[HN Gopher] Building a Stratum 1 Time Server for 16 bit DOS
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       Building a Stratum 1 Time Server for 16 bit DOS
        
       Author : zdw
       Score  : 39 points
       Date   : 2021-11-07 15:51 UTC (2 days ago)
        
 (HTM) web link (www.brutman.com)
 (TXT) w3m dump (www.brutman.com)
        
       | tyingq wrote:
       | I imagine it has lot less latency between the GPS puck and the
       | PC, with no USB-to-RS232, etc.
        
         | willis936 wrote:
         | You typically use a dedicated GPIO pin to read the PPS signal
         | as the authoritative start-of-second.
        
           | toast0 wrote:
           | If 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.
        
           | tyingq wrote:
           | Ah. They appear to be using the RS232 DCD line for that.
        
             | h2odragon wrote:
             | RI can trigger interrupts
        
       | h2odragon wrote:
       | > 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.
        
       | jeffbee wrote:
       | I 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 wrote:
         | Google'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 wrote:
           | > 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 wrote:
         | You 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 wrote:
           | Well, 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.
        
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       (page generated 2021-11-09 23:01 UTC)