On units whose C6 runs LilyGo's factory ESP-AT image, Wi-Fi died after
about an hour: scans came back empty, Connect did nothing, and only a
reboot helped. The AT worker brought the SDIO link up once at boot and
never again, so a C6 that wedged mid-session left every command timing
out for the rest of the session.
Link health: AT commands now report OK / ERROR / TIMEOUT / BUSY. A
timeout or busy reply asks for a plain "AT" ping; a ping that times out,
or three command timeouts in a row with no answer between them, is a
stall. ERROR replies are answers and never count. Connects to dead hosts
(CIPSTART) and missing CIPSEND prompts only ask for a ping. The decision
logic lives in c6_link_health.h with a host test.
Recovery: on a stall the worker takes the link down at once (queued
requests fail fast, links read closed so the TCP/WS companion servers
prune them), then runs sdio_bring_down + the XL9535 C6 reset +
c6at_begin, the same path as boot. Resets back off 30 s, 60 s, 120 s,
240 s, then every 5 min; 10 min of a healthy link resets the ladder.
After a successful reset it rejoins the last network and the kept
listener want-flag re-arms AT+CIPSERVER, so port 5000 comes back without
app-side changes. The Wi-Fi status reads "reconnecting" meanwhile, and
main.cpp no longer treats the reset as "radio off".
Join/disconnect: one latest-wins slot instead of the 6-deep queue, so
the user's Connect can no longer be dropped behind 10 s retry pairs and
a stale CWQAP can no longer undo a fresh join. c6at_join_busy() gates
main.cpp's retry while a join is pending or running.
Bring-up now also sends AT+SLEEP=0 and sets AT+CWRECONNCFG=5,0 when the
AT build supports it (query first; ERROR on old images is ignored).
The esp-hosted build is unchanged: everything is in the c6_at component
or behind !TDP4_C6_HOSTED.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
