Ten groups of signals cross NanoSoC's domains, and each has exactly one safe mechanism: FIFOs for the AXI channels, a request-and-acknowledge handshake for the APB bridge, two-flop synchronisers for every single bit. This topic inventories all ten, teaches how to choose the mechanism for a new crossing, and ends with the checklist the review signs. The circuits themselves belong to the CDC & RDC course; this topic decides where they sit and why. For the protocols see Async FIFO CDC and Handshake Protocols Across Domains; for choosing synchronisers see Synchronizer Selection Guide.
Lesson | After it you can... |
|---|---|
Recite all ten crossings with signals and mechanisms. | |
Assign FIFO, handshake or two flops to any new crossing and price it. | |
Run the top-level crossing review and know what evidence closes it. |
Suggested order: top to bottom. Inventory first, because mechanism choice needs the full signal list; then the decision rules with their arithmetic; then the checklist, which assumes both. Readers who design crossing circuits should read the linked CDC lessons alongside the second lesson.
Nothing multi-bit crosses without a handshake or a FIFO, and nothing single-bit crosses without two flops. Clock-gating cells are not crossings.