Agent Patterns: Slaves, Reset, Interrupts and Pipelines · UVM

Part 6 · Agents & Protocol IP · Intermediate

4topics
4lessons

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The agents you have built so far all have the same shape: a sequence decides, a driver obeys, a monitor reports. Real interfaces break that shape in four ways. Some interfaces are answered rather than commanded. Resets arrive while a transfer is half done. Interrupts are not a bus at all. And fast buses keep many transactions in flight at once. Each of those breaks a beginner's driver loop, and each is a favourite senior interview question.

Every pattern in this topic is built on the DMA bench, and all four were run: three on the bench itself and the pipelined driver on a small AXI-style read model.

What you will be able to do

Build a reactive slave agent that answers the DUT with random backpressure, and swap it in with an instance override that touches one agent only.
Make drivers, monitors and the scoreboard survive a reset in the middle of a job, and explain why the scoreboard flushes when reset ends, not when it starts.
Turn an interrupt wire into a passive agent that publishes transactions and triggers events, so tests and sequences never need its virtual interface.
Write a pipelined, out-of-order driver with separate request and response threads, an outstanding table per ID, and correct response routing.

Where each pattern sits in the bench

Block diagram: the DMA env with a reset-aware APB driver and stream driver, a reactive sink agent on the output, a passive interrupt agent feeding a global event that the test waits on, and a reset-aware scoreboard.

The block bench with every phase 4 variant shown at once. Each test swaps in only the variants it needs, through factory overrides; the env source never changes.

The lessons, in order

Lesson	What it covers
Reactive Slave Agents	axis_sink_agent and axis_ready_seq: the driver waits for TVALID and asks a forever sequence how long to stall; dma_backpressure_test.
Reset on the Fly	Reset-aware drivers with an isolated fork, item_done for a held item, killing stimulus, and a scoreboard that flushes when reset ends; dma_reset_test.
Interrupt Agents	A passive irq agent with analysis items and a global uvm_event; level versus edge, W1C clearing, storms and cause coverage; dma_irq_agent_test.
Pipelined and Out-of-Order Drivers	Address and data threads, get versus get_next_item, put_response with set_id_info, and an outstanding table keyed by ID.

Related topics

Up nextReactive Slave Agents

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What you will be able to do

Build a reactive slave agent that answers the DUT with random backpressure, and swap it in with an instance override that touches one agent only.

Make drivers, monitors and the scoreboard survive a reset in the middle of a job, and explain why the scoreboard flushes when reset ends, not when it starts.

Turn an interrupt wire into a passive agent that publishes transactions and triggers events, so tests and sequences never need its virtual interface.

Write a pipelined, out-of-order driver with separate request and response threads, an outstanding table per ID, and correct response routing.

Where each pattern sits in the bench

The block bench with every phase 4 variant shown at once. Each test swaps in only the variants it needs, through factory overrides; the env source never changes.

The lessons, in order

Lesson	What it covers
Reactive Slave Agents	axis_sink_agent and axis_ready_seq: the driver waits for TVALID and asks a forever sequence how long to stall; dma_backpressure_test.
Reset on the Fly	Reset-aware drivers with an isolated fork, item_done for a held item, killing stimulus, and a scoreboard that flushes when reset ends; dma_reset_test.
Interrupt Agents	A passive irq agent with analysis items and a global uvm_event; level versus edge, W1C clearing, storms and cause coverage; dma_irq_agent_test.
Pipelined and Out-of-Order Drivers	Address and data threads, get versus get_next_item, put_response with set_id_info, and an outstanding table keyed by ID.