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Diffstat (limited to 'Documentation/driver-api/pps.rst')
| -rw-r--r-- | Documentation/driver-api/pps.rst | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/Documentation/driver-api/pps.rst b/Documentation/driver-api/pps.rst index 78dded03e5d8..598729f9cd27 100644 --- a/Documentation/driver-api/pps.rst +++ b/Documentation/driver-api/pps.rst @@ -202,6 +202,45 @@ Sometimes one needs to be able not only to catch PPS signals but to produce them also. For example, running a distributed simulation, which requires computers' clock to be synchronized very tightly. +To do so the class pps-gen has been added. PPS generators can be +registered in the kernel by defining a struct pps_gen_source_info as +follows:: + + static const struct pps_gen_source_info pps_gen_dummy_info = { + .use_system_clock = true, + .get_time = pps_gen_dummy_get_time, + .enable = pps_gen_dummy_enable, + }; + +Where the use_system_clock states if the generator uses the system +clock to generate its pulses, or they are from a peripheral device +clock. Method get_time() is used to query the time stored into the +generator clock, while the method enable() is used to enable or +disable the PPS pulse generation. + +Then calling the function pps_gen_register_source() in your +initialization routine as follows creates a new generator in the +system:: + + pps_gen = pps_gen_register_source(&pps_gen_dummy_info); + +Generators SYSFS support +------------------------ + +If the SYSFS filesystem is enabled in the kernel it provides a new class:: + + $ ls /sys/class/pps-gen/ + pps-gen0/ pps-gen1/ pps-gen2/ + +Every directory is the ID of a PPS generator defined in the system and +inside of it you find several files:: + + $ ls -F /sys/class/pps-gen/pps-gen0/ + dev enable name power/ subsystem@ system time uevent + +To enable the PPS signal generation you can use the command below:: + + $ echo 1 > /sys/class/pps-gen/pps-gen0/enable Parallel port generator ------------------------ @@ -246,3 +285,27 @@ delay between assert and clear edge as small as possible to reduce system latencies. But if it is too small slave won't be able to capture clear edge transition. The default of 30us should be good enough in most situations. The delay can be selected using 'delay' pps_gen_parport module parameter. + + +Intel Timed I/O PPS signal generator +------------------------------------ + +Intel Timed I/O is a high precision device, present on 2019 and newer Intel +CPUs, that can generate PPS signals. + +Timed I/O and system time are both driven by same hardware clock. The signal +is generated with a precision of ~20 nanoseconds. The generated PPS signal +is used to synchronize an external device with system clock. For example, +it can be used to share your clock with a device that receives PPS signal, +generated by Timed I/O device. There are dedicated Timed I/O pins to deliver +the PPS signal to an external device. + +Usage of Intel Timed I/O as PPS generator: + +Start generating PPS signal:: + + $echo 1 > /sys/class/pps-gen/pps-genx/enable + +Stop generating PPS signal:: + + $echo 0 > /sys/class/pps-gen/pps-genx/enable |