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Documentation pps.rst: add PPS generators documentation

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

Signed-off-by: Rodolfo Giometti <giometti@enneenne.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20241108073115.759039-4-giometti@enneenne.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Rodolfo Giometti 2024-11-08 08:31:14 +01:00 • committed by Greg Kroah-Hartman
parent 580afe4acb
commit b14aea0ce0
1 changed files with 40 additions and 0 deletions
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Documentation/driver-api/pps.rst
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@ -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
------------------------