From: Ben Harris <bjh21@bjh21.me.uk>
Date: Fri, 23 Nov 2018 23:26:59 +0000 (+0000)
Subject: Enforce a minimum "low" time for the output.
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=ca37924239304e9d1c86347f6a717c6beb245da2;p=clunk.git

Enforce a minimum "low" time for the output.

By sleeping for 250 ms after each pulse, we ensure that even if
CLOCK_REALTIME is suddenly put forward by 29.7 seconds we won't start
a new pulse before the dial has recovered from the last one.
---

diff --git a/clunk.c b/clunk.c
index 7f10dc9..cb31782 100644
--- a/clunk.c
+++ b/clunk.c
@@ -17,6 +17,11 @@
  */
 static long const pulsewidth = 250000000; /* nanoseconds */
 
+/*
+ * Minimum gap between pulses.
+ */
+static long const gapwidth = 250000000; /* nanoseconds */
+
 /*
  * Maximum error to correct by advancing the clock rather than
  * stopping it, in seconds.  The point where it's faster to stop the
@@ -39,6 +44,9 @@ static sigset_t signals_to_block, timing_signals;
 
 static timer_t main_timer;
 
+#define TS_SEC(s) ((struct timespec){.tv_sec = s, .tv_nsec = 0})
+#define TS_NSEC(s) ((struct timespec){.tv_sec = 0, .tv_nsec = s})
+
 static void
 dummy_out(bool state)
 {
@@ -121,17 +129,21 @@ record_tick_finished(void)
 static void
 pulse()
 {
-	struct timespec const ts = { .tv_sec = 0, .tv_nsec = pulsewidth };
 	sigset_t saved_mask;
 
 	if (sigprocmask(SIG_BLOCK, &signals_to_block, &saved_mask) != 0)
 		err(1, "sigprocmask(block)");
 	(*outfn)(true);
 	record_tick();
-	errno = clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL);
+	errno = clock_nanosleep(CLOCK_MONOTONIC, 0,
+				&TS_NSEC(pulsewidth), NULL);
 	if (errno != 0)
 		err(1, "clock_nanosleep");
 	(*outfn)(false);
+	errno = clock_nanosleep(CLOCK_MONOTONIC, 0,
+				&TS_NSEC(gapwidth), NULL);
+	if (errno != 0)
+		err(1, "clock_nanosleep");
 	record_tick_finished();
 	if (sigprocmask(SIG_SETMASK, &saved_mask, NULL) != 0)
 		err(1, "sigprocmask(restore)");