From: Ben Harris <bjh21@bjh21.me.uk>
Date: Sat, 3 Nov 2018 11:44:05 +0000 (+0000)
Subject: Minimal beginnings of an impulse clock driver.
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=e0641c13b7d36ddab823c1e699f63cac645af8a2;p=clunk.git

Minimal beginnings of an impulse clock driver.

Currently says "tick!" every 30 seconds.
---

e0641c13b7d36ddab823c1e699f63cac645af8a2
diff --git a/README b/README
new file mode 100644
index 0000000..5849875
--- /dev/null
+++ b/README
@@ -0,0 +1,6 @@
+Clunk might one day be a program for driving an impulse electric clock
+from a GPIO line.
+
+The general plan is to generate a pulse every 30 s (at 0 s and 30 s
+past each minute), with extra magic to adjust the clock at startup and
+at the start and end of summer time.
diff --git a/clunk.c b/clunk.c
new file mode 100644
index 0000000..bba7013
--- /dev/null
+++ b/clunk.c
@@ -0,0 +1,42 @@
+#include <err.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <time.h>
+
+static void
+pulse()
+{
+	/* Dummy implementation */
+	printf("tick!\n");
+}
+
+static void
+run()
+{
+	struct timespec ts;
+	struct tm tm;
+
+	while (true) {
+		if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
+			err(1, "clock_gettime");
+		if (localtime_r(&ts.tv_sec, &tm) == NULL)
+			err(1, "localtime_r");
+		/* Round down to the last 30 s. */
+		ts.tv_nsec = 0;
+		ts.tv_sec -= tm.tm_sec % 30;
+		/* Choose when next tick will be. */
+		ts.tv_sec += 30;
+		if (clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &ts, NULL)
+		    != 0)
+			err(1, "clock_nanosleep");
+		pulse();
+	}
+}
+
+int
+main(int argc, char **argv)
+{
+
+	run();
+	return 0;
+}