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Building a Stratum 1 Time Server for 16 bit DOS
- h2odragon 5y ago> My target machine was a PCjr with an 8088 CPU designed in 1983, so the 8253 is the only timing hardware available. As I recall, that was an issue for some games on those systems.
- tyingq 5y agoI imagine it has lot less latency between the GPS puck and the PC, with no USB-to-RS232, etc.
- willis936 5y agoYou typically use a dedicated GPIO pin to read the PPS signal as the authoritative start-of-second.
- tyingq 5y agoAh. They appear to be using the RS232 DCD line for that.
- toast0 5y agoIf you can, a PPS signal is ideal; sometimes they're not available though (I've got a setup with an LTE modem that includes a GPS signal, but no PPS. Without a PPS signal, and through the many layers, it's kind of meh accuracy, and I wouldn't export its time to anyone, but it's better than nothing when I don't have any external communications.
- jeffbee 5y agoI found it intriguing that time.google.com advertises itself as Stratum 1. I imagined that Stratum 1 servers had to be physically attached to references like atomic clocks, and that the answers from time.google.com are probably served from a layer of devices that are attached by networks to those other hosts. How are the strata actually defined? Is Stratum 1 defined by accuracy or architecture?
- LeoPanthera 5y agoGoogle's NTP servers also feature "leap smear", which skews the clock in order to "smear" a leap second over the course of 24 hours. This means that on days with a leap second, their servers intentionally return the wrong time, off by up to half a second. This does make lazy IT people's job easier, but makes their "stratum 1" claim even less correct.
- toast0 5y ago> This does make lazy IT people's job easier Depends on how lazy you were. If you use a few servers and they don't agree on leap smearing, your leap second day just got a lot more confusing time wise.
- roywashere 5y agoYou can be stratum 1 if you get your data from GPS, as is the author of the article. So if Google puts hardware with GPS receivers all over the world and routes time.google.com to the nearest machine they have a stratum 1 service without having to put atomic clocks in every data center
- jeffbee 5y agoWell, they DO have atomic clocks in every datacenter, so that’s not the issue. But their service architecture just isn’t built to direct public user queries to exactly one unique machine in a datacenter, so I’m positive they are not doing exactly that. So I’m curious what they base their stratum claims on.