[LinuxPPS] : Re: [Bug 610] Generic NMEA GPS Receiverdriverw/PPS expects PPS after NMEA data (Udo van den Heuvel)

[Cirilo Bernardo]

>>    > And how can I make a simple rule that will *only* make a
>>    > /dev/gps0 -> /dev/ttyS0 because we have a GPS on that port?
>>    > Of course I can add a link to /etc/udev/devices but what would
>>    > be the udev rules method?
>>
>>    I can't answer that one because I don't know how to tell if there
>>    is a GPS on ttyS0. You can schedule a script by using the
>>    RUN= parameter in udev, but it is the script that will need to
>>    determine if ttyS0 is a GPS and create the link using 'ln -s'.
>
> I think this is not realistic at all. You are trying to solve a very
> hard problem. Serial ports are not USB ones, the user must provide
> some informations to the system (think about ISA and PCI boards :).
>
> Ciao,
>
> Rodolfo

Ciao Rodolfo,

  I agree, automatically creating a link to a device which is a GPS
is an impossible task.  I think any relationships should be in a
configuration file and a script should run at boot time.  Even then,
such a scheme is only useful if the devices are permanently connected.
If people unplug from one port and plug into another then the admin
has to remember to change the configuration file and somehow update
links.  This is really the same problem as how do you know which
pps* device connects to which ttyS* device - whoever plugged in the
devices should know, but there is no guarantee you can match them.
I noticed that the parent device name is put into the linuxpps
structure but even that will be of limited use - the board which I
am currently writing a driver for has a PPS which is not asserted on the
ttyS and the PPS driver has no way of knowing what the associated ttyS
is; this has to be determined by the admin.

- Cirilo

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