pto.wait_flag

pto.wait_flag is part of the Pipeline Sync instruction set.

Summary

Block the destination pipeline until a matching event is signaled.

Mechanism

pto.wait_flag is the consumer half of the explicit event protocol. The destination pipeline stalls until the matching (SRC_PIPE, DST_PIPE, EVENT_ID) signal becomes visible, after which later work on the destination pipeline may proceed.

Syntax

PTO Assembly Form

wait_flag["SRC_PIPE", "DST_PIPE", "EVENT_ID"]

AS Level 1 (SSA)

pto.wait_flag["SRC_PIPE", "DST_PIPE", "EVENT_ID"]

Inputs

Operand Type Description
SRC_PIPE pipe identifier Pipeline expected to produce the event
DST_PIPE pipe identifier Pipeline that must wait for the event
EVENT_ID event identifier Named event slot that forms the producer-consumer edge

Expected Outputs

Result Type Description
None — This form does not return SSA values; it blocks pipeline progress until the event becomes visible.

Side Effects

Stalls the destination pipeline until the matching event is signaled. Other pipelines may continue according to the target profile.

Constraints

Constraints

  • The selected pipe identifiers and event identifier MUST be valid for the selected target profile.
  • Waiting on an event that is never signaled is an illegal PTO program.
  • Portable code MUST pair each wait with the intended producer-side pto.set_flag.

Exceptions

Exceptions

  • The verifier rejects illegal operand shapes, unsupported pipe or event identifiers, and attribute combinations that are not valid for the selected instruction set or target profile.
  • Any additional illegality stated in the constraints section is also part of the contract.

Target-Profile Restrictions

Target-Profile Restrictions
  • CPU simulation preserves the visible event protocol but may not expose all low-level hazards that motivate it on hardware.
  • A2/A3 and A5 may use different concrete pipe and event spaces; portable code must rely on the documented PTO contract plus the selected target profile.

Examples

pto.wait_flag["PIPE_MTE2", "PIPE_V", "EVENT_ID0"]