capital letters and use no underscore or camel case programming style. Whitespaces are possible.

• GUi parameters that are created using set_GUIparameter in modules Logger, Switch, or Robot should start with a capital letter, can use white spaces, and should be user-friendly (e.g. no underscore, no camel case)

• pysweepme examples should be in the folder "pysweepme" that is in the driver folder.

Initialization

Importing Python packages

All packages that come along with SweepMe! can be imported as usual at the beginning of the file. If you need to import packages that do not come with the SweepMe! installation, you can use the LibraryBuilder to ship an extra python package with your DeviceClass.

__init__

This function must be part of any Driver, and according to the minimal working example the function "__init__" of the base class "EmptyDevice" must be called first. Then, you can define variables, units, plottype, and savetype as described above. Furthermore, you can set the variable self.shortname to a string that will be shown in the sequencer to help the user to identify which instrument is used quickly. Besides that, you can use the __init__ function to define important variables that are frequently needed in all other functions.

Instantiation & destruction

An instance of the Driver is instantiated and destroyed very often:

• for each measurement run
• whenever the Module needs to know the 'variables', 'units', or the shortname

Thus, the __init__ should be a lightweight function as it is called often. It also means that you cannot store parameters in a Driver to use them later again. Every parameter of the Driver instance exists only as long as the Driver lives and after a run, for example, the Driver instance is destroyed. This further means that dll files or other files should not be loaded in the __init__ function, but rather during connect or initialize.

To handover parameters and objects to future Driver instances, use the functions 'store_parameter' and 'restore_parameter' as explained here.

Defining return variables

Each Driver can return an arbitrary number of variables that are subsequently available for plotting, displaying them in a monitor widget, or saving them to the measurement data file.

In the function "__init__" or in "get_GUIparameter" of your Driver you have to define the following objects:

self.variables = ["Variable1", "Variable2", "Variable3"]
self.units = ["s", "m", ""]

In this example, three variables are defined, but you can also add more. Please make sure that you have the same number of units which are defined as seconds, meters, and no unit (empty string).

self.plottype = [True, True, False]
self.savetype = [True, False, False]

Additionally, you can define 'self.plottype' and 'self.savetype' which again need to have the same length as 'self.variables'. If you do not define them, they will be always True for each variable. If the plottype of a variable is True, you can select this variable in the plot. If the savetype of a variable is True, the data of this variable is saved to the measurement file.

To return your measured data to SweepMe! use the call function and return as many values as you have defined variables.

Returned data types can be: int, float, str, bool, list, np.array

Ports

If you use standardized communications interfaces like GPIB, COM, or USBTMC, you make use of SweepMe!'s port manager that manages everything and you can use the write and read function to communicate with your instrument. Otherwise, you have to handle the creation and destruction of a port object yourself using the functions connect and disconnect.

Finding & selecting ports

If your Driver makes use of the port manager, available ports will be automatically added to the field "Port". Otherwise, you can add the function "find_Ports" and return a list of strings that identify possible ports. In both cases, you can retrieve the port selected by the user via the function "get_GUIparameter" using the key "Port".

Starting from SweepMe! 1.5.5, you can use the function "find_ports" which is recommended.

Multichannel Support

Some measurement equipment has two or more channels but only one communications port, e.g. some Source-Measuring-Units or Parameter Analyzers have multiple channels to independently source voltages or currents, but everything is controlled via one port. Use the key "Channel" with the functions "set_GUIparameter" and "get_GUIparameter" to list available ports in a Drop-down box.

GUI interaction

The interaction with the graphical user interface (GUI) is realized with the two functions get_GUIparameter and set_GUIparameter. The function get_GUIparameter receives a dictionary with all parameters of the GUI. The function set_GUIparameter has to return a dictionary that tells SweepMe! which GUI elements should be enabled (active) and which options or default values should be displayed.

Getting GUI parameter

To figure out which parameters are selected by the user, the function 'get_GUIparameter' has to be used. It has one argument 'parameter' that is used to hand over a dictionary that consists of keys that are related to the GUI elements of the Module and the selected values. Overwrite this function in your Driver to make use of it. For example:

def get_GUIparameter(self, parameter):
    print(parameter)

Here, the print command can be used to see the dictionary in the debug widget and learn which keys are accessible. These keys of the dictionary can vary between each Module, but there are some which are common for all, like "Label", "Device", "Port".

To load a single parameter, for example, the Sweep mode or the selected port, use:

def get_GUIparameter(self, parameter):
    self.sweepmode = str(parameter["SweepMode"])
    self.port_string = str(parameter["Port"])

The variables 'self.sweepmode' and 'self.port_string' contain 'self.' which makes them an attribute of the entire Driver so that you can use them in all other functions of your Drivers that have 'self' as the first argument.

It is good practice to immediately change the data type to whatever you need for further processing. Should, the type of data, that is handed over, change, your code will not break.

Typical functions:

• int(): change to an integer number
• float(): change to a float number
• str(): change to a string

Attention: Do not overwrite the parameters within the dictionary that was handed over in get_GUIparameter as this dictionary is still a global object and changes can influence the program behavior. This will be fixed with the release of 1.5.5.

Setting GUI parameter

GUI elements of the Module for which you implement your Driver must be activated. For that reason, put the following function into your DeviceClass

def set_GUIparameter(self):
    GUIparameter = {}
    return GUIparameter

Now, you can fill the dictionary GUIparameter with keys and values. Each key represents a certain GUI item of the Module.

GUIparameter = {
                "SweepMode" : ["Current in A", "Voltage in V"],  # define a list 
               }

Here, "SweepMode" represents the ComboBox of the Module that presents the possible modes to vary set values. To get all possible keys that can be used with set_GUIparameter, you can use the function get_GUIparameter.

For modules with a fixed user interface, you cannot change the type of the widget that is used for the given key. Accordingly, you have to use a certain format to set the value for a key, for example:

GUIparameter = {
                "KeyInteger"    : 1,                       # use an integer for a field that requires an integer such as a SpinBox
                "KeyFloat"      : 1.23,                    # use a float for a field that requires an float such as DoubleSpinBox
                "KeyString "    : "SomeText",              # use a string for a field that requires a string such as a LineEdit
                "KeyComboBox"   : ["Choice1", "Choice2"],  # use a list of strings for a field that requires a selection such as a ComboBox
                "KeyCheckBox"   : True,                    # use a bool for a field that requires a check such as a CheckBox
               }

Creating individual parameters

The Modules Logger, Switch, and Robot provide the possibility to generate GUI items dynamically. Just add your own keys to the dictionary and based on the type of the default value, the corresponding GUI element will be created for you.

GUIparameter = {
                "MyOwnKeyForInteger"   : 1,                       # define a GUI element to enter an integer
                "MyOwnKeyForFloat"     : 1.23,                    # define a GUI element to enter a float
                "MyOwnKeyForString"    : "SomeText",              # define a GUI element to enter a string
                "MyOwnKeyForSelection" : ["Choice1", "Choice2"],  # define a GUI element to select from a ComboBox
                "MyOwnKeyForBool"      : True,                    # define a GUI element to use CheckBox
                "MyOwnKeyForSeparator" : None,                    # define a GUI element that just displays the key with bold font
                ""                     : None,                    # an empty line
                "MyOwnKeyForFolder"    : pathlib.Path(<folder>),  # define a GUI element that displays a button to select a folder
                "MyOwnKeyForFile"      : pathlib.Path(<file>),    # define a GUI element that displays a button to select a file
                " "                    : None,                    # another empty line with a different key from the first empty line
               }

The keys you use will be returned then by get_GUIparameter with the selected values of the user. Please make sure that you do not use keys that are provided by the Module. See the description of get_GUIparameter to see which keys already exist.

Pre-defined GUI keys

Some keys should not be used to define your own GUI keys when creating Drivers for Logger, Switch, and Robot.

• "Label": The field where the user can change the label of the module
• "Device": The field where the user selects the Driver
• "Port": the field where the user selects the port
• "Calibration": the field where the user selects the calibration
• "Channel": the field where the user selects the channel
• "Description": the field where the user can read info about the Driver
• "SweepMode": the field where the user selects the sweep mode
• "SweepValue": the field where the user selects the sweep value

Parameter variation

It's oftentimes the case that the user wants to vary a parameter over the driver instrument and acquire data. In SweepMe!, parameters can be varied by two approaches, which is explained below.

Sweep

The main approach to do a parameter variation is through sweep. In a SweepMe! driver, the developer can define different parameter variations in a list in the GUIparameter dictionary with the key "SweepMode" under set_GUIparameter() method (See Setting GUI parameter and Getting GUI parameter sections). The "Sweep Mode" value can be used in other methods to configure the instrument. In addition to "Sweep Mode", there is a built-in "Sweep Value" GUI combobox element, where the user can select the source of the sweep from SweepMe!'s parameter space. This source value can be retrieved as self.value within the driver. Whenever the source value is changed, the apply() method of the driver will be called by SweepMe!.

Reconfigure

For module types like Logger, Switch, or Robot, the alternative approach to varying a parameter is to pass the parameter as a string with the following structure: {ModuleName_VariableName_Unit}. A list of all parameters can be found under the Parameters widget. For each parameter, the string can be simply copied by right-clicking on the parameter. Normally, SweepMe! takes the value of parameters only once at the beginning of the measurement. When a value of a parameter changes, however, this updated parameter and its value will be available within the method reconfigure(), as shown below:

def reconfigure(self, parameters, keys):
        print(keys) # A list of updated parameters
        print(parameters) # A dictionary of all parameters
        if "ParameterKey" in keys:
            updated_value = parameters["ParameterKey"]
            print(updated_value)

Please note that at the beginning of the measurement, the reconfigure method is called within signin(), i.e. before configure() and the parameter has its default value in all methods except reconfigure.

Parameter store

(available from SweepMe! 1.5.5)

The parameter store can be used to exchange parameters or objects between Driver instances during an entire SweepMe! session.

As Drivers are often instantiated and destroyed, it might be necessary to forward parameters or information to the next Driver instance during a SweepMe! session. There are two possibilities:

• parameters are stored in a configuration file
• parameters and stored in a parameter store that is provided by SweepMe!

To store a parameter, use

self.store_parameter(key, value)

where 'key' is a string and 'value' can be any Python object. The key-value pair is stored in a dictionary that is available to all Drivers and which exists during the entire SweepMe! session.

To restore a parameter, use

value = self.restore_parameter(key)

where 'key' is a string that was previously used during 'store_parameter' and 'value' is the object that was stored. If the key is unknown, 'None' is returned.

To erase a parameter, just set it back to None

self.store_parameter(key, None)

Communication between driver instances

Sometimes multiple instances of a driver are created for a measurement and they need to share some information, e.g. a certain object to handle the communication. For this purpose, a dictionary called "self.device_communication" is available in all drivers being the same in all driver instances. This dictionary is always emptied right at the start of a run. You can simply add a key-value pair and all other drivers can access the entries as well and vice versa. The dictionary is available starting with a measurement and can be accessed during all functions that are called during the measurement. To avoid interference, we recommend using very unique key-strings that e.g. include the name of the drivers or even the port identifier to differentiate between multiple units of the same instrument. For example, a Driver that opens a dll-file to communicate with a spectrometer will have exclusive access to that port. To allow multiple spectrometer modules and their drivers to access the same port object it must be made available to all.

def connect(self):
    
    if "my_spectrometer_port" in self.device_communication:           
        # it means that another instance of this device class already opened the port object
        self.port = self.device_communication["my_spectrometer_port"]   
    else:                                                             
        # the port object is not available yet, so we have to create it and make it available to other instances of the same device class
        self.port = create_some_port_object()
        self.device_communication["my_spectrometer_port"] = self.port

The same can be done when disconnecting and closing the port object:

def disconnect(self):
    
    if "my_spectrometer_port" in self.device_communication:
        # if the key is still available, the first instance of the Driver will close the port and remove the key
        self.port.close() # close your port or disconnect
        del self.device_communication["my_spectrometer_port"] # remove the key-value pair from the dictionary

Here, is important that that port is only closed once but not for all modules that access the same instrument. Once the key is removed from self.device_communication, further driver instances will not try to close the port object anymore.

The dictionary "self.device_communication" is emptied before each measurement so that values are not available during the next measurement.

Error Handling

Stop a measurement

The measurement stops whenever a standard function such as 'connect', 'initialize', ..., raises an exception. This can be used if you would like to abort the measurement whenever something goes wrong.

msg = "text-to-be-displayed-in-a-message-box-to-inform-user"
raise Exception(msg)

The error message will be displayed in a message box to the user.

Communication with the user

If you like to display a message in the info box of the "Measurement" tab, you can use:

self.message_Info("text-to-be-displayed-in-the-info-box")

If you like to inform the user with a message box, use

self.message_Box("text-to-be-displayed-in-the-message-box")

Please note that the message box is non-blocking and the measurement will continue, even if the the message is not confirmed by the user.

Log messages to a file

You can easily write messages to a file using

self.write_Log("message-to-be-saved")

The message will be saved in the file temp_logbook.txt within the temp-folder. When saving data the leading "temp" of the file will be automatically renamed by the given file name.

Find and get folders

Often you need to access some of the standard pre-defined folders. For that purpose, you can use the function 'get_Folder' that each Driver can use.

self.get_Folder("<KEY>") # returns an absolute path to the folder for a given <KEY>.

Starting from SweepMe! 1.5.5, you can use 'get_folder', which is recommended:

self.get_folder("<KEY>") # returns an absolute path to the folder for a given <KEY>.

Often used keys

• "SELF": the folder of the Driver script "main.py" (introduced with SweepMe! 1.5.5. -> please update to 1.5.5.44 or later because of a bug)
• "TEMP": the temporary folder in which all measurement data is stored before the user saves it
• "CUSTOMFILES" (>= 1.5.5) or "CUSTOM" (1.5.4): the folder "CustomFiles" of the public SweepMe! folder in which setup-specific files might be stored
• "EXTLIBS": the folder "ExternalLibraries" of the public SweepMe! folder in which external dll files can be stored
• "CALIBRATIONS": the folder "Calibrations" of the public SweepMe! folder in which calibrations files can be stored
• "PUBLIC": the public SweepMe! folder

Documentation

If a user of your Driver needs further instruction, we recommend uploading the driver to our server and adding a description on the webpage each driver gets on this webpage: [[1]]

If your Driver is not publicly available, add a descriptive comment to the code of the main.py file. In case you develop a Driver for the generic modules Logger and Switch, you can add a description to the Driver by inserting a text for the static variable 'description'

In general, we recommend to rather add more comments than less. It will help other users understand the code and to learn developing own drivers.

Description

Drivers that are programmed for the modules Logger, Switch, or Robot can have a description that is displayed in the description box when the corresponding Driver is selected.

To enable this feature, add a static variable 'description' to your class, e.g.

class Device(EmptyDevice):
    description = "here you describe how your Driver should be used" # a static variable

    def __init__(self):
       ...

The string will be interpreted like HTML, so that headings, enumerations, etc. are possible.

Module-specific functions

Several modules provide additional functionality, e.g. the latest version of the monochromator module has a button to tell the instrument to go to a home position. These module-specific functions are described on the page of each Module.

Configuration file

Sometimes an instrument has setup-specific properties that are fixed but which must be once set for each instrument. These properties are typically not supported by the user interface of the module. Then, it would be more appropriate to save these configurations in a file that is stored in the public SweepMe! folder. This ensures that the configuration is not lost if a Driver is updated.

There exist convenience functions to load such a configuration file that can be used within a Driver. These functions expect to find a file in the folder "CustomFiles" of the public SweepMe! folder. The file must have the name of the Driver and the extension ".ini". The formatting should be like in any INI file [[2]]

self.isConfigFile() # returns True if the file exists, else False

self.getConfigSections() # returns a list of strings that represent all found sections

self.getConfigOptions(section) # returns a dictionary of key-value pairs of the given section string

self.getConfig() # returns a dictionary with dictionaries of the options for all sections, i.e. the entire config file

A Driver should come with a template configuration file. Starting from version 1.5.5, the user can copy the template configuration file to the "CustomFiles" using the version manager. Inform the user of your Driver about the possibility of customizing the handling via a configuration file by adding some documentation.

Calibrations

SweepMe! version: >= 1.5.5.28

Some modules like Spectrometer or NetworkAnalyzer allow the user to choose a calibration file.

To keep calibration files even if a SweepMe! version is changed or a new driver version is loaded, we recommend putting calibration files into the public SweepMe! folder "CalibrationFiles". You can find the calibration folder using the following line

calibration_folder = self.get_folder("CALIBRATIONS")

Modules that support calibrations, have a button "Find calibrations" which triggers a couple of ways to find calibrations:

1. A Driver can define a list of strings for the key "Calibration" during the method "set_GUIparameter".
2. A Driver can have a function 'get_calibrationfile_properties(port="")' that must return two lists: The first list is a list of strings being the file extensions that the calibration files must have. The second list is a list of strings being characters that the calibration files must contain, e.g. a serial number. The function 'get_calibrationfile_properties(port = "")' must have one argument which is the selected port that might be needed to find the correct calibrations files. All files are searched for in the public SweepMe! folder "Calibration Files". You can create subfolders to organize your calibration files for different instruments or dates you did a calibration. The subfolder name is automatically prepended to the calibrations file name.
3. A Driver can have a function 'find_calibrations()' that must return a list of strings. The function is called together with connect/disconnect so that you can communicate with an instrument to ask for possible calibration options. This might be the case for network analyzers where calibrations are stored on the instrument sometimes.

The selected calibration file name can be accessed via 'get_GUIparameter' via the key "Calibration". To create the full path to the selected calibration file, you have to prepend the path to the public SweepMe! folder "CalibrationFiles". How you handle the calibration file is up to you. Define in your Driver, whether the file is e.g. loaded or just handed over to a third-party library.

We recommend to take Drivers for the modules Spectrometer or NetworkAnalyzer as an example.