Telnet Debug Log

When Controller firmware is built with CORE_DEBUG_LEVEL set to 1 or higher, the Controller runs a telnet server on port 23 that streams all ESP32 log output to connected clients. The output is identical to what appears on the serial UART — no additional instrumentation is required. This gives developers remote access to live debug output without a USB serial cable.

The server starts automatically after Ethernet connects during startup. If Ethernet is not connected, the server never starts. When CORE_DEBUG_LEVEL is 0 (production builds), the feature is excluded entirely from the firmware — there is no runtime overhead and port 23 is never opened.

Connecting

telnet <device-ip>

Or, if telnet is not available:

nc <device-ip> 23

Upon connecting, a welcome banner is displayed followed by the live log stream. Up to three simultaneous clients may be connected. A fourth connection attempt is silently rejected until a slot becomes available.

Log levels

What you see depends on the CORE_DEBUG_LEVEL value used at compile time:

CORE_DEBUG_LEVEL	Output visible on telnet
1	Errors only
2	Errors + warnings
3	Errors + warnings + info
4	Errors + warnings + info + debug
5	All output (verbose)

See Compile Flags for how to set CORE_DEBUG_LEVEL.

Behavior notes

• UART is preserved. The serial monitor and telnet clients receive the same output simultaneously.
• Disconnecting a client is safe. The Controller detects the disconnected client and frees the slot on the next loop iteration without stalling.
• Production builds are unaffected. All telnet log code is excluded at compile time when CORE_DEBUG_LEVEL=0.