Hardware interview practice

Synchronize a one-outstanding producer and consumer

MediumTestbench ConcurrencySystemVerilog

Implement two finite testbench threads in which the producer may send the next packet only after the consumer acknowledges the previous one. Consumer processing takes 0 through 5 clocks.

Producer-consumer sequence using depth-one data and acknowledgement mailboxes to keep at most one packet outstanding. — A persistent acknowledgement token releases the producer only after the consumer finishes the current packet.

Starting point

Question code

mailbox #(packet) data_mb = new(1);
mailbox #(bit)    ack_mb  = new(1);

Reviewed example

Work through one case

Input

consumer delay = 5 clocks for every packet

Expected output

packet IDs 0 through 9 are received once in order, with at most one packet outstanding

The producer blocks on ack_mb.get() after every put, so it cannot enqueue the next packet until the consumer completes the prior one.

What to cover

Requirements

Block the producer after each data put until one acknowledgment is received.
Have the consumer receive one packet, wait 0 through 5 clocks, and send exactly one acknowledgment.
Transmit packet IDs 0 through 9 exactly once and wait for both threads to finish.
Use persistent mailbox tokens rather than a bare event whose trigger could be missed.