s7: explain V1-initial firmware-band fallback to users#721
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gijzelaerr wants to merge 1 commit intomasterfrom
Open
s7: explain V1-initial firmware-band fallback to users#721gijzelaerr wants to merge 1 commit intomasterfrom
gijzelaerr wants to merge 1 commit intomasterfrom
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When a real V1-initial S7-1200 (FW < 4.5) sends Struct(314) for
ServerSessionVersion instead of a scalar, our session-setup echo
can't run, the PLC drops the connection, and the unified Client
falls back to legacy PUT/GET. The previous warning ("PLC did not
provide ServerSessionVersion") was generic enough that users
couldn't tell whether it was a bug, a network issue, or an
unsupported firmware band.
Replace with an actionable message: explains the firmware band,
points at issue #710, and tells users explicitly that db_read /
db_write still work but browse() will not.
Refs #710.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
PLC did not provide ServerSessionVersionwarning with an actionable message that tells users which firmware band hit this case (V1-initial S7-1200, FW < 4.5), what the impact is (db_read/db_write still work, browse() won't), and where to follow the limitation (S7-1200 Session Setup Incomplete #710).Why
The V1-initial S7-1200 firmware band sends a
Struct(314)value forServerSessionVersioninstead of a scalar. Master only handles the scalar case, so the setup-echo can't run, the PLC drops the connection, and the unified Client transparently falls back to legacy PUT/GET. The fall-through is correct, but the previous log line gave users no way to tell whether it was a bug, a network issue, or just an unsupported firmware band.This is the cheap-but-honest path forward chosen in lieu of porting the proprietary HarpoS7-style SessionKey handshake. The full research artefacts live on
research/harpo-port-incompletefor whoever picks that up later.Refs #710.
Test plan
test_s7_unit.pyandtest_s7_v2.pystill pass (97 passed, 6 skipped).s7/connection.py.🤖 Generated with Claude Code