Reviewing custom IP before subsystem integration

Treat integration as a contract

Reusable IP is more than an RTL directory. A receiving team needs to understand its interfaces, supported configurations, operating assumptions and evidence. The integration review asks whether the block’s contract matches the system that will use it. A feature that works in one environment may require different assumptions in another.

Begin with the intended use. Describe the surrounding bus, clocks, resets, software access and expected traffic. Identify optional features that will be enabled and those that will remain unused. This prevents the integration plan from relying on a configuration that was never part of the supplied verification evidence.

Check the interface details

Review widths, ordering, latency, backpressure, error responses and outstanding transaction limits. For registers, check address alignment, reset values, access permissions and side effects. Make sure the software-visible description and hardware implementation refer to the same revision.

Boundary conditions deserve explicit attention: maximum bursts, zero or minimum lengths, unsupported operations and access during reset or low-power transitions. An integration test should show what happens at these boundaries. A successful nominal transfer does not establish that the system can recover from an error or a blocked interface.

Understand configuration coverage

A parameterized block can have many legal-looking configurations, but not every combination necessarily has evidence. Request the supported range and the configurations actually reviewed. Distinguish syntactically valid settings from product-supported settings. If the desired combination is new, plan the additional verification and implementation checks.

Generated RTL, register descriptions and software headers should be tied to their generator inputs and version. Otherwise one team can update a configuration while another uses stale collateral. A small manifest linking the selected parameters to generated outputs can prevent a surprisingly large class of integration errors.

Review verification and limitations

Ask for the test plan, relevant results, assertions or properties, coverage interpretation and known limitations. The useful question is what the evidence establishes under its assumptions. A report labeled passed is incomplete without the design revision, setup and scope of the checks.

Review how the block was connected in its test environment and compare that with the proposed subsystem. Different reset ordering, traffic contention or error handling can introduce new behaviours. Integration verification should focus on those differences rather than rerunning a block test and assuming it covers the system.

Connect physical and software requirements

Implementation collateral may include timing assumptions, clock relationships, constraints, memory requirements and physical abstracts. Review whether those assumptions are compatible with the target environment. A constraint copied from a different integration can hide a real path if its exceptions are not justified.

Software teams need initialization, interrupt and error-recovery behaviour. They should know which registers can be accessed during transitions and how the device identifies completion or failure. If firmware must follow an ordering rule, make that rule visible in the interface documentation and test it at the hardware/software boundary.

An integration readiness worksheet

Create a matrix with one row per interface and columns for the IP contract, the subsystem expectation, the evidence available and any difference to resolve. Include clocks, resets, power control, software registers, data interfaces and interrupts. A mismatch should have an owner and a proposed resolution rather than being buried in a general integration risk list.

For a data interface, walk through a normal transaction, a stall and an error. For a register interface, include initialization and an access to an unsupported address. For reset, identify the fate of work already accepted by the block. The examples should use the configuration that will actually be integrated, including optional features and width settings.

After the review, classify the block as ready for the next bounded integration step, ready with documented limitations or awaiting specific evidence. Avoid a universal ready label that says nothing about the intended use. Keep the worksheet with the selected collateral revision so that a later IP update can be reviewed as a change rather than starting the entire reasoning process again. This gives the receiving team a practical record of why the integration was considered acceptable and which assumptions it must preserve.

Package an integration decision

A good review ends with a compatibility matrix and a short list of gaps, each with an owner and required evidence. Some gaps may be documentation issues; others require design changes or new verification. Keep those categories distinct so that a missing explanation is not confused with a demonstrated defect.

This brief does not imply that every reusable IP block is silicon-proven or suitable for every process. Qualification, licensing and implementation conditions are specific to the actual IP. The purpose is to make the integration decision explicit before the subsystem depends on assumptions that nobody has accepted.

Include version and compatibility checks in automation where practical. A build should identify which IP revision and generated collateral it consumed. If a required register description or memory model does not match, the integration environment should report that mismatch clearly. This makes a previously reviewed contract easier to preserve as the subsystem evolves.

What to bring. What to review.

Questions before you begin.