[LinuxPPS] PPS next steps...

[Rodolfo Giometti]

On Fri, Feb 06, 2009 at 05:53:26PM -0500, George Spelvin wrote:
> >> Let me turn it around... what do you think "cat /dev/pps0" should do?
> >
> > It, eventually, should return pps0 raw data as byte stream.
> 
> Great!  Would you care to propose the byte stream so I can implement it?
> What is the word size and byte order?  Is there any kind of inter-event
> marker, or does the reader just have to count bytes?

I don't need such byte stream, _you_ are the one which wish to use
read() method. :)

> >> Currently it returns -EINVAL.
> >
> > Which not break read(2) semantic at all. :)
> 
> Well, given that I currently have poll(2) indicating that the fd is
> readable, I thought it would be nice if it were...

By ioctl().

> >> I'd like it to print something that cound be fed into perl or gnuplot.
> >
> > f you wish doing something like this, you can do a userland filter
> > which interprets PPS data and print out them into human readable form,
> > but you cannot ask the kernel to it for you since doing like this you
> > are implementing policies and not mechanism as old UNIX school
> > teach. :)
> 
> Huh?  I understand the distinction, but the details of a data format
> are not policy; what data is available is policy.
> 
> For example, by changing the API so that timestamp fetching depends on
> read access and global parameter setting depends on write access, that
> provides a mechanism which allows the policy decision of who's allowed to
> use the PPS system ot be made in user space using familiar file permission
> settings.

Please, propose your patch but keep in mind read(2) semantic.

> The format can be translated.  I just think that read(2) is a more
> convenient (although less portable) mechanism than the PPS API.
> The intent is for it to be equivalent.

I don't understand you: are telling to me that you wish to replace PPS
API in some way? =:-o

Ciao,

Rodolfo

-- 

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