Reserve phase implementation

TimingControl prepares codeword events at the current time point and requests their insertion into the timing and event queues. The current time point accumulates requested positive wait intervals independently of the running timer.

Connections

• Input: ordered ControlOperation calls, enqueue replies, measurement completions and returned feedback credits.

• Output: instruction results, TimingEvents enqueue requests and EndOfStream through ControlLinks.

• Scheduling: Simulator::cpu_edge() receives replies before the CPU attempts its next control instruction.

Preparing and enqueueing events

cw looks up the source port and codeword, validates the resulting events and stores them for the current time point. An acquisition increments the target measurement register’s pending count and reserves result delivery capacity. Several codewords can contribute events to one time point.

A positive wait enqueues the pending time point, waits for acknowledgment, then advances by the requested number of TCU cycles. wait 0 enqueues the current point with permission to wait for subsequent queue entries and opens a new point without adding a requested interval. The TCU separates consecutive zero-interval points by one logical cycle.

execute() dispatches zero waits to execute_zero_wait() and positive waits to advance_time(). Both retain the pending request until acknowledgment.

FMR and the exit ECALL wait for enqueue acknowledgment. FMR then waits for the selected measurement register to become valid. The exit ECALL publishes an EndOfStream message. Only one enqueue request can be pending. A blocked instruction keeps the same ID and operands across retries.

Initial and empty time points follow the instruction completion rules.

Objects and state

Object or member	Representation	Role
time_point_, last_enqueued_time_	Accumulated wait intervals	Their difference is the next requested interval; the TCU resolves the due cycle.
pending_events_, pending_point_, enqueued_	Pending events and status	Retain events and track whether more may be added at this time point.
pending_wait_for_next_, allow_same_time_	Zero-wait status	Retain a zero wait across enqueue retries and permit subsequent codewords without a positive interval.
enqueue_request_	Optional TimingEvents	Fixed request awaiting acknowledgment.
held_	Optional ControlOperation	Retains the blocked instruction and operands.
last_label_, next_event_, closed_	Identifiers and status	Allocate timing labels and event IDs and record completion.

C++ API.

Reset and errors

An event set exceeding staging capacity, per-port width or per-port queue capacity raises Capacity. Accepting a measurement when either delivery path has result_capacity outstanding entries also raises Capacity.

Reset clears pending events, the enqueue request and held instruction, returns the time point to zero and restarts identifiers in the new epoch.

Implementation and tests

Source: timing_control.cpp and timing_control.hpp.

CTest: protocol.timing, protocol.capacity, systemc.use_cases.

Tests check stable instruction identity across retries, exactly one enqueue, time point advancement after acknowledgment, bounded storage, and measurement feedback through wait 0 with delayed CPU submission.