In June, a vintage TrueTime XL-AK GPS time server from 1995 was acquired to explore the history and technology of GPS-based timekeeping. Shortly after, a similar GPS time server incident disrupted Australia's cellular network for 12 hours, highlighting the importance of reliable and well-managed time servers.
To modernize the device, a Raspberry Pi 5 with 4GB RAM was integrated alongside Jimmy Paputto's L1 GNSS HAT, transforming the unit into a stratum 1 Network Time Protocol (NTP) server. The setup includes displaying GPS status and time on the original 16x2 LCD panel and using the built-in bicolor LED for status indications.
The Raspberry Pi runs a lightweight OS and uses Chrony for time synchronization, configured to utilize GPS data via shared memory and precise pulse-per-second (PPS) signals for accuracy. Additional protocols such as Time and Daytime (RFC 867/868) were enabled to support legacy time services on the network.
To improve timing stability, several hardware and software optimizations were applied. These include running the CPU at a constant 2.4 GHz frequency using the force_turbo setting, maintaining a consistent fan speed to stabilize temperature, isolating PPS interrupts to a dedicated CPU core, and insulating the Pi to reduce thermal fluctuations affecting the oscillator.
The onboard real-time clock (RTC) battery was configured to maintain time during power outages, ensuring the server stays accurate even after shutdowns.
For monitoring, a web-based dashboard was developed to track Chrony statistics, and the vintage LCD was interfaced using wire wrapping techniques for a low-profile connection inside the original chassis.
Additionally, AppleTalk time services were enabled through the netatalk package running in a Docker container, allowing vintage Macintosh computers on the network to synchronize time via AppleTalk protocols.
The project demonstrates how legacy hardware can be revitalized with modern components to provide precise and reliable time services. This is particularly relevant for environments requiring local time servers to reduce dependency on external sources and improve network resilience.
Future plans include designing a custom PCB for easier hardware integration and enabling the original keypad for enhanced user interaction with the time server's displays.