4 files changed, 157 insertions, 0 deletions
diff --git a/include/uvcgadget/meson.build b/include/uvcgadget/meson.build
index c79ea18..d5aaf17 100644
--- a/include/uvcgadget/meson.build
+++ b/include/uvcgadget/meson.build
@@ -5,6 +5,7 @@ uvcgadget_public_headers = files([
   'events.h',
   'list.h',
   'stream.h',
+  'timer.h',
   'v4l2-source.h',
   'video-source.h',
   ])
diff --git a/include/uvcgadget/timer.h b/include/uvcgadget/timer.h
new file mode 100644
index 0000000..de93287
--- /dev/null
+++ b/include/uvcgadget/timer.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * libuvcgadget timer utils
+ *
+ * Copyright (C) 2022 Daniel Scally
+ *
+ * Contact: Daniel Scally <dan.scally@ideasonboard.com>
+ */
+
+struct timer;
+
+/*
+ * timer_new - Create a new timer
+ *
+ * Allocates and returns a new struct timer. This must be configured with
+ * timer_set_fps() and then armed with timer_arm(), following which calls to
+ * timer_wait() will block until the expiration of a period as defined by
+ * timer_set_fps().
+ *
+ * Timers allocated with this function should be removed with timer_destroy()
+ */
+struct timer *timer_new(void);
+
+/*
+ * timer_set_fps - Configure the timer's wait period
+ *
+ * Configure the timer to wait for a period of time such that expirations per
+ * second matches @fps
+ */
+void timer_set_fps(struct timer *timer, int fps);
+
+/*
+ * timer_arm
+ *
+ * Arms the timer such that calls to timer_wait() become blocking until the
+ * expiration of a period.
+ */
+int timer_arm(struct timer *timer);
+
+/*
+ * timer_disarm
+ *
+ * Disarms the timer such that calls to timer_wait() return without blocking.
+ */
+int timer_disarm(struct timer *timer);
+
+/*
+ * timer_wait
+ *
+ * If the timer is armed, block until the expiration of a period
+ */
+void timer_wait(struct timer *timer);
+
+/*
+ * timer_destroy
+ *
+ * Close the timer's file descriptor and free the memory
+ */
+void timer_destroy(struct timer *timer);
diff --git a/lib/meson.build b/lib/meson.build
index f6991d5..a0d67d5 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -6,6 +6,7 @@ libuvcgadget_sources = files([
   'jpg-source.c',
   'stream.c',
   'test-source.c',
+  'timer.c',
   'uvc.c',
   'v4l2.c',
   'v4l2-source.c',
diff --git a/lib/timer.c b/lib/timer.c
new file mode 100644
index 0000000..6627656
--- /dev/null
+++ b/lib/timer.c
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * libuvcgadget timer utils
+ *
+ * Copyright (C) 2022 Daniel Scally
+ *
+ * Contact: Daniel Scally <dan.scally@ideasonboard.com>
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/timerfd.h>
+#include <unistd.h>
+
+#include "timer.h"
+
+struct timer {
+        int fd;
+        struct itimerspec settings;
+};
+
+struct timer *timer_new(void)
+{
+        struct timer *timer;
+
+        timer = malloc(sizeof(*timer));
+        if (!timer)
+                return NULL;
+
+        memset(timer, 0, sizeof(*timer));
+
+        timer->fd = timerfd_create(CLOCK_REALTIME, 0);
+        if (timer->fd < 0) {
+		fprintf(stderr, "failed to create timer: %s (%d)\n",
+			strerror(errno), errno);
+		goto err_free_timer;
+	}
+
+        return timer;
+
+err_free_timer:
+        free(timer);
+
+        return NULL;
+}
+
+void timer_set_fps(struct timer *timer, int fps)
+{
+	int ns_per_frame = 1000000000 / fps;
+
+	timer->settings.it_value.tv_nsec = ns_per_frame;
+	timer->settings.it_interval.tv_nsec = ns_per_frame;
+}
+
+int timer_arm(struct timer *timer)
+{
+        int ret;
+
+	ret = timerfd_settime(timer->fd, 0, &timer->settings, NULL);
+	if (ret)
+		fprintf(stderr, "failed to change timer settings: %s (%d)\n",
+			strerror(errno), errno);
+
+        return ret;
+}
+
+int timer_disarm(struct timer *timer)
+{
+	static const struct itimerspec disable_settings = {
+		{ 0, 0 },
+		{ 0, 0 },
+	};
+	int ret;
+
+	ret = timerfd_settime(timer->fd, 0, &disable_settings, NULL);
+	if (ret)
+		fprintf(stderr, "failed to disable timer: %s (%d)\n",
+			strerror(errno), errno);
+
+	return ret;
+}
+
+void timer_wait(struct timer *timer)
+{
+        char read_buf[8];
+
+        read(timer->fd, read_buf, 8);
+}
+
+void timer_destroy(struct timer *timer)
+{
+        close(timer->fd);
+        free(timer);
+}