tree c1fc9f1430aeb7d2b73bc0509f85d6477f5c3c26
parent 717c033669ed3ceaee8df57d4562fafcc1a6267a
author Alexander Gordeev <lasaine@lvk.cs.msu.su> 1294880458 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1294934601 -0800

pps: add parallel port PPS client

Add parallel port PPS client.  It uses a standard method for capturing
timestamps for assert edge transitions: getting a timestamp soon after an
interrupt has happened.

This is not a very precise source of time information due to interrupt
handling delays.  However, timestamps for clear edge transitions are much
more precise because the interrupt handler continuously polls hardware
port until the transition is done.

Hardware port operations require only about 1us so the maximum error
should not exceed this value.  This was my primary goal when developing
this client.

Clear edge capture could be disabled using clear_wait parameter.

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>