[LinuxPPS] A question about the PPS device.

[Cirilo Bernardo]

On Wed, Jun 25, 2008 at 6:27 PM,  <clemens at dwf.com> wrote:
[snip]
> Using ttyctrl, the current code in the ONCORE driver worked just fine,
> in particular, the PPS device was opened O_RDWR.
> When I installed the #ifdef N_PPS code, it failed, I looked at ttyctrl.c and
> saw that Rudolfo opened the device O_RDONLY, and changed the ONCORE
> open to O_RDONLY, and now it works.
>
> Mumph.
>
> So why does the open in the same process with the set of the line discipline
> have to be READONLY while the one in a different process can be READWRITE?
>
> And since we are both sending/receiving information to the PPSAPI device
> (granted thru IOCTLs) shouldn't it be READWRITE?
>
> If there is a good reason for this, then others need to warned that their open
> of the PPSAPI device needs to be RDONLY.
>
>

As far as I know, the PPS device (/dev/ppsN) should only be "Read
Only".  There is no reason to support a "write" unless you want some
kind of control interface to change some software parameters.

- Cirilo