Hardware interview practice

Verify a shared-memory spiral readout

MediumReference ModelsSystemVerilog

Write the spiral oracle and transaction checks for firmware driving a peripheral that freezes a rectangular static RAM (SRAM) tile at START and copies it into a guarded destination.

Starting point

Question code

function automatic void spiral_reference(
  input int unsigned image[][],
  input int unsigned rows,
  input int unsigned cols,
  ref int unsigned expected[$]
);

Reviewed example

Work through one case

Input

frozen 2x3 source=[[1,2,3],[4,5,6]] with guard words around a six-word destination

Expected output

destination writes=[1,2,3,6,5,4]; exactly six writes; both guards unchanged

The accepted START snapshot is traversed clockwise and no DMA write escapes the validated destination interval.

What to cover

Requirements

Validate dimensions, alignment, accessible ranges, non-overlap, and address arithmetic before register access; perform the required cache and barrier sequence.
Predict from the source image copied at accepted START and compare exactly rows times columns destination writes.
Stop after the first bus fault, reject busy START without changing state, and prevent any write or completion after reset.
Check persistent completion interrupt behavior, timeout across tick wrap, and unchanged guard words around the destination.