21-JAN-1993 Level 1.5 is an additional requirement that is optional ------------------------------------------------------- COOR can identify some Specific Triggers as requiring a Level 1.5 confirmation. Pure Level 1 Specific Triggers and Specific Triggers requiring a Level 1.5 confirmation can be freely mixed. Pure Level 1 Specific Trigger ----------------------------- A pure Level 1 Specific Trigger only makes a Level 1 requirement on a combination of Level 1 Andor Terms. Level 1 Requirements -------------------- There are a maximum of 256 Andor Terms. Any Specific Trigger can request any Andor Term to be in any state (asserted, negated, don't care). Any number of Andor Terms can be combined. The Level 1 requirements for a Specific Trigger will be considered met for events where each Andor Term is found in its required state (Logical AND). Andor Term Signal ----------------- A Signal is received for each available Andor Term and latched at a fixed time between beam crossings. To be available during the Level 1 Trigger Decision made for a given beam crossing, the Level 1 Trigger Framework must have received the signals in a stable state 1.25 microseconds BEFORE the next beam crossing marker. Specific Trigger Requiring Level 1.5 Confirmation ------------------------------------------------- A Specific Trigger Requiring Level 1.5 Confirmation makes 2 levels of requirements. First, a Level 1 requirement is made on Level 1 Andor Terms, just like for a Pure Level 1 Specific Trigger. Second, a Level 1.5 requirement is made on Level 1.5 Trigger Terms. Level 1.5 requirements ---------------------- There are a maximum of 32 Level 1.5 Terms. Any Specific Trigger can accept a confirmation from any Level 1.5 Term to be only in the asserted state. Any number of Level 1.5 can be combined. The Level 1.5 requirements for a Specific Trigger will be considered met for events where all of the Level 1.5 Term it accepts as a confirmation is found asserted (Logical AND). A Specific Trigger Requiring Level 1.5 Confirmation must first meet its Level 1 Requirements before the framework will even consider its Level 1.5 requirements. Level 1.5 Signal ---------------- Different Level 1.5 confirmations may take different time depending on their meaning and on the event they are describing. Typical time scales are in the range of a few to a hundred microseconds. Due to the asynchronous nature of the Level 1.5 confirmation, two Signals are needed for each available Andor Term. An Information signal and a clock Signal. All Level 1.5 Terms will be examined at a fixed point in time with respect to the beam crossing marker, during each beam crossing cycle for which a Level 1.5 decision is pending. Any Level 1.5 Terms with an accompanying active Done signal will be latched at that time. Once a Level 1.5 Term is latched, it remains latched until the Level 1.5 decision has been resolved. Accepting an event as soon as one Specific Trigger selected it -------------------------------------------------------------- A number of Specific Triggers can simultaneously meet their requirements for a particular event. As soon as at least one Specific Trigger meets all its requirements, the event will be accepted, the Framework will initiate the digitizing of the appropriate Geographic Sections, and the event will be sent to the Level 2 system. If at least one Pure Level 1 Specific Triggers meets its Level 1 Requirements, the event will be immediately accepted. Furthermore no Level 1.5 cycle will be initiated by the Trigger Framework. Rejecting an event when no Specific Trigger selected it ------------------------------------------------------- If no Pure Level 1 Specific Trigger meets its Level 1 Requirements and no Specific Trigger Requiring Level 1.5 Confirmation meets its Level 1 requirements, the event will be immediately rejected. Starting a Level 1.5 confirmation cycle to collect more evidence ---------------------------------------------------------------- If no Pure Level 1 Specific Trigger meets its Level 1 requirements but at least one Specific Trigger Requiring Level 1.5 Confirmation meets its Level 1 requirements, a Level 1.5 confirmation cycle is initiated. The Level 1.5 confirmation cycle will only consider those Specific Trigger Requiring Level 1.5 Confirmation that met their Level 1 requirements for this particular event. Suspending Level 1 activity --------------------------- During the whole Level 1.5 confirmation cycle, all Level 1 activity is suspended. No subsequent beam crossing can generate a Level 1 decision from any of the Specific Triggers until the Level 1.5 cycle is completed. This translates into global dead time for all 32 Specific Triggers. Concluding a Level 1.5 Confirmation Cycle ----------------------------------------- The Trigger Framework will wait until either the Level 1.5 confirmation for one of the Specific Triggers considered accepts the event, or until all of the Level 1.5 confirmations for the Specific Triggers considered reject the event, or until the Level 1.5 Framework times out (in which case the event will be accepted). Rejecting the event when all Level 1.5 Confirmation rejected it --------------------------------------------------------------- If none of the Level 1.5 confirmations for the Specific Trigger considered accepted the event, the event is rejected. The Trigger Framework immediately resumes normal operation and watches each event for matching Level 1 requirements. Accepting the event as soon as a Level 1.5 confirmation accepts it ------------------------------------------------------------------ As soon as a Level 1.5 confirmation for the Specific Trigger considered accepts the event, the corresponding Specific Trigger is considered as having met its Level 1.5 requirements, all Specific Triggers (if any) whose Level 1.5 confirmation rejected the event are considered as not having met their Level 1.5 requirements, and all Specific Triggers (if any) whose Level 1.5 requirements were not yet received are left as having met all their Level 1.5 requirements. Aborting a Level 1.5 Confirmation Cycle --------------------------------------- Additionally, the Trigger Framework will abort a Level 1.5 confirmation cycle after a timeout period of 200 microseconds. A Level 1.5 confirmation cycle will be aborted 200 microseconds after the corresponding Level 1 Decision only if all confirmations received so far (if any) had rejected the event and if the Level 1.5 confirmation cycle is still waiting for more confirmations. When a Level 1.5 confirmation is aborted, all the Specific Triggers with pending confirmations are considered as accepting the event, all Specific Triggers whose confirmation already rejected the event are kept rejected. Specific Trigger Fired Mask --------------------------- Two Specific Trigger Fired Masks are included in the data for each event. The first mask is the "pre-L1.5" mask, while the second mask is the "post-L1.5" mask. These masks drive the Level 2 software filters. Each bit set in the "pre-L1.5" mask identifies a Specific Trigger that met its Level 1 requirements, while each bit set in the "post-L1.5" mask identifies a Specific Trigger which met its Level 1.5 requirements (or was unresolved by Level 1.5 when the Level 1.5 Trigger Framework timed out). This second, "post-L1.5" mask is only useful for events which required Level 1.5 confirmation. Pure Level 1 Specific Trigger ----------------------------- For a Pure Level 1 Specific Trigger the corresponding bit will be set if and only if the Specific Trigger met all its requirements. Specific Trigger Requiring Level 1.5 Confirmation ------------------------------------------------- Additionally for a Specific Trigger Requiring Level 1.5 Confirmation a bit set in the mask means that the Specific Trigger was not rejected by a Level 1.5 confirmation. A bit can be set after the Level 1 Requirements were met for this Specific Trigger and after the Level 1.5 confirmation further accepted the event. But it can also be set after another Specific Trigger automatically accepted the event before confirmation was seeked or received for this Specific Trigger Requiring Level 1.5 Confirmation. A bit corresponding to a Specific Trigger Requiring Level 1.5 Confirmation will not be set in the Specific Trigger Fired Mask when either its Level 1 requirements were not met, or when its Level 1 requirements were met but its Level 1.5 Confirmation rejected the event. notes: ------ we might only wire 8 or 16 Specific Triggers to accept Level 1.5 requirements. the 200 us timeout is arbitrary the 200 us timeout could be one of the (default) Level 1.5 terms as long as: Level 1.5 terms are ANDed timeout ACCEPTS pending confirmations