syncster-ioc 0.1.2

EPICS IOC for syncronisation applications in Pump-Probe X-ray diffraction

Synchro-State Tracking IOC

This is a simple IOC that tracks the timing synchronization state on specific laser repetition-control hardware. It was written with the Menly Syncro RRE in mind, but the structure is fairly clean and can likely be extended to other devices easily.

About Repetion Control

Repetition control usually determines when a pulsed laser fires. This is at the base of many scientific applications, e.g. pump-probe experiments. It coordinates the firing rate, and point in time, with an external signal -- typically a driving, gate or marker frequency of another device.

The idea is to have a simple state variable exported as an EPICS process variable which indicates whether the system is in a "synchronized" state with the external frequency, and to take limited action as to whether to force or pause the synchronized state.

Quick Start

Either install locally with pip, then start directly from the command line:

$ pip install syncster-ioc
$ syncster-ioc [args]

or start the pre-built image via Podman (or Docker)

$ podman run -ti --rm registry.gitlab.com:kmc3-xpp/syncster-ioc:latest [args]

The IOC State Diagram

The syncro hardware operation is tracked and reflected in the IOC through the following state automaton:

stateDiagram-v2
    [*] --> INIT
    SYNCED --> OFF
    INIT --> OFF
    INIT --> SYNCED
    STRAY --> SYNCED
    OFF --> STRAY
    ERROR --> OFF
    SYNCED --> ERROR
    STRAY --> ERROR
    INIT --> ERROR
    OFF --> ERROR

The state definition is as follows:

• INIT: IOC initialization, determines the state of the synchronization hardware (i.e. whether it's synchronized to the control frequency)

• SYNCED: this is the actual state we're most interested in: it indicates that the hardware is synchronized and any processes depending on it can continue. Showing this is the main purpose of this IOC.

• OFF: if the hardware indicates being non-synchronized, we enter this state. This is a defined "do not rely on synchronization"-state, and, as far as we can control, no synchronization is attempted. (Beware that at this point, syncster-ioc may not have control over whether the hardware actually attempts any synchronization, but in any case, we're not expecting it and not tracking it; we're well-defined "turned off" and stay that way.)

• STRAY: if synchronization is required / requsted / expected (e.g. by user request), we enter this state to wait for it. We only leave this when synchronization is achieved.

• ERROR: can be entered from any state if (defined) erronous behavior is detected. Most commonly this happens if error flags of the hardware are set, or if we've spent too long in STRAY without any synchronization occuring and a timeout was set. We leave ERROR only on explicit user action ("clearing"), and we enter in OFF, where we wait for yet another request as to whether to attempt (to detect or perform) a new synchronization.

• FAIL: for clarity purposed, this state is not indicated in the diagram. However, it exists, and is very similar to ERROR -- the only difference being that there is no returning from FAIL. It indicates a fundamentally broken situation that led to inconsistencies and cannot be solved within the current state of the IOC. Severe manual intervention with IOC restart is required.

State Exported via EPICS PVs

The following EPICS process variables (PVs) are exported:

• {prefix}state: string, indicates one of the above states.
• {prefix}error: string, shows a human-readable error description. This is only valid if ...:state is "ERROR".
• {prefix}clear: if 1 is written here, the error state is cleared, which will trigger the IOC once to proceed away from the "ERROR" state into "OFF".
• {prefox}stray: if 1 is written here, the IOC is triggered to to proceed from "OFF" into "STRAY".

Environment Variables

The IOC reacts to the following (shell) environment variables:

• SYNCSTER_LOG_LEVEL: one of "debug", "info", "warning" or "error"
• SYNCSTER_PREFIX: the IOC EPICS prefix to use (see above). You should include the : character at the end of the prefix, if you intend to use it.
• SYNCSTER_RRE_PORT: USB device to use with the Menly Syncro RRE, e.g. /dev/ttyUSB0.
• SYNCSTER_AUTO_STRAY: if set to "yes", the state automaton will always automatically advance from "OFF" to "STRAY"; this will make it easier e.g. to recover from errors (requiring a single write to a PV instead of two), but will essentially make it imposible to purposely stay in "OFF". Default behavior is not to.
• SYNCSTER_SYNC_TIMEOUT: the number of seconds to wait in "STRAY" for the synchronization to occur in hardware. Defaults to 300, which may be too short for manual synchronization. Setting this to -1 will wait forever, which may not exactly be what you want if you have an automatic synchronization routine and want fall into a defined error state if it fails to produce intended results.

Bugs & Caveats

"Bugs? Where we're going, we don't have... 😎 ...bugs!"