linux-kernel - Re: [Intel-wired-lan] [PATCH v5 00/11] Add support for Intel PPS Generator

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Message-ID: <cd42aca9-ac6c-4579-96d5-121a38ebded5@molgen.mpg.de>
Date: Tue, 19 Mar 2024 23:48:17 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
Cc: tglx@...utronix.de, jstultz@...gle.com, giometti@...eenne.com,
 corbet@....net, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 mallikarjunappa.sangannavar@...el.com, alexandre.torgue@...s.st.com,
 perex@...ex.cz, basavaraj.goudar@...el.com, thejesh.reddy.t.r@...el.com,
 christopher.s.hall@...el.com, x86@...nel.org, joabreu@...opsys.com,
 peter.hilber@...nsynergy.com, intel-wired-lan@...ts.osuosl.org,
 subramanian.mohan@...el.com, linux-sound@...r.kernel.org,
 andriy.shevchenko@...ux.intel.com, netdev@...r.kernel.org,
 pandith.n@...el.com, eddie.dong@...el.com, mcoquelin.stm32@...il.com,
 anthony.l.nguyen@...el.com, davem@...emloft.net
Subject: Re: [Intel-wired-lan] [PATCH v5 00/11] Add support for Intel PPS
 Generator

Dear Lakshmi,


Thank you for your patch series.

Am 19.03.24 um 14:05 schrieb lakshmi.sowjanya.d@...el.com:
> From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> 
> The goal of the PPS(Pulse Per Second) hardware/software is to generate a

Please add a space before (.

> signal from the system on a wire so that some third-party hardware can
> observe that signal and judge how close the system's time is to another
> system or piece of hardware.
> 
> Existing methods (like parallel ports) require software to flip a bit at
> just the right time to create a PPS signal. Many things can prevent
> software from doing this precisely. This (Timed I/O) method is better
> because software only "arms" the hardware in advance and then depends on
> the hardware to "fire" and flip the signal at just the right time.
> 
> To generate a PPS signal with this new hardware, the kernel wakes up
> twice a second, once for 1->0 edge and other for the 0->1 edge. It does
> this shortly (~10ms) before the actual change in the signal needs to be
> made. It computes the TSC value at which edge will happen, convert to a
> value hardware understands and program this value to Timed I/O hardware.
> The actual edge transition happens without any further action from the
> kernel.
> 
> The result here is a signal coming out of the system that is roughly
> 1,000 times more accurate than the old methods. If the system is heavily
> loaded, the difference in accuracy is larger in old methods.
> 
> Application Interface:
> The API to use Timed I/O is very simple. It is enabled and disabled by
> writing a '1' or '0' value to the sysfs enable attribute associated with
> the Timed I/O PPS device. Each Timed I/O pin is represented by a PPS
> device. When enabled, a pulse-per-second(PPS) synchronized with the

Please add a space before (.

> system clock is continuously produced on the Timed I/O pin, otherwise it
> is pulled low.
> 
> The Timed I/O signal on the motherboard is enabled in the BIOS setup.

It’d be great if you documented your test setup including the name of 
the system firmware option.


Kind regards,

Paul