USB 3.2/3.1/3.0 (link layer)

An independent clean-room USB 3.x SuperSpeed link-layer VIP: a transmitter that sequences header packets and retries them, a separately written receiver that recomputes both CRCs in the CHECK direction and decides delivery on its own, and a passive link checker (usb32`/`, `make usb32_oss`, 25/25 checks). Covers header packets with a 3-bit Header Sequence Number, CRC-16 over the header and CRC-5 over the Link Control Word, link commands (LGOOD_n / LCRD_x / LBAD / LRTY / LGO_Ux / LAU / LXU), credit-based flow control over four buffers in strict A→B→C→D rotation, and the LBAD→LRTY retry. Six rules, each pinned by a per-rule mask to its own injected fault, plus a T0 that proves the CRCs are real — every single-bit flip in the 96-bit header and the 11-bit control word is detected, so no later CRC test can pass against a degenerate function. SCOPE, narrower than the name: line coding is NOT modelled (Gen1 8b/10b is vip-8b10b, and this catalog already carries a full implementation in pcie/; Gen2 128b/132b is vip-128b132b), nor is the LTSSM. The CRC polynomials and seeds are the spec’s; the final bit-mapping onto the serial wire is NOT claimed, because this VIP does not model the wire — so the CRCs verify error-detecting behaviour, not bit-level compatibility with silicon. The sharpest result is a NEGATIVE one: a retried header packet is byte-identical to the original by design, so every rule passes on both copies and passes CORRECTLY — the retry is the protocol working, not an error. Whether the receiver recognised the duplicate or handed it up a second time happens ABOVE the link and never appears on it. T9 asserts BOTH halves: the checker stays silent while a receiver without duplicate detection delivers the same packet twice.

Key Features

• Header packets: 3-bit sequence number, CRC-16 over the header, CRC-5 over the Link Control Word
• Link commands LGOOD_n / LCRD_x / LBAD / LRTY / LGO_Ux / LAU / LXU with real CRC-5
• Credit-based flow control, four buffers, strict A→B→C→D rotation
• LBAD and acknowledgement-timeout retry, with a one-deep duplicate-detection window
• Passive checker, 6 rules, each pinned by a per-rule mask; plus a CRC self-proof
• The duplicate-delivery blind spot named and asserted, not papered over

Standards & Compliance

USB-IF USB 3.2 Specification (back-compat 3.1/3.0) — link layer

Pairs With

Built to lean against these catalog IPs during integration:

• usb2_dev