[LinuxPPS] FW: Linux PPS with Garmin 18xLVC using 2.6.35.7 linux Kernel

[Rodolfo Giometti]

On Thu, Oct 28, 2010 at 12:33:14PM -0700, Kent Headley wrote:
> Hi Hal, thanks for your note.
> 
> The PC I'm using (Asus Eee PC) doesn't have any external serial or parallel
> ports. It is a convenient platform of opportunity to try out linuxPPS, so if
> it PPS support can't be done using USB-serial adapters, I'll have to move to
> another platform with real serial ports. Ultimately, I want to use a small
> single board computer, so this was the closest computer I have on hand.
> 
> Does linuxPPS require a 8250/16550 UART?

LinuxPPS just require a real serial port with proper support for DCD
change IRQ. Currently few real serial ports support this.

> So it is NTP that needs the links names gps0 and gpspps0 - thanks for
> clarifying that. 
> 
> The /dev/ttyUSB0 device works fine - I can see NMEA messages (e.g. cat

They works fine for serial data but __not__ for PPS!

> /dev/ttyUSB0). Also, utilities like statserial will show that the DCD pin
> (where PPS is connected) is changing reliably. I'm not sure how statserial
> detects DCD changes (interrupts? polling?), but perhaps it's not the same
> mechanism used by linuxPPS.
> 
> It seems like the USB serial device uses a usb serial driver rather than the
> core serial drivers. lsmod shows
> 
>     serial_core 12121   1 8250
>     usbserial   21796   3 keyspan
>     usbcore     96374   7 keyspan, usbserial (and others)
>     pps_ldisc   1358    1
>     pps_core    5257    1 pps_ldisc
> 
> I don't see any dependencies between the pps modules and any serial modules
> though. 
> 
> Does linuxPPS use a particular serial driver (module)?

No, it uses a ldisc.

> How does linuxPPS detect changes in the PPS source (GPIO, serial pin,
> parallel pin, etc.)?

It depends where you connect your PPS source. :)

Ciao,

Rodolfo

-- 

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