inaccuracy issue of clock_nanosleep() with Debian

[sun19...@gmail.com]

I use BeagleboneBlack with Debian, kernel v3.15, and I want to implement an accurate timer on my BBB.
I use clock_nanosleep() to wait for 1 second. However, it always turns to be 1 second and 100~120 microsecond delay. (I measured clock_nanosleep() between clock_gettime() and with oscilloscope.)

I also run linuxPTP (a software that adjusts system clock, CLOCK_REALTIME, to synchronize linux system with PTP.) to synchronize my BBB.

I have no idea how to improve it, should I change linux to real-time linux? (Xenomai or RobertCNelson's patch for linux)
or is there another way (such as software, codes, etc) to get more accuracy timer? (under 1us delay.)

Thanks!

[John Stampfl]

Try the "cycle counter" in the pru.

look in the pru section of the forum

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John Stampfl

[sun19...@gmail.com]

Hello, John,
Excuse me, may I ask that PRU can be used beyond linux system clock?
Because I need to synchronize my BBB with ourter PTP(precision time protocol) message , if PRU using its clock, then the BBB will become asynchronized device.. 

Thanks.





John Stampfl於 2014年7月17日星期四UTC+8下午11時02分32秒寫道：

[John Stampfl]

You also might find accessing the timers from PRU is more accurate

[John Syn]

From: <sun19...@gmail.com>
Reply-To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>
Date: Thursday, July 17, 2014 at 9:10 AM
To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>
Subject: Re: [beagleboard] inaccuracy issue of clock_nanosleep() with Debian

Hello, John,
Excuse me, may I ask that PRU can be used beyond linux system clock?
Because I need to synchronize my BBB with ourter PTP(precision time protocol) message , if PRU using its clock, then the BBB will become asynchronized device.. 

You might find this helpful:

http://processors.wiki.ti.com/index.php/TI81XX_PSP_Ethernet_Switch_User_Guide#IEEE_1588.2F802.1AS_PTP_Support

Regards,

John