AXI-Lite AW Channel Capture
Accept the write address independently from write data.
Task
Capture `AWADDR` when `AWVALID && AWREADY` handshakes. Keep an `addr_pending` flag high until the write transaction consumes that saved address.
Examples
- AWVALID=1 and AWREADY=1 → capture AWADDR
- AWVALID=0 → do not overwrite the saved address
Constraints
- Address and data channels are independent.
- Only assert AWREADY when no address is already pending.
- Reset clears addr_pending.
What this problem is testing
A strong answer translates the requirement into synthesizable state and combinational logic, states reset and update semantics precisely, and handles boundary conditions rather than only the nominal case.
Interview habit: before coding, state reset behavior, the state that must be stored, and the conditions that update each output.
Verification plan
- Check reset or initialization before normal operation.
- Exercise the nominal sequence cycle by cycle.
- Test boundaries such as zero, maximum count, wraparound, full/empty, or simultaneous controls when they apply.
- Prove the design holds state when an enable or qualifying condition is absent.
Edge cases worth testing
- VALID held while READY is low.
- READY asserted before VALID.
- Back-to-back transfers without an idle cycle.
Common mistakes
- Incomplete combinational assignments that infer a latch.
- Blocking/non-blocking assignments that do not match combinational versus sequential intent.
- Parameter-width and boundary errors.
- Passing the happy path while missing reset, overflow, simultaneous operations, or illegal requests.
Interview follow-up questions
- How would you parameterize this design without introducing width or boundary bugs?
- What changes if reset timing or polarity changes?
Concepts to review
AXI4-Lite, write-address, handshake
Open AXI-Lite AW Channel Capture in the HDLForge interactive editor.
Related problems
- 2:1 Multiplexer — Easy
- Parameterized Counter — Easy
- Priority Encoder — Medium
- Synchronous FIFO — Hard
- Shift Register — Easy
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