【文章标题】：Rebuilding a 1995 GPS Time Server so I don’t get Telstra’d 【文章标题】：重构1995年GPS时间服务器，避免重蹈澳洲电信覆辙
【文章正文】： Rebuilding a 1995 GPS Time Server so I don’t get Telstra’d 重构1995年GPS时间服务器，避免重蹈澳洲电信覆辙
In June I purchased this TrueTime XL-AK time server, so I could learn more of the history of GPS-based time. 六月我购入这台TrueTime XL-AK时间服务器，想深入了解GPS授时技术发展史。
I received it on June 22, and just 16 days later a similar GPS time server took down Australia’s cell service for 12 hours! I made a short video about it but put off digging into the TrueTime… until now. 6月22日收货后仅16天，同类GPS时间服务器就导致澳大利亚蜂窝网络瘫痪12小时！我虽制作了短视频解说，但TrueTime的拆解研究直到现在才进行。
Over the past couple weeks, I’ve ‘restomodded’ this device with a Raspberry Pi, to build a stratum 1 NTP Time server, which I’d like to eventually add to the NTP Pool. I found a way to drop in a Pi 5 and GNSS HAT, display the time and GPS status on the built-in 16x2 LCD, show the status on the bicolor LED, and make this box useful again. 过去两周我用树莓派改造这台设备，构建 stratum 1级NTP时间服务器，最终计划加入NTP服务器池。我成功整合了Pi 5和GNSS扩展板，在内置16x2 LCD屏显示时间与GPS状态，通过双色LED指示灯展示运行状态，让这个老设备重获新生。
I lay out more of the hardware details in today’s YouTube video: 更多硬件细节已在今日YouTube视频展示：
But in this post, I’ll show how I configured the Raspberry Pi to work as a stratum 1 NTP time server with: 本文将重点介绍树莓派作为stratum 1级NTP服务器的配置方案：
- Jimmy Paputto’s L1 GNSS HAT
- Jimmy Paputto L1 GNSS扩展板
- Chrony (for time synchronization and NTP services)
- Chrony（时间同步与NTP服务）
- Time and Daytime Protocols
- 时间与Daytime协议
- A Densitron LCD built into the TrueTime XL-AK
- TrueTime XL-AK内置的Densitron液晶屏
- The bicolor LED built into the TrueTime AL-AK
- TrueTime AL-AK双色LED指示灯
- My TrueTime Pi Mounting Bracket
- 自制的TrueTime树莓派支架
I used a Raspberry Pi 5 with 4GB of RAM, but there’s no reason you can’t use a $44 Pi 5 with 1GB of RAM for this project (if all you’re running on it are timing services for a small network). 采用4GB内存的树莓派5，但44美元1GB版本同样适用（仅需为小型网络提供授时服务时）。
My immediate need for this server is to provide time services for VCF Midwest next weekend. As with all my projects, I have parts gathered for months, and assembly usually waits until a week or two before a deadline :) 本周末需为中西部复古计算机展提供授时服务。延续我一贯作风：零件收集数月，最后期限前一两周才突击组装:)
Jimmy Paputto L1 GNSS HAT Jimmy Paputto L1 GNSS扩展板
I mounted the GNSS HAT on top of the Pi using the included GPIO riser and mounting screws. I used screws on the bottom to secure a Raspberry Pi Bumper underneath. 使用配套的GPIO增高柱和螺丝将扩展板固定在树莓派上方，底部加装防震垫片。
After flashing Pi OS ‘Lite’ (no GUI) to a microSD card, I built the Jimmy Paputto GNSS HAT software from source: 刷入无图形界面的Pi OS Lite系统后，从源码编译安装扩展板驱动：
sudo apt -y install build-essential cmake libgpiod-dev python3-dev git clone https://github.com/jimmypaputto/gnsshat.git cd gnsshat mkdir -p build && cd build cmake .. -DBUILD_PYTHON=ON -DBUILD_EXAMPLES=ON make -j$(nproc) sudo make install
This software includes a GNSS data bridge to transfer NMEA sentences (the time and date information) to gpsd and chrony; you could also plug the GNSS HAT’s USB-C port into a USB-A port on the Pi and access the u-blox NEO-M9N directly. 该软件包含GNSS数据桥接功能，可将NMEA语句（时间日期信息）传输至gpsd和chrony；也可通过USB-C转USB-A直连u-blox NEO-M9N模块。
After the install was complete, I followed the guide to set up a Raspberry Pi Time Server with PPS. 安装完成后，参照PPS（脉冲每秒）时间服务器指南进行配置。
Chrony Chrony配置
When it was time to configure Chrony, I used the following settings inside /etc/chrony/chrony.conf: 在/etc/chrony/chrony.conf中配置如下参数：
GNSS + PPS time server
GPS时间通过gpsd共享内存获取
refclock SHM 0 offset 0.0 delay 0.05 refid NMEA noselect
PPS精准边缘计时
refclock PPS /dev/pps0 refid PPS lock NMEA prefer trust poll 3 filter 16
树莓派晶振较稳定但未达TCXO级别
maxclockerror 0.5
Pi 5硬件时间戳提升精度
hwtimestamp *
备用NTP服务器池
pool 0.pool.ntp.org iburst pool 1.pool.ntp.org iburst
允许局域网客户端
allow 10.0.0.0/16
允许Twingate容器路由请求
allow 172.17.0.0/16 maxupdateskew 100.0 makestep 1000 3 rtcsync
忽略>100ms的时钟更新（解决gpsd每31分钟报1秒偏差）
maxchange 0.1 1 -1
I’m accessing my NTP demo setup remotely through Twingate, since I’m dealing with multiple WANs while testing, and it was easier to punch through things like double NAT with a proxying service. 通过Twingate远程访问NTP演示环境，测试期间需处理多WAN口场景，代理服务更易穿透双重NAT。
Restart chrony after updating the configuration: 更新配置后重启服务： sudo systemctl restart chrony
Verify everything’s working with: 验证运行状态： chronyc sources -v chronyc tracking
After measuring chrony metrics for a few days, I tweaked parts of the configuration to match my setupâfor maxclockerror, I reduced it from the default because I was able to stabilize the oscillator frequency with some tweaks to the Pi’s settings. 经数日指标监测后调整配置：通过树莓派参数优化稳定晶振频率，将maxclockerror从默认值降低。
Pi Timekeeping Tweaks 树莓派计时优化
The changes I found especially helpful: 关键优化措施：
- Running the fan at a constant duty cycle
- 风扇恒定占空比运行
- Forcing the Pi’s SoC to run full speed with force_turbo
- force_turbo强制SoC全速运行
- Pinning the kernel PPS interrupts to CPU core 4 (after isolating that core)
- 将内核PPS中断绑定至隔离后的CPU核心4
- Insulating the bottom of the Pi so the oscillator is in a more stable thermal environment
- 底部加装隔热层稳定晶振温度
- Insulating the rest of the Pi by enclosing it in the TrueTime enclosure
- 整体装入TrueTime外壳实现热隔离
Some other things I tried didn’t seem to have a measurable impact, at least over 6-12 hour testing periods. 其他尝试在6-12小时测试周期内未见明显效果。
I highly recommend reading this Austin’s Nerdy Things blog post if you’re interested in this stuff. 推荐阅读Austin’s Nerdy Things技术博客获取更多细节。
Stable Pi Clock 稳定时钟方案
To force the Pi to stay at 2.4 GHz for a more stable thermal environment (since the oscillator is near the SoC, and it is impacted significantly by bursty CPU activity), you can set the force_turbo option. This burns maybe 1W more power continuously, but is worth it if you want a stable oscillator frequency (important for timing). 通过force_turbo选项强制Pi维持2.4GHz频率（晶振邻近SoC，突发负载会显著影响其稳定性）。虽持续增加约1W功耗，但对维持晶振频率稳定性（关键计时指标）至关重要。
Add the following inside /boot/firmware/config.txt and reboot the Pi: 在/boot/firmware/config.txt添加以下内容后重启：