Documentation/driver-api/pps.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 PPS - Pulse Per Second
22 --------
32 Carrier Detect pin) or to a parallel port (ACK-pin) or to a special
38 GPS receiver as PPS source, to obtain a wallclock-time with
39 sub-millisecond synchronisation to UTC.
43 ------------------
46 CPU GPIO-Pin as physical link to the signal, I encountered a deeper
56 purpose GPIO line. In this case even basic file-related functionality
57 (like read() and write()) makes no sense at all and should not be a
72 ------------------------------
76 the USB stack. Users have reported clock instability around +-1ms when
90 --------------
133 Please see the file drivers/pps/clients/pps-ktimer.c for example code.
137 -------------
147    $ ls -F /sys/class/pps/pps0/
172 -----------------------
175 the pps-ktimer driver (see the client subsection in the PPS configuration menu)
176 and the userland tools available in your distribution's pps-tools package,
177 http://linuxpps.org , or https://github.com/redlab-i/pps-tools.
179 Once you have enabled the compilation of pps-ktimer just modprobe it (if
182    # modprobe pps-ktimer
190    source 0 - assert 1186592699.388832443, sequence: 364 - clear  0.000000000, sequence: 0
191    source 0 - assert 1186592700.388931295, sequence: 365 - clear  0.000000000, sequence: 0
192    source 0 - assert 1186592701.389032765, sequence: 366 - clear  0.000000000, sequence: 0
195 This is available in the pps-tools repository mentioned above.
199 ----------
207 ------------------------
218 	1	STROBE	  *------     *
227 	10	ACK	  *     ------*
235 	18-25	GND	  *-----------*
237 Please note that parallel port interrupt occurs only on high->low transition,
245 delay between assert and clear edge as small as possible to reduce system
248 The delay can be selected using 'delay' pps_gen_parport module parameter.