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Q182FreeSystemVerilog

Detect a starving arbiter requester

Difficulty
Medium
Topic
Arbiters
Language
SV
Interview prompt

Question

Add a watchdog that flags any port that remains continuously asserted but ungranted for more than K sampled cycles.

Starting point

Question code

class StarvationWatchdog #(int N = 8);
  function void sample(int grant_idx, bit [N-1:0] reqs);
  function bit port_starving(int port);
  function bit any_starving();
endclass
Reviewed example

Trace one case

Input
K=2; port1 requests without a grant on sampled cycles0,1,2, then wins on cycle3
Expected output
wait counts=1,2,3 with starvation asserted after cycle2; cycle3 clears count and flag

Continuous ungranted assertion increments through cycles with no winner, and an accepted grant resets that port's watchdog state.

What to cover

Requirements

  1. Maintain a wait count and starvation flag per port.
  2. Increment a port only while it requests and does not receive the accepted grant.
  3. Clear a port's state when it wins or stops requesting.
  4. Set a global alert when any per-port count exceeds K.
  5. Count asserted requesters during cycles in which there is no grant.
  6. Expose both per-port status and the global alert.
Continue practicing
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