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DescriptionQ147
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Q147DVASIC interview problem

Verify a cascading flit-collision resolver

TechniquesDVDesignStreamingStackVariable-length output
DifficultyMedium
TopicUVM Components
LanguageSystemVerilog
Requirements4 checkpoints
01

Problem

Write a stack oracle and header check for a framed flit-collision resolver. A right-moving flit is marked R, a left-moving flit L, and only an R survivor followed by an incoming L can collide.

Example input and output

Use this case to check your interpretation
Input
accepted flits=[R5,R3,L4] followed by last
Output
header survivor_count=1,error=0; sole survivor=R5 with last=1
Explanation

L4 first eliminates the smaller opposing R3 and then loses to R5, exercising a two-level collision cascade while preserving survivor order.

02

Requirements (4)

  • Use a stack oracle for one to 16 nonzero direction/magnitude flits, including arbitrary-depth collision cascades.
  • Magnitude zero or a seventeenth flit predicts an error header with survivor_count zero.
  • For a legal frame, require the header count to equal the ordered survivor queue length; an empty result has no data beats.
  • Treat handshake assembly, header-before-data state, output beat checking, reset, and coverage as follow-up scoreboard work.