1 .. Copyright (c) 2019 Intel
3 .. Licensed under the Apache License, Version 2.0 (the "License");
4 .. you may not use this file except in compliance with the License.
5 .. You may obtain a copy of the License at
7 .. http://www.apache.org/licenses/LICENSE-2.0
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11 .. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 .. See the License for the specific language governing permissions and
13 .. limitations under the License.
22 A.5 PTP Synchronization
23 -----------------------
24 Precision Time Protocol (PTP) provides an efficient way to synchronize
25 time on the network nodes. This protocol uses Master-Slave architecture.
26 Grandmaster Clock (Master) is a reference clock for the other nodes,
27 which adapt their clocks to the master.
29 Using Physical Hardware Clock (PHC) from the Grandmaster Clock, NIC port
30 precision timestamp packets can be served for other network nodes. Slave
31 nodes adjust their PHC to the master following the IEEE 1588
34 There are existing implementations of PTP protocol that are widely used
35 in the industry. One of them is PTP for Linux, which is a set of tools
36 providing necessary PTP functionality. There is no need to re-implement
37 the 1588 protocol because PTP for Linux is precise and efficient enough
38 to be used out of the box.
40 To meet xRAN requirements, two tools from PTP for Linux package are
41 required: ptp4l and phc2sys.
43 PTP for Linux\* Requirements
44 ----------------------------
46 PTP for Linux\* introduces some software and hardware requirements. The
47 machine on which the tools will be run needs to use at least a 3.10
48 Kernel version (built-in PTP support). There are several Kernel options
49 that need to be enabled in Kernel configuration:
53 - CONFIG_NETWORK_PHY_TIMESTAMPING
57 Be sure that the Kernel is compiled with these options.
59 For the best precision, PTP uses hardware timestamping. NIC has its own
60 clock, called Physical Hardware Clock (PHC) to read current time just a
61 moment before the packet is sent to minimalize the delays added by the
62 Kernel processing the packet. Not every NIC supports that feature. To
63 confirm that currently attached NIC support Hardware Timestamps, use
64 ethtool with the command:
68 where eth0 is the potential PHC port. The output from the command should
69 say that there is Hardware Timestamps support.
71 To set up PTP for Linux*:
73 1.Download source code::
75 git clone http://git.code.sf.net/p/linuxptp/code linuxptp
79 2.Apply patch (this is required to work around issue with some of the
80 GM PTP packet size.)::
82 diff --git a/msg.c b/msg.c
88 index d1619d4..40d1538
94 @@ -399,9 +399,11 @@ int msg_post_recv(struct ptp_message \*m, int cnt)
96 port_id_post_recv(&m->pdelay_resp.requestingPortIdentity);
104 timestamp_post_recv(m, &m->follow_up.preciseOriginTimestamp);
112 timestamp_post_recv(m, &m->delay_resp.receiveTimestamp);
114 port_id_post_recv(&m->delay_resp.requestingPortIdentity);
118 3.Build and install ptp41::
120 # make && make install
122 4.Modify configs/default.cfg to control frequency of Sync interval to
130 This tool handles all PTP traffic on the provided NIC port and updated
131 PHC. It also determines the Grandmaster Clock and tracks |br|
133 status. This tool can be run as a daemon or as a regular Linux\*
134 application. When the synchronization is reached, it gives output on the
135 screen for precision tracking. The configuration file of ptp4l contains
136 many options that can be set to get the best synchronization precision.
137 Although, even with default.cfg the synchronization quality is good.
139 To start the synchronization process run::
143 ./ptp4l -f ./configs/default.cfg -2 -i <if_name> -m
145 The output below shows what the output on non-master node should look
146 like when synchronization is started. This means that PHC on this
147 machine is synchronized to the master PHC::
149 ptp4l[1434165.358]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
151 ptp4l[1434165.358]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
153 ptp4l[1434166.384]: port 1: new foreign master fcaf6a.fffe.029708-1
155 ptp4l[1434170.352]: selected best master clock fcaf6a.fffe.029708
157 ptp4l[1434170.352]: updating UTC offset to 37
159 ptp4l[1434170.352]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
161 ptp4l[1434171.763]: master offset -5873 s0 freq -18397 path delay 2778
163 ptp4l[1434172.763]: master offset -6088 s2 freq -18612 path delay 2778
165 ptp4l[1434172.763]: port 1: UNCALIBRATED to SLAVE on
166 MASTER_CLOCK_SELECTED
168 ptp4l[1434173.763]: master offset -5886 s2 freq -24498 path delay 2732
170 ptp4l[1434174.763]: master offset 221 s2 freq -20157 path delay 2728
172 ptp4l[1434175.763]: master offset 1911 s2 freq -18401 path delay 2724
174 ptp4l[1434176.763]: master offset 1774 s2 freq -17964 path delay 2728
176 ptp4l[1434177.763]: master offset 1198 s2 freq -18008 path delay 2728
178 ptp4l[1434178.763]: master offset 746 s2 freq -18101 path delay 2755
180 ptp4l[1434179.763]: master offset 218 s2 freq -18405 path delay 2792
182 ptp4l[1434180.763]: master offset 103 s2 freq -18454 path delay 2792
184 ptp4l[1434181.763]: master offset -13 s2 freq -18540 path delay 2813
186 ptp4l[1434182.763]: master offset 9 s2 freq -18521 path delay 2813
188 ptp4l[1434183.763]: master offset 11 s2 freq -18517 path delay 2813
193 The PHC clock is independent from the system clock. Synchronizing only
194 PHC does not make the system clock exactly the same as the master. The
195 xRAN library requires use of the system clock to determine a common
196 point in time on two |br|
197 machines (O-DU and RU) to start transmission at the
198 same moment and keep time frames defined by ORAN Fronthaul |br|
201 This application keeps the system clock updated to PHC. It makes it
202 possible to use POSIX timers as a time reference in xRAN application.
204 Run phc2sys with the command::
208 ./phc2sys -s enp25s0f0 -w -m -R 8
210 Command output will look like::
212 ptp4l[1434165.342]: selected /dev/ptp4 as PTP
214 phc2sys[1434344.651]: CLOCK_REALTIME phc offset 450 s2 freq -39119 delay
217 phc2sys[1434344.776]: CLOCK_REALTIME phc offset 499 s2 freq -38620 delay
220 phc2sys[1434344.902]: CLOCK_REALTIME phc offset 485 s2 freq -38484 delay
223 phc2sys[1434345.027]: CLOCK_REALTIME phc offset 476 s2 freq -38348 delay
226 phc2sys[1434345.153]: CLOCK_REALTIME phc offset 392 s2 freq -38289 delay
229 phc2sys[1434345.278]: CLOCK_REALTIME phc offset 319 s2 freq -38244 delay
232 phc2sys[1434345.404]: CLOCK_REALTIME phc offset 278 s2 freq -38190 delay
235 phc2sys[1434345.529]: CLOCK_REALTIME phc offset 221 s2 freq -38163 delay
238 phc2sys[1434345.654]: CLOCK_REALTIME phc offset 97 s2 freq -38221 delay
241 phc2sys[1434345.780]: CLOCK_REALTIME phc offset 67 s2 freq -38222 delay
244 phc2sys[1434345.905]: CLOCK_REALTIME phc offset 68 s2 freq -38201 delay
247 phc2sys[1434346.031]: CLOCK_REALTIME phc offset 104 s2 freq -38144 delay
250 phc2sys[1434346.156]: CLOCK_REALTIME phc offset 58 s2 freq -38159 delay
253 phc2sys[1434346.281]: CLOCK_REALTIME phc offset 12 s2 freq -38188 delay
256 phc2sys[1434346.407]: CLOCK_REALTIME phc offset -36 s2 freq -38232 delay
259 phc2sys[1434346.532]: CLOCK_REALTIME phc offset -103 s2 freq -38310
265 Configuration C3 27 can be simulated for O-DU using a separate server
266 acting as Fronthaul Network and O-RU at the same time. O-RU server can
267 be configured to relay PTP and act as PTP master for O-DU. Settings
268 below can be used to |br|
269 instantiate this scenario. The difference is that
270 on the O-DU side, the Fronthaul port can be used as the source of PTP as
271 well as for U-plane and C-plane traffic.
273 1.Follow the steps in Section A.6.1 to install PTP on the O-RU server.
275 2.Copy configs/default.cfg to configs/default_slave.cfg and modify the
276 copied file as below::
278 diff --git a/configs/default.cfg b/configs/default.cfg
284 index e23dfd7..f1ecaf1
286 --- a/configs/default.cfg
288 +++ b/configs/default.cfg
318 offsetScaledLogVariance 0xFFFF
328 -dataset_comparison ieee1588
330 +dataset_comparison G.8275.x
332 G.8275.defaultDS.localPriority 128
342 logAnnounceInterval 1
348 operLogSyncInterval 0
350 logMinDelayReqInterval 0
352 logMinPdelayReqInterval 0
354 @@ -37,7 +37,7 @@ G.8275.portDS.localPriority 128
362 -inhibit_pdelay_req 0
364 +#inhibit_pdelay_req 0
372 1.Start slave port toward PTP GM::
374 ./ptp4l -f ./configs/default_slave.cfg -2 -i enp25s0f0 –m
378 ./ptp4l -f ./configs/default_slave.cfg -2 -i enp25s0f0 -m
380 ptp4l[3904470.256]: selected /dev/ptp6 as PTP clock
382 ptp4l[3904470.274]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
384 ptp4l[3904470.275]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
386 ptp4l[3904471.085]: port 1: new foreign master fcaf6a.fffe.029708-1
388 ptp4l[3904475.053]: selected best master clock fcaf6a.fffe.029708
390 ptp4l[3904475.053]: updating UTC offset to 37
392 ptp4l[3904475.053]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
394 ptp4l[3904477.029]: master offset 196 s0 freq -18570 path delay 1109
396 ptp4l[3904478.029]: master offset 212 s2 freq -18554 path delay 1109
398 ptp4l[3904478.029]: port 1: UNCALIBRATED to SLAVE on
399 MASTER_CLOCK_SELECTED
401 ptp4l[3904479.029]: master offset 86 s2 freq -18468 path delay 1109
403 ptp4l[3904480.029]: master offset 23 s2 freq -18505 path delay 1124
405 ptp4l[3904481.029]: master offset 3 s2 freq -18518 path delay 1132
407 ptp4l[3904482.029]: master offset -169 s2 freq -18689 path delay 1141
409 2.Synchronize local timer clock on O-RU for sample application::
411 ./phc2sys -s enp25s0f0 -w -m -R 8
415 ./phc2sys -s enp25s0f0 -w -m -R 8
417 phc2sys[3904510.892]: CLOCK_REALTIME phc offset 343 s0 freq -38967 delay
420 phc2sys[3904511.017]: CLOCK_REALTIME phc offset 368 s2 freq -38767 delay
423 phc2sys[3904511.142]: CLOCK_REALTIME phc offset 339 s2 freq -38428 delay
426 phc2sys[3904511.267]: CLOCK_REALTIME phc offset 298 s2 freq -38368 delay
429 phc2sys[3904511.392]: CLOCK_REALTIME phc offset 239 s2 freq -38337 delay
432 phc2sys[3904511.518]: CLOCK_REALTIME phc offset 145 s2 freq -38360 delay
435 phc2sys[3904511.643]: CLOCK_REALTIME phc offset 106 s2 freq -38355 delay
438 phc2sys[3904511.768]: CLOCK_REALTIME phc offset -30 s2 freq -38459 delay
441 phc2sys[3904511.893]: CLOCK_REALTIME phc offset -92 s2 freq -38530 delay
444 phc2sys[3904512.018]: CLOCK_REALTIME phc offset -173 s2 freq -38639
447 phc2sys[3904512.143]: CLOCK_REALTIME phc offset -246 s2 freq -38764
450 phc2sys[3904512.268]: CLOCK_REALTIME phc offset -300 s2 freq -38892
453 3. Modify configs/default.cfg as shown below to run PTP master on
456 diff --git a/configs/default.cfg b/configs/default.cfg
462 index e23dfd7..c9e9d4c
464 --- a/configs/default.cfg
466 +++ b/configs/default.cfg
468 @@ -15,14 +15,14 @@ free_running 0
476 -dataset_comparison ieee1588
478 +dataset_comparison G.8275.x
480 G.8275.defaultDS.localPriority 128
490 logAnnounceInterval 1
496 operLogSyncInterval 0
498 logMinDelayReqInterval 0
500 logMinPdelayReqInterval 0
502 @@ -37,7 +37,7 @@ G.8275.portDS.localPriority 128
510 -inhibit_pdelay_req 0
512 +#inhibit_pdelay_req 0
520 4.Start PTP master toward O-DU::
522 ./ptp4l -f ./configs/default.cfg -2 -i enp175s0f1 –m
526 ./ptp4l -f ./configs/default.cfg -2 -i enp175s0f1 -m
528 ptp4l[3903857.249]: selected /dev/ptp3 as PTP clock
530 ptp4l[3903857.266]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
532 ptp4l[3903857.267]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
534 ptp4l[3903863.734]: port 1: LISTENING to MASTER on
535 ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES
537 ptp4l[3903863.734]: selected local clock 3cfdfe.fffe.bd005d as best
540 ptp4l[3903863.734]: assuming the grand master role
542 5.Synchronize local NIC PTP master clock to local NIC PTP slave clock::
544 ./phc2sys -c enp175s0f1 -s enp25s0f0 -w -m -R 8
548 ./phc2sys -c enp175s0f1 -s enp25s0f0 -w -m -R 8
550 phc2sys[3904600.332]: enp175s0f1 phc offset 2042 s0 freq -2445 delay
553 phc2sys[3904600.458]: enp175s0f1 phc offset 2070 s2 freq -2223 delay
556 phc2sys[3904600.584]: enp175s0f1 phc offset 2125 s2 freq -98 delay 4505
558 phc2sys[3904600.710]: enp175s0f1 phc offset 1847 s2 freq +262 delay 4518
560 phc2sys[3904600.836]: enp175s0f1 phc offset 1500 s2 freq +469 delay 4515
562 phc2sys[3904600.961]: enp175s0f1 phc offset 1146 s2 freq +565 delay 4547
564 phc2sys[3904601.086]: enp175s0f1 phc offset 877 s2 freq +640 delay 4542
566 phc2sys[3904601.212]: enp175s0f1 phc offset 517 s2 freq +543 delay 4517
568 phc2sys[3904601.337]: enp175s0f1 phc offset 189 s2 freq +370 delay 4510
570 phc2sys[3904601.462]: enp175s0f1 phc offset -125 s2 freq +113 delay 4554
572 phc2sys[3904601.587]: enp175s0f1 phc offset -412 s2 freq -212 delay 4513
574 phc2sys[3904601.712]: enp175s0f1 phc offset -693 s2 freq -617 delay 4519
576 phc2sys[3904601.837]: enp175s0f1 phc offset -878 s2 freq -1009 delay
579 phc2sys[3904601.962]: enp175s0f1 phc offset -965 s2 freq -1360 delay
582 phc2sys[3904602.088]: enp175s0f1 phc offset -1048 s2 freq -1732 delay
585 phc2sys[3904602.213]: enp175s0f1 phc offset -1087 s2 freq -2086 delay
588 phc2sys[3904602.338]: enp175s0f1 phc offset -1014 s2 freq -2339 delay
591 phc2sys[3904602.463]: enp175s0f1 phc offset -1009 s2 freq -2638 delay
594 6. On O-DU Install PTP for Linux tools from source code the same way as
595 on O-RU above but no need to apply the patch for msg.c
597 7. Start slave port toward PTP master from O-RU using the same
598 default_slave.cfg as on O-RU (see above)::
600 ./ptp4l -f ./configs/default_slave.cfg -2 -i enp181s0f0 –m
604 ./ptp4l -f ./configs/default_slave.cfg -2 -i enp181s0f0 -m
606 ptp4l[809092.918]: selected /dev/ptp6 as PTP clock
608 ptp4l[809092.934]: port 1: INITIALIZING to LISTENING on INIT_COMPLETE
610 ptp4l[809092.934]: port 0: INITIALIZING to LISTENING on INIT_COMPLETE
612 ptp4l[809092.949]: port 1: new foreign master 3cfdfe.fffe.bd005d-1
614 ptp4l[809096.949]: selected best master clock 3cfdfe.fffe.bd005d
616 ptp4l[809096.950]: port 1: LISTENING to UNCALIBRATED on RS_SLAVE
618 ptp4l[809098.363]: port 1: UNCALIBRATED to SLAVE on
619 MASTER_CLOCK_SELECTED
621 ptp4l[809099.051]: rms 38643 max 77557 freq +719 +/- 1326 delay 1905 +/-
624 ptp4l[809100.051]: rms 1134 max 1935 freq -103 +/- 680 delay 1891 +/- 4
626 ptp4l[809101.051]: rms 453 max 855 freq +341 +/- 642 delay 1888 +/- 0
628 ptp4l[809102.052]: rms 491 max 772 freq +1120 +/- 752 delay 1702 +/- 0
630 ptp4l[809103.052]: rms 423 max 654 freq +1352 +/- 653 delay 1888 +/- 0
632 ptp4l[809104.052]: rms 412 max 579 freq +1001 +/- 672 delay 1702 +/- 0
634 ptp4l[809105.053]: rms 441 max 672 freq +807 +/- 709 delay 1826 +/- 88
636 ptp4l[809106.053]: rms 422 max 607 freq +1353 +/- 636 delay 1702 +/- 0
638 ptp4l[809107.054]: rms 401 max 466 freq +946 +/- 646 delay 1702 +/- 0
640 ptp4l[809108.055]: rms 401 max 502 freq +912 +/- 659
642 8. Synchronize local clock on O-DU for sample application or l1
645 ./phc2sys -s enp181s0f0 -w -m -R 8
649 ./phc2sys -s enp181s0f0 -w -m -R 8
651 phc2sys[809127.123]: CLOCK_REALTIME phc offset 675 s0 freq -37379 delay
654 phc2sys[809127.249]: CLOCK_REALTIME phc offset 696 s2 freq -37212 delay
657 phc2sys[809127.374]: CLOCK_REALTIME phc offset 630 s2 freq -36582 delay
660 phc2sys[809127.500]: CLOCK_REALTIME phc offset 461 s2 freq -36562 delay
663 phc2sys[809127.625]: CLOCK_REALTIME phc offset 374 s2 freq -36510 delay
666 phc2sys[809127.751]: CLOCK_REALTIME phc offset 122 s2 freq -36650 delay
669 phc2sys[809127.876]: CLOCK_REALTIME phc offset 34 s2 freq -36702 delay
672 phc2sys[809128.002]: CLOCK_REALTIME phc offset -112 s2 freq -36837 delay
675 phc2sys[809128.127]: CLOCK_REALTIME phc offset -160 s2 freq -36919 delay
678 phc2sys[809128.252]: CLOCK_REALTIME phc offset -270 s2 freq -37077 delay
681 phc2sys[809128.378]: CLOCK_REALTIME phc offset -285 s2 freq -37173 delay
684 phc2sys[809128.503]: CLOCK_REALTIME phc offset -349 s2 freq -37322 delay
687 phc2sys[809128.629]: CLOCK_REALTIME phc offset -402 s2 freq -37480 delay
690 phc2sys[809128.754]: CLOCK_REALTIME phc offset -377 s2 freq -37576 delay
693 phc2sys[809128.879]: CLOCK_REALTIME phc offset -467 s2 freq -37779 delay
696 phc2sys[809129.005]: CLOCK_REALTIME phc offset -408 s2 freq -37860 delay
699 phc2sys[809129.130]: CLOCK_REALTIME phc offset -480 s2 freq -38054 delay
702 phc2sys[809129.256]: CLOCK_REALTIME phc offset -350 s2 freq -38068 delay
705 Support in xRAN Library
706 ----------------------------
708 The xRAN library provides an API to check whether PTP for Linux is
709 running correctly. There is a function called xran_is_synchronized(). It
710 checks if ptp4l and phc2sys are running in the system by making PMC tool
711 requests for current port state and comparing it with the expected
712 value. This verification should be done before initialization.
714 *notes. “SLAVE” is the only expected value in this release; only a
715 non-master scenario is supported currently.*
717 .. |image0| image:: media/image3.png
720 .. |image1| image:: media/image8.png
723 .. |image2| image:: media/image10.emf
726 .. |image3| image:: media/image15.png
729 .. |image4| image:: media/image21.JPG