Pipeline Stall

Concept

A pipeline stall is a temporary halt of instruction progress in a pipelined processor, used to handle hazard conditions. In the Y86-64 PIPE model described in the evidence, a STALL variant avoids data forwarding and instead holds an instruction in the decode stage for up to three cycles when a later pipeline stage creates a data hazard.

First seen 5/26/2026

Last seen 5/26/2026

Evidence 3 chunks

Wiki v1

WIKI

Definition

A pipeline stall is the behavior in which a pipelined processor temporarily prevents an instruction from advancing in order to handle a hazard condition. In the cited Y86-64 PIPE verification work, stalls are described as occurring when the pipeline deals with a hazard condition, and the STALL design variant specifically makes an instruction stall in the decode stage for up to three cycles when an instruction farther down the pipeline imposes a data hazard.

Role in the STALL pipeline variant

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NEIGHBORHOOD

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RELATIONSHIPS

3 connections

PIPE Pipeline Processor ← uses 100% 2e

PIPE uses pipeline stalls to handle hazard conditions when data forwarding is insufficient.

Liveness Verification ← compares with 100% 1e

Liveness verification proves that the pipeline does not stall indefinitely.

Pipeline Hazard ← mentions 100% 1e

Pipeline stalls are used to handle data hazards when no forwarding path is available.

LINKED ENTITIES

1 links

Data Forwarding alternative_to The STALL variant uses no data forwarding and stalls instead; the LF variant adds forwarding to resolve some load/use hazards rather than stalling.

CITATIONS

6 sources

6 citations — click to expand

[1] In the STALL variant, no data forwarding is used; an instruction stalls in the decode stage for up to three cycles when a later pipeline instruction imposes a data hazard. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5

[2] The LF variant adds a forwarding path that allows some load/use hazards to be resolved by data forwarding rather than stalling. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5

[3] Branch-prediction variants such as NT and BTFNT may cancel up to two instructions when a branch is mispredicted, which is distinct from the STALL variant's data-hazard stalling behavior. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5

[4] A pipeline may stall to deal with hazards, but safety verification alone can allow deadlocking or non-progressing processors to pass; liveness verification is needed to show the pipeline does not stall indefinitely. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5

[5] The PIPE verification work treats restrictions on possible pipeline states as predicates over pipeline states and requires such restrictions to be proved invariant from reset and preserved by each processor operation. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5

[6] The evidence gives examples of unreachable or inconsistent pipeline states, including a nop with a regular program register identifier and a ret instruction followed by other instructions rather than by at least three bubbles. Formal Verification of Pipelined Y86-64 Microprocessors with UCLID5