Railway 2014
Page tree

Versions Compared

Old Version 8

changes.mady.by.user Karsten Rathlev

Saved on

compared with

New Version Current

changes.mady.by.user Caroline Butschek

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

  • When attempting to reserve more than one segment (entering a station, passing a junction) a separate protocol for deadlock prevention must be adhered to.
  • In each tick the controller must check if only partial permissions were granted.
  • If partial permission was granted the train waits for one tick and releases all locks.
  • In the following tick the locks are requested again.
  • As a special case the controllers passing through KIO_LN_0 or KIO_LN_1 must wait an additional tick after releasing the requests.
  • Another special case for the KHIC-Controller: A train is at KIO_LN_0 and requests OC_ST_4, IC_ST_0 and the tracks of the IC-Station. If the train gets the permission for OC_ST_4 but not for IC_ST_0 and any of the tracks of the IC-Station, the controller waits for an additional tick before re-requesting, so that a train with a lower priority, which travels along the OC-Circle, can pass. It was observed, that this change makes the traffic more fluent.
  • A sample controller can be found in the repository at /doc/deadlocks/resolve_deadlock.sct 
  • Further deadlock avoidance is implemented in the ICKHS and OCKHS controllers. If the circle ICKH-KHIC-Circle (OCKH-KHOC-Circle) is full (which means, that all trains have the status "brake"), then one of the trains travels the IC-Circle (OC-Circle), to unlock the deadlock. Our tests have shown, that it is still possible, that the same train has to unlock the deadlock again, so that it never reaches its destination, but at least the other trains reach their destination. This concept could also be adapted to the OCOC and ICIC controllers. Use with care, as these controllers have not been tested to exhaust. Basically the controller wraps the ICKH and ICIC (OCKH and OCOC) controller. If the circle is full (checked at hostcode.c), the slightly changed ICKH (OCKH) controller is aborted or not even started, and instead, the ICIC (OCOC) controller is started. At the hostcode.c file, there is an array, which keeps track of the status of all tracks, where 0 means OFF, 1 means REV or FWD and 2 means BRAKE. To keep it simple, the tracks, where the 11-trains are initially standing are initialized with 2.