Commit b14aea0c authored by Rodolfo Giometti's avatar Rodolfo Giometti Committed by Greg Kroah-Hartman
Browse files

Documentation pps.rst: add PPS generators documentation 



This patch adds some examples about how to register a new PPS
generator in the system, and how to manage it.

Signed-off-by: default avatarRodolfo Giometti <giometti@enneenne.com>
Reviewed-by: default avatarBagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20241108073115.759039-4-giometti@enneenne.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 580afe4a

Documentation/driver-api/pps.rst

+40 −0
Original line number Diff line number Diff line
@@ -202,6 +202,46 @@ 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 struct pps_gen_source_info pps_gen_dummy_info = {

            .name                   = "dummy",

            .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

------------------------