System Clock and Uptime¶

Many programs need to know the current date/time (e.g. January 2, 2025 at 14:50 UTC) and/or how long the program has been running (e.g. 2 days, 3 hours, 22 minutes, …).

Time is an essential part of PLC programming. After all, PLC programs run on a timed scan cycle and IEC 61131-3 defines multiple data types to represent dates, times, and durations. However, IEC 61131-3 does not define how to get access to either the system clock or the system uptime. Therefore, vendors offer different mechanisms for programs to query the system clock and update.

System Clock on IronPLC¶

This section is still TODO.

System Uptime on IronPLC¶

When enabled, IronPLC updates the system update into two variables each scan cycle and before any task runs. The default name of these variables are __SYSTEM_UP_TIME and __SYSTEM_UP_LTIME.

These variables are specific to IronPLC so you must enable this feature as a vendor extension using --allow-system-uptime-global or a dialect that enables this feature. See Enabling Dialects and Features for more information about dialects and feature flags.

When enabled, you can write programs that directly reference these variables as external variables, for example:

PROGRAM main
VAR_EXTERNAL
    __SYSTEM_UP_TIME : TIME;
END_VAR
VAR
    elapsed : TIME;
END_VAR
    elapsed := __SYSTEM_UP_TIME;
END_PROGRAM

Vendor Compatibility Shims¶

Code written for other vendor environments typically need a shim so that the code will compile with IronPLC. The shim emulates the POU(s) provided by the vendors library.

Codesys

The TIME function in Codesys returns the system uptime. Follow the steps below to configure IronPLC with equivalent behavior:

Define a function named TIME as follows:

FUNCTION TIME : TIME
   TIME := __SYSTEM_UP_TIME;
END_FUNCTION

Configure IronPLC to use the Codesys dialect. See Enabling Dialects and Features for how to configure the dialect.

RuSTy

The TIME function in RuSTy returns the system uptime. Follow the steps below to configure IronPLC with similar behavior: