The SECS-I Protocol FSM now enforces T3 (reply timeout) and T4
(inter-block timeout) directly, instead of leaving them as
upper-layer hooks.
T3: on complete_send, if the block we just acked had W=1, record its
system_bytes in awaiting_reply_sys_ and emit ActionStartTimer{T3}.
deliver_recv cancels T3 when a block arrives whose system_bytes
match the outstanding request. EventTimeout{T3} aborts the FSM with
"T3 reply timeout".
T4: deliver_recv emits ActionStartTimer{T4} whenever the delivered
block has end_block=false. The next block's deliver_recv cancels
the timer; EventTimeout{T4} aborts with "T4 inter-block timeout".
abort() now also cancels T3/T4 and clears the tracking state.
Test changes:
- Old "T3/T4 are FSM-level no-ops" test → REPLACED by four new
tests: T3 arm+expire, T3 arm+matching-reply cancels, T4
arm+expire, T4 arm+next-block cancels.
- Two new observer accessors on Protocol (awaiting_reply,
awaiting_next_block) so the tests can assert tracking state
without poking internals.
COMPLIANCE.md §1a: T3 + T4 rows go ⬜ → ✅.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Adds a complete IO-free SECS-I implementation:
include/secsgem/secsi/header.hpp 10-byte block header (R/W/E bits)
include/secsgem/secsi/block.hpp length + header + body + checksum
include/secsgem/secsi/protocol.hpp half-duplex FSM (ENQ/EOT/ACK/NAK)
src/secsi/* implementations
tests/test_secsi.cpp header, block, multi-block split,
back-to-back FSM drive, RTY,
contention, T2 timeout
The protocol is event-driven (`Event` → `Action` queue), so wiring it
to an asio serial_port is a thin adapter — that lands in the next
commit so this one stays reviewable.
Key design points:
- Master/slave contention: slave yields on simultaneous ENQ (E4 §7.1.4).
- RTY exhaustion raises ActionRaiseError, clears the send queue, resets
to Idle (no zombie state).
- Multi-block assembler validates contiguous 1..N numbering and exclusive
E-bit-on-last invariants — rejects malformed sequences with nullopt.
- Block::checksum is exposed publicly for the receive path's verification.
Tests cover the happy path (back-to-back delivery), error paths
(checksum mismatch, short input, oversize body), retries (NAK chain to
exhaustion), and protocol corner cases (contention, T2 timeout).
secsgem-py implements SECS-I block framing but lacks the explicit RTY
state machine; this commit puts the C++ port ahead on transport
correctness.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
raphael