Timing controller and event trigger

The TCU timer determines when enqueued time points trigger. On each TCU rising edge, it checks whether the timing-queue head is due and uses its label to select the corresponding port events.

Connections

• Input: current tick, configured start and TCU period, and the existing timing-queue head.

• Output: a validated TriggeredEvents and TimingPointTriggered record when a time point is due.

• Scheduling: TcuCycleModel::step() runs on each TCU rising edge.

From logical cycle to global tick

step() converts the physical tick to a logical cycle using the epoch start, TCU period and accumulated pause duration. The timing reference defines the conversion and deadline rules.

prepare_trigger() and prepare_admission() validate work against the state at the start of the edge. meets_deadline() checks the admission deadline. step() validates incoming results and pause-duration arithmetic before committing queue changes, results and pause state.

Admission and triggering update separate underflow policies. pause_ combines instruction-supply and synchronization requests; paused_ticks_ advances once per paused edge, even when both apply.

Objects and state

Object or member	Representation	Role
start_	global tick	Start of the current epoch timeline.
paused_ticks_	elapsed simulation ticks	Total delay from paused TCU edges.
Local variable cycle	derived logical cycle	Calculated from current tick, epoch start, period and elapsed pauses.
timing_.front().due	next due cycle	Selects the time point already queued when the edge begins.
closed_	closure state	Input closed after validated EndOfStream; queues may still drain.
admitted_policy_	UnderflowPolicy	Policy after the last admitted point; controls admission of subsequent zero intervals.
triggered_policy_	UnderflowPolicy	Policy after the last triggered point; controls whether an empty queue pauses the timer.
pause_	PauseState	Records instruction-supply and synchronization pauses separately; either pauses the timer.

C++ API.

Reset and errors

A queued point that misses its due edge or a time point enqueued too late raises LateAdmission. Time arithmetic is checked for overflow.

Reset clears the TCU queues, execution flags, pending synchronization requests and accumulated pause duration. The new start follows the session reset rule.

Implementation and tests

Source: tcu.cpp and tcu.hpp.

CTest: control.empty, control.wait_zero, control.atomic, systemc.tcu_trace.

control.empty checks cumulative trigger ticks across empty gaps and late-enqueue rejection. systemc.tcu_trace checks completion and label output in a clocked harness. control.wait_zero checks admission before a zero wait triggers, delayed admission, overlapping pause reasons, return to strict deadlines, closure and reset. control.atomic checks that rejected requests and results leave queued work and execution flags unchanged.