EXRAIL proposal: Add UNTIL(vpin) function to wait for pin deactivation (complement to AT/AFTER) #493
Description
Summary
I propose adding a new function UNTIL(vpin) as a complement to the existing AFTER(vpin).
Currently:
AT(vpin)blocks until the pin becomes active.AFTER(vpin)blocks until a complete activation–deactivation cycle occurs.
There is no function that waits only for deactivation, which limits certain use cases involving single sensors.
Motivation
The existing AT/AFTER logic was primarily designed for two-sensor track sections, such as using light barriers or entry/exit detectors. However, in many layouts, current detection sensors (Gleisbelegtmelder) are used to monitor track occupancy. These sensors activate a pin as long as current is flowing — meaning a train is present — and deactivate it when the track becomes clear.
In this case:
- There is only one sensor per block.
AFTER(vpin)is not suitable, because it expects both an activation and deactivation event within the same call.- A dedicated
UNTIL(vpin)would allow waiting specifically for the track to become clear again. This is especially useful in scripts like:
AT(BLOCK1) // wait until block is occupied
PRINT("Train detected")
UNTIL(BLOCK1) // wait until block is clear
PRINT("Block clear"); Proposed Behavior
UNTIL(vpin) should:
- Block execution until the given virtual pin becomes inactive.
- Not require a prior activation event (unlike
AFTER(vpin)). - Use the same internal debounce logic as
AFTER(vpin)to handle brief signal drops (e.g., short current interruptions when wheels cross insulation gaps). - Mirror the timing and event-handling structure of existing pin wait functions for consistency.
Benefits
- Extends EXRAIL for track-occupancy-based automation scenarios.
- Enables clean handling of single-sensor sections using current detectors.
- Avoids polling loops and redundant logic for waiting until a track becomes clear.
- Keeps consistency with the design of
ATandAFTER.