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v1.13.21 - GNSS Centisecond Debug Command (2025-12-11)

What Changed?

This release adds a debug command for troubleshooting GNSS timestamp precision issues. The GET_GNSS_CENTISECOND (alias: GET_GNSS_CS) command exposes the raw centisecond value extracted from NMEA sentences, enabling users to diagnose why millisecond/microsecond timestamps may appear static or not updating as expected. This complements the millisecond and microsecond precision commands from v1.13.19.

What's New

Main Feature: GNSS Centisecond Debug Command

What it does: Returns the raw centisecond component (0-99) from the most recent GPRMC NMEA sentence. Each NMEA sentence contains centisecond-precision timing data; this command exposes that value directly for debugging sub-second precision issues.

How to use it:

# Query the current centisecond value
GET_GNSS_CS
# Response: {"centisecond":97}

# Run multiple times to verify the value is updating
GET_GNSS_CS
GET_GNSS_CS
GET_GNSS_CS

Expected behavior:

  • Centisecond value should change (increment or roll over) with each NMEA sentence received
  • If the value never changes, GNSS data is not updating from the hardware
  • If it changes, the millisecond precision calculation is working correctly (ms = centiseconds × 10)

Code example:

// Check if centisecond is updating
uint16_t cs = Command::getInstance().get_gnss_centisecond();
if (cs >= 0 && cs <= 99) {
  Serial.printf("GNSS centiseconds: %d\n", cs);
  Serial.printf("Milliseconds: %d\n", cs * 10);  // convert to ms
}

Installation

Quick Start

# Get the release
git checkout v1.13.21

# Build
task next:build

# Upload
task next:upload

# Check it works
task monitor

What's Different from the Last Version?

✅ Added

  • GET_GNSS_CENTISECOND command (alias: GET_GNSS_CS) - Debug command for GNSS centisecond value inspection
  • Command::get_gnss_centisecond() - Command class method for accessing raw centisecond data
  • Debug-focused documentation for troubleshooting timestamp precision issues

🔧 Changed

  • Enhanced GNSS command suite with low-level debug access to raw timestamp components

Is It Safe to Upgrade?

Backward Compatible: Yes

  • No changes to existing commands or APIs
  • Debug command is purely additive (read-only)
  • All v1.13.19 features remain unchanged
  • No impact on production firmware behavior

Tests Passed

  • ✅ Builds without errors (next profile: 27.4% flash, 36.6% RAM)
  • ✅ GET_GNSS_CS command registered and callable
  • ✅ Centisecond value correctly retrieved from GNSS state
  • ✅ Command response properly formatted in JSON
  • ✅ No additional memory overhead

Release Details

  • Date: 2025-12-11
  • Version: v1.13.21
  • Files Changed: 4
  • include/command.h - Added get_gnss_centisecond() declaration
  • src/command.cpp - Implemented get_gnss_centisecond() method
  • src/command/gnss.cpp - Added handle_get_gnss_centisecond() handler
  • src/command_manager.cpp - Registered GET_GNSS_CS command in dispatch table

Use Cases

Troubleshooting Timestamp Precision Issues

When GET_GNSS_TIME_MS returns static values (e.g., always ending in 970), use this command to verify that the underlying centisecond data is updating:

# Check if millisecond value is static
GET_GNSS_TIME_MS
# Response: {"gnss_time_ms":1765449640970}  # Always ends in 970

# Diagnose by checking raw centisecond
GET_GNSS_CS
# Response: {"centisecond":97}

# Run again - should see different value if GPS is working
GET_GNSS_CS
# Response: {"centisecond":98}  # Value changed → hardware is working

Verifying GNSS Data Updates

Confirm that NMEA sentences are being received and parsed correctly:

  • Static centisecond value → GNSS communication problem
  • Changing centisecond value → GNSS is functioning correctly

Next Steps

  • Phase 7: RTC integration with GNSS time synchronization
  • Phase 8: WiFi time server (NTP) synchronization with GNSS fallback
  • Phase 9: Multi-detector event correlation web dashboard