pps: add parallel port PPS signal generator

Add PPS signal generator which utilizes STROBE pin of a parallel port to send PPS signals. It uses parport abstraction layer and hrtimers to precisely control the signal. Signed-off-by: Alexander Gordeev <[email protected]> Cc: Rodolfo Giometti <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
RyanHsu · Jan 13, 2011 · 563558b · 563558b
1 parent 46b402a
commit 563558b
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diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
@@ -2,16 +2,12 @@
 # PPS generators configuration
 #
 
-if PPS
-
 comment "PPS generators support"
 
 config PPS_GENERATOR_PARPORT
 	tristate "Parallel port PPS signal generator"
-	depends on PARPORT != n && GENERIC_TIME
+	depends on PARPORT
 	help
 	  If you say yes here you get support for a PPS signal generator which
 	  utilizes STROBE pin of a parallel port to send PPS signals. It uses
 	  parport abstraction layer and hrtimers to precisely control the signal.
-
-endif
diff --git a/drivers/pps/generators/pps_gen_parport.c b/drivers/pps/generators/pps_gen_parport.c
@@ -76,8 +76,15 @@ static enum hrtimer_restart hrtimer_event(struct hrtimer *timer)
 	long lim, delta;
 	unsigned long flags;
 
-	/* NB: approx time with blocked interrupts =
-	   send_delay + 3 * SAFETY_INTERVAL */
+	/* We have to disable interrupts here. The idea is to prevent
+	 * other interrupts on the same processor to introduce random
+	 * lags while polling the clock. getnstimeofday() takes <1us on
+	 * most machines while other interrupt handlers can take much
+	 * more potentially.
+	 *
+	 * NB: approx time with blocked interrupts =
+	 * send_delay + 3 * SAFETY_INTERVAL
+	 */
 	local_irq_save(flags);
 
 	/* first of all we get the time stamp... */