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Re: [lwip-users] Multi-Threaded netconn API TCP application

From: Sylvain Rochet
Subject: Re: [lwip-users] Multi-Threaded netconn API TCP application
Date: Sun, 4 Oct 2015 11:53:28 +0200
User-agent: Mutt/1.5.21 (2010-09-15)


On Thu, Oct 01, 2015 at 04:41:34PM +0300, Darius Babrauskas wrote:
> Maybe, not was supported the Linux port. Strange, that gettimeofday
> CLOCK_REALTIME was used long time.

I don't understand any of that.

> This can damage the test results. Exmp. NTP client can change
> systemtime at each half hour, some seconds, when your testing LWIP.

No, that's not how NTP works on Linux. NTP does not step the system 
time, it makes very small adjustments in the system clock frequency in 
order to slow down or hurry up very very smoothly the system time. 
CLOCK_MONOTONIC is still affected by incremental NTP adjustments.

If you are talking about a NTP client called from time to time to set 
the system clock, e.g: by calling ntpdate in a cronjob, then you are 
doing it wrong, terribly wrong.

Embedded devices are of different concern, NTP is generally not used to 
change a clock input used for timers or scheduler and very few devices 
are adjusting a timer frequency based on the NTP timing data. Therefore 
it is almost only used to output the current date in logs or human 
interfaces, thus we don't care if it goes backward or forward a little 


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