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Summary Mock devices for interactive and automated testing of experiment sequencing
Author Mark A. Tsuchida
License LGPL
Platforms All


SequenceTester provides pure-software simulated devices that are designed to check the behavior of code that controls and sequences device action, such as

  • Acquisition engines
  • Virtual devices such as those in the Utilities device adapter
  • MMCore itself
  • Any other code that should perform exact control of devices

The SequenceTester devices themselves don’t make any assumptions about how the devices will be controlled, but instead report the log (history) of all device actions taken prior to image acquisition. This allows automated tests (or a human) to determine if the expected actions were carried out in the expected order.


All devices are peripherals of the hub device THub, of which only one is expected to be created at one time.

The peripherals are TCamera-0, TCamera-1, TShutter-0, TShutter-1, and so on. Two distinct mock devices (-0 and -1) are provided for each device type so that interactions with more than one device can be tested (including things like Multi Camera).

You need to add at least one camera, because the test results are provided in the “acquired” images. The camera devices have these pre-init properties:

  • ImageWidth and ImageHeight determines the size of images produced (this is fixed for simplicity)
  • ImageMode can be:
    • HumanReadable, which draws human-readable text to the images containing the test data, for interactive testing
    • MachineReadable, which places binary data in MsgPack format in the image buffer, for automated testing

The data encoded in the images is essentially the same for the two values of ImageMode. Any data that doesn’t fit in the image size is truncated (this is more of a concern for the human-readable images).

Overview of the produced test data

Here we describe the data rendered in the human-readable text images. See the separate section below for the machine-readable format.

  • HubGlobalPacketNr is the serial index of the image since when the THub devices was created, across all cameras (counting from 0; same hereafter).
  • Next are a few attributes related to how the image came to be produced:
    • camera,name is the name (N.B. not label) of the camera (TCamera-0 or TCamera-1) that produced the image.
    • camera,serialImageNr is the serial index of the image among those produced by the same camera.
    • camera,isSequence is true if the image was produced as part of a sequence acquisition, as opposed to a snap.
    • camera,snapImageNr (only present if camera,isSequence is false) is the serial index of the image among those produced by the same camera via snap.
    • camera,sequenceImageNr (only present if camera,isSequence is true) is the serial index of the image among those produced by the same camera via sequence acquisition.
    • camera, frameNr (only present if camera,isSequence is true) is the serial index of the image among those produced by the same camera in the same sequence acquisition.
  • The State section lists the values of all device parameters at the moment when the image was acquired. The list is sorted lexicographically.
  • The History section lists all changes of device parameters since what was reported in the immediately previous image. This captures every change, even if the same parameter changed values multiple times. Each change is prefixed with a sequential number in brackets.

Recorded parameters

The parameters recorded in the State and history section correspond to the state modeled by each device type. Device name (N.B., not device label) and parameter name are separated by a comma (,).

Some parameters (such as TCamera-0,Binning or TShutter-0,ShutterState) map to Micro-Manager properties, but some (such as TSwitcher-0,GeteOpen or TZStage-0,ZPositionUm) do not.

The Busy parameter

Each device has a Busy parameter with an integer value. A value of 0 means “not busy”.

Every time a request is made to the device that could make the device busy (that is, anything that causes any parameter other than Busy itself to change), the value is incremented (the increment happens just before the parameter change).

Every time the device interface Busy() query is called, the value is decremented. The Busy() call returns true unless the Busy parameter has reached 0.

Calling MMCore’s waitForDevice() (or waitForSystem(), etc.) results in calling the device’s Busy() in a loop until it returns false, which means that the Busy parameter will always reach 0 if all initiated actions have been waited for before the camera starts “exposing”.

If sequencing code initiates a device action but forgets to wait for its completion, the device’s Busy parameter will have a non-zero value in the State section. This usually indicates a bug. An example is starting a stage move but not waiting for the stage device before acquiring an image.

(Note that such bugs are often hard to find when testing with real hardware or DemoCamera, because not all devices become busy on every action begin initiated—and even if they did, it’s not always obvious from the resulting images that the action had not fully completed: for example, failure to wait for focus movement to finish during a Z stack may not always be obvious in the images.)

Real (wall clock) time is not simulated

The SequenceTester devices intentially do not simulate real time behavior. That is, actions that would take significant time in real devices take almost no time, and the devices never sleep to simulate the passage of time.

This is an important design decision, because the point of SequenceTester is to help test whether requests to devices (including waiting for completion) are made in the correct sequence. You don’t want experiment sequencing code to only work when the timing is “realistic” in some sense—you want it to perform logically correct sequencing.

There is also the added advantage that automated tests will run much faster due to the lack of sleeping.

Hardware sequencing simulation

The TZStage-{0,1} devices support simulation of hardware-sequenced Z movements, triggered by a camera.

The TSwitcher-{0,1} devices support simulation of hardware sequencing of the State property, triggered by a camera.

The simulation is of a hardware setup in which the camera emits triggers and the above devices receive them.

These devices have the following properties to configure hardware sequencing:

  • TriggerSequenceMaxLength: if 0, the device does not support hardware sequencing. Otherwise the device reports the given number as the maximum supported sequence length.
  • TriggerSourceDevice: this can be set to TCamera-0 or TCamera-1 (device name, not label).
  • TriggerSourcePort: this can be set to ExposureStartEdge or ExposureStopEdge.

When hardware sequencing takes place, the State section reflects the sequenced values. In the History section, every received trigger is recorded with the pseudo-value (one-shot); for example: [106]TZStage-0,trig-in:ZPositionUm=(one-shot).

Parameter changes caused by hardware triggers do not increment the Busy count of the device.

Autofocus simulation

(To be documented.) Caveat: the autofocus (actually hardware focus-maintenance) behavior simulated may not represent all possible behaviors of real devices. More work may be needed.

Format of the MsgPack test data

Note: This format may change without notice. If a change is made, the new format will be distinguishable by having a map, rather than an array, as the outer-most container and/or having something other than an integer as the first element. Or we might switch entirely to JSON (starting with '{').

Currently, the message (per image) is an array of length 7 with the following elements:

  • 0: Hub-global image (packet) number (a non-negative integer)
  • 1: Camera info: an array of length 5
    • 0: camera name
    • 1: serial image number
    • 2: is sequence (boolean)
    • 3: cumulative image number (for the acquisition type: snap or sequence)
    • 4: frame number (valid for sequence acquisition)
  • 2: Start change counter (start index of change history since previous image)
  • 3: Current change counter (next index of change history)
  • 4: Map of state at start (i.e., in previous image)
    • This is identical to the “current state” (the next item) as of the previous image (empty for the first ever image)
  • 5: Map of current state
    • This is an array of length-2 arrays containing the key and value
      • The key is a length-2 array: device (string) and parameter (string)
      • The value is a length-2 array: type (string) and value:
        • "bool", bool value
        • "int", int value
        • "float", float value
        • "string", str value
        • "one_shot, nil value
  • 6: Change history
    • This is an array of length-3 arrays containing key, value, and index
      • The key and value are in the same format as the state map
      • The index is the global count of previous change events

Caveat: I wrote the above by reading the source code; it may be good to verify before assuming it is 100% correct.

Unfinished work

We ought to have (Python, Java, and possibly C++) libraries to decode the MsgPack data, abstracting away the details of the format, so that we can make changes to the format without having to update all tests that use SequenceTester. Replacing MsgPack with JSON might accomplish the same goal.