Re: [PATCH 0/5] Enable PPS reporting for USB serial devices

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi.

At the bottom of the description of the patch set, i warn about the latencies and jitter.

I did "real" test with a pps generated by a workstation (i haven't tested with a precise pps yet), so the the jitter don't mean anything. But the magnitude of difference between uart and usb pps isn't negligible (~400µs with uart compared to ~1ms with usb).

Do you think that, depending on the application, such clock instability is a flaw ?

I will run new tests with a precise pps source later.

I will also try to measure the latency of the pss signal through the usb, and see if it is constant. Perhaps we could introduce parameters to add offset to the pps signal used by the kernel consumer (the same way we can add the offset with PPS_FETCH ioctl) later.

Regards.

Paul.

On 09/10/2013 09:31 AM, Rodolfo Giometti wrote:
On Mon, Sep 09, 2013 at 06:01:15PM +0200, Paul Chavent wrote:
Hi.

This series enable the PPS reporting for USB serial devices.

I have nothing against with this solution but consider that reporting
a PPS signal through USB bus may add unknown delays that may vanish
clock stability... as far as I know you should not use USB serial port
with PPS. Have you some statistics about clock stability in a real
implementation?

Ciao,

Rodolfo

--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Media]     [Linux Input]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Old Linux USB Devel Archive]

  Powered by Linux