The operator's keyer is a K3NG — an Arduino running an emulation of the
WinKeyer protocol — which changes the diagnosis and nearly broke it.
Checked against K3NG's own source before anything else, because yesterday's
handshake now FAILS a connect where it used to press on regardless. It is
safe: k3ng_keyer.ino implements admin echo (0x04) and echoes the byte back,
0x13 is a documented no-op, and OPTION_WINKEY_STRICT_HOST_OPEN — on by
default — ignores every byte except 0x00 before host open, so the resync
nulls are dropped harmlessly and the echo probe still gets through.
The real cause is in K3NG's options file, beside the feature itself:
"disabling Automatic Software Reset is highly recommended", and an option
to "discard errant serial port bytes at startup" for when it is not. On an
Arduino, DTR is wired to reset through a capacitor: opening the port reboots
the board into its bootloader. Ours spoke 400 ms later, to a keyer that was
not running yet.
So the retry now waits 2.5 s, which recovers it without an operator pressing
connect twice, and the engine list gains a K3NG entry that skips the doomed
fast attempt altogether. Everything else is identical to a K1EL — same
settings panel, same protocol.
An operator's log showed the whole fault in its first line: "connected on
COM3 — no reply — the keyer did not answer Host Open", followed by seven
configuration commands and two calls sent as Morse. Nothing was listening.
Reporting a link as up and then writing to it regardless is the part worth
fixing; the handshake is why it was down.
K1EL's Application Interface Guide gives the sequence, and we did one step
of it. Now all of it:
- DTR on, RTS OFF. K1EL's own init sets DTR_CONTROL_ENABLE with
RTS_CONTROL_DISABLE, and on a serial WinKeyer those lines ARE the power
supply — DTR feeds the 3.3 V regulator, RTS provides the negative rail.
go.bug.st/serial defaults both to true, so we drove RTS high on every
connect without a line of code saying so.
- 400 ms after the lines come up, for a WK1 still booting off DTR.
- Three 0x13 nulls to resync the command parser. A keyer left part-way
through a command by whoever spoke to it last would absorb Host Open as
a parameter — the everyday cause of a silent WinKeyer, and one the
operator can do nothing about from the outside.
- An echo test (0x00 0x04 0x55) before trusting the port at all. This is
the step that answers "is there a keyer here", and connecting now fails
on it, with the byte that came back when something else replied.
The whole handshake is retried once, since the first attempt's nulls are
what clear a confused parser. Tested against a fake port that reproduces
each failure: absent, mid-command, and echoing but versionless.
rouggy