Instrument Simulator

A simulator for real hardware. This project provides a server able to spawn multiple simulated devices and serve requests concurrently

This project provides only the required infrastructure to launch a server from a configuration file (YAML, TOML or json) and a means to register third-party device plugins through the python entry point mechanism.

So far, the project provides transports for TCP, UDP and serial line. Support for new transports (ex: USB, GPIB or SPI) is being implemented on a need basis.

PRs are welcome!

Installation

(TL;DR: pip install sinstruments pyyaml toml)

From within your favorite python environment:

$ pip install sinstruments

Additionally, if you want to write YAML configuration files in YAML:

$ pip install pyyaml

...or, for TOML based configuration:

$ pip install toml

Execution

Once installed the server can be run with:

$ sinstruments-server -c <config file name>

The configuration file describes which devices the server should instantiate along with a series of options like the transport(s) each device listens for requests on.

Example

Imagine you need to simulate 2 GE Pace 5000 reachable through a TCP port each and a CryoCon 24C accessible through the serial line.

First, make sure the dependencies are installed with:

$ pip install gepace[simulator] cryoncon[simulator]

Now we can prepare a YAML configuration called simulator.yml:

devices:
- class: Pace
  name: pace-1
  transports:
  - type: tcp
    url: :5000
- class: Pace
  name: pace-2
  transports:
  - type: tcp
    url: :5001
- class: CryoCon
  name: cryocon-1
  transports:
  - type: serial
    url: /tmp/cryocon-1

We are now ready to launch the server:

$ sinstruments-server -c simulator.yml

That's it! You should now be able to connect to any of the Pace devices through TCP or the CryoCon using the local emulated serial line.

Let's try connecting to the first Pace with the nc (aka netcat) linux command line tool and ask for the well known *IDN? SCPI command:

$ nc localhost 5000
*IDN?
GE,Pace5000,204683,1.01A

Device catalog

This is a summary of the known third-party instrumentation libraries which provide their own simulators.

• cryocon
• fast-spinner
• gepace
• icepap
• julabo
• vacuubrand
• xia-pfcu
• Mythen detector (from Dectris) - not publicly available yet

If you wrote a publicly available device feel free complete the above list by creating a PR.

Configuration

The configuration file can be a YAML, TOML or JSON file as long as it translates to a dictionary with the description given below.

In this chapter we will use YAML as a reference example.

The file should contain at least a top-level key called devices. The value needs to be a list of device descriptions:

devices:
  - class: Pace
    name: pace-1
    transports:
    - type: tcp
      url: :5000

Each device description must contain:

• class: Each third-party plugin should describe which text identify itself
• name: a unique name. Each device must be given a unique name at your choice
• transports: a list of transports from where the device is accessible. Most devices provide only one transport.
  • type: Each transport must define its type (supported are tcp, udp, serial)
  • url: the url where the device is listening on

Any other options given to each device are passed directly to the specific plugin object at runtime. Each plugin should describe which additional options it supports and how to use them.

TCP and UDP

For TCP and UDP transports, the url has the <host>:<port> format.

An empty host (like in the above example) is interpreted as 0.0.0.0 (which means listen on all network interfaces). If host is 127.0.0.1 or localhost the device will only be accessible from the machine where the simulator is running.

A port value of 0 means ask the OS to assign a free port (useful for running a test suite). Otherwise must be a valid TCP or UDP port.

Serial line

The url represents a special file which is created by the simulator to simulate a serial line accessible like a /dev/ttyS0 linux serial line file.

This feature is only available in linux and systems for which the pseudo terminal pty is implemented in python.

The url is optional. The simulator will always create a non deterministic name like /dev/pts/4 and it will log this information in case you need to access. This feature is most useful when running a test suite.

You are free to choose any url path you like (ex: /dev/ttyRP10) as long as you are sure the simulator has permissions to create the symbolic file.

Simulating communication delays

For any of the transports (TCP, UDP and serial line) is is possible to do basic simulation of the communication channel speed by providing an additional baudrate parameter to the configuration. Example:

- class: CryoCon
  name: cryocon-1
  transports:
  - type: serial
    url: /tmp/cryocon-1
    baudrate: 9600

Back door

The simulator provides a gevent back door python console which you can activate if you want to access a running simulator process remotely. To activate this feature simply add to the top-level of the configuration the following:

backdoor: ["localhost": 10001]
devices:
  - ...

You are free to choose any other TCP port and bind address. Be aware that this backdoor provides no authentication and makes no attempt to limit what remote users can do. Anyone that can access the server can take any action that the running python process can. Thus, while you may bind to any interface, for security purposes it is recommended that you bind to one only accessible to the local machine, e.g., 127.0.0.1/localhost.

Usage

Once the backdoor is configured and the server is running, in a another terminal, connect with:

$ nc 127.0.0.1 10001
Welcome to Simulator server console.
You can access me through the 'server()' function. Have fun!
>>> print(server())
...

Develop a new simulator

Writting a new device is simple. Let's imagine you want to simulate a SCPI oscilloscope. The only thing you need to do is write a class inheriting from BaseDevice and implement the handle_message(self, message) where you should handle the different commands supported by your device:

# myproject/simulator.py

from sinstruments.simulator import BaseDevice

class Oscilloscope(BaseDevice):

    def handle_message(self, message):
        self._log.info("received request %r", message)
        message = message.strip().decode()
        if message == "*IDN?":
            return b"ACME Inc,O-3000,23l032,3.5A"
        elif message == "*RST":
            self._log.info("Resetting myself!")
        ...

Don't forget to always return bytes! The simulator doesn't make any guesses on how to encode str

Assuming this file simulator.py is part of a python package called myproject, the second thing to do is register your simulator plugin in your setup.py:

setup(
    ...
    entry_points={
        "sinstruments.device": [
            "Oscilloscope=myproject.simulator:Oscilloscope"
        ]
    }
)

You should now be able to launch your simulator by writing a configuration file:

# oscilo.yml

devices:
- class: Oscilloscope
  name: oscilo-1
  transports:
  - type: tcp
    url: :5000

Now launch the server with

$ sinstruments-server -c oscillo.yml

and you should be able to connect with:

$ nc localhost 5000
*IDN?
ACME Inc,O-3000,23l032,3.5A

Configuring message terminator

By default the eol is set to \n. You can change it to any character with:

class Oscilloscope(BaseDevice):

    newline = b"\r"

Request with multiple answers

If your device implements a protocol which answers with multiple (potentially delayed) answers to a single request, you can support this by converting the handle_message() into a generator:

class Oscilloscope(BaseDevice):

    def handle_message(self, message):
        self._log.info("received request %r", message)
        message = message.strip().decode()
        if message == "*IDN?":
            yield b"ACME Inc,O-3000,23l032,3.5A"
        elif message == "*RST":
            self._log.info("Resetting myself!")
        elif message == "GIVE:ME 10":
            for i in range(1, 11):
                yield f"Here's {i}\n".encode()
        ...

Don't forget to always yield bytes! The simulator doesn't make any guesses on how to encode str

Support for specific configuration options

If your simulated device requires additional configuration, it can be supplied through the same YAML file.

Let's say you want to be able to configure if your device is in CONTROL mode at startup. Additionally, if no initial value is configured, it should default to 'OFF'.

First lets add this to our configuration example:

# oscilo.yml

devices:
- class: Oscilloscope
  name: oscilo-1
  control: ON
  transports:
  - type: tcp
    url: :5000

Then, we re-implement our Oscilloscope __init__() to intercept this new parameter and we handle it in handle_message():

class Oscilloscope(BaseDevice):

    def __init__(self, name, **opts):
        self._control = opts.pop("control", "OFF").upper()
        super().__init__(name, **opts)

    def handle_message(self, message):
        ...
        elif message == "CONTROL":
            return f"CONTROL {self._control}\n".encode()
        ...

You are free to add as many options as you want as long as they don't conflict with the reserved keys name, class and transports.

Writing a specific message protocol

Some instruments implement protocols that are not suitably managed by a EOL based message protocol.

The simulator allows you to write your own message protocol. Here is an example:

from sinstruments.simulator import MessageProtocol


class FixSizeProtocol(MessageProtocol):

    Size = 32

    def read_messages(self):
        transport = self.transport
        buff = b''
        while True:
            buff += transport.read(self.channel, size=4096)
            if not buff:
                return
            for i in range(0, len(buff), self.Size):
                message = buff[i:i+self.Size]
                if len(message) < self.Size:
                    buff = message
                    break
                yield message


class Oscilloscope(BaseDevice):

    protocol = FixSizeProtocol

    ...

Pytest fixture

TODO