Hi Richard, thanks for the info. I've continued my investigation of this and was hoping to get your thoughts.
It appears that the increase in the nmea delay value on my realtime system is related to the priority (or niceness value) of this process: ice-gnss-0000:5 >From the ice driver code, this is the process that writes to the GNSS tty. >Giving this process a better priority causes the ts2phc master offset to stay >very stable as it is not waiting for nmea data. My main question is: Should ts2phc be expected to handle these variations in nmea delay without causing the offset to jump? This appears to be less of an issue with the specific device/driver and rather just an issue of running on a realtime system where the nmea delay could be affected by system utilization. Would you be open to me proposing a fix for this in ts2phc or do you think this issue should be addressed by adjusting the driver priority? Thanks for your help, Cole ________________________________ From: Richard Cochran <richardcoch...@gmail.com> Sent: April 15, 2022 2:28 AM To: Cole Walker <ce.wal...@live.com> Cc: Keller, Jacob E <jacob.e.kel...@intel.com>; linuxptp-users@lists.sourceforge.net <linuxptp-users@lists.sourceforge.net> Subject: Re: [Linuxptp-users] ts2phc master offset value periodically spikes On Tue, Apr 12, 2022 at 02:35:17PM -0700, Richard Cochran wrote: > There are patches floating around that convert the tty stuff into a > proper kthread that can be given sched_fifo priority. You'll have to > port those or do something similar yourself. Once upon a time, there was a low latency option for serial ports. At some point, it was removed. In 2015, an attempt was made to restore some kind of low latency performance. https://www.spinics.net/lists/linux-serial/msg17767.html This went nowhere, but in 2019 another attempt was made. https://lore.kernel.org/lkml/20190110101232.9398-1-o.rem...@pengutronix.de/ HTH, Richard
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