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The GNSS Service reads the receiver (UART 15/13, 115200, 1 KB buffer) from its 50 ms tick and feeds the NMEA parser. With a Fix it sets the clock (GNSS is the most trusted TimeSource) and refreshes it every 10 min. Settings gets GNSS On/Off and the coordinate format (Q64). Off puts the receiver in standby with $PCAS12,65535, renewed hourly; On wakes it with a hot start, $PCAS10,0. Both measured on the device: the output stops within a second, and a command wakes it within a second. Commands: gnss status (Fix, satellites per constellation, bytes and sentences), gnss nmea on|off, gnss send <sentence>, gnss restart. The probe is gone; never drive GPIO 15 (the receiver's output): the first probe's swapped-pin attempt silenced it until a power cycle. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT