diff --git a/ambientd.c3 b/ambientd.c3
index 675d911..6cfd808 100644
--- a/ambientd.c3
+++ b/ambientd.c3
@@ -200,13 +200,24 @@ macro float @bezier(float t)
 
 
 // https://docs.kernel.org/admin-guide/abi-stable-files.html#abi-file-stable-sysfs-class-backlight
-macro int @read_int_from_file(String path) => ((String)file::load_temp(path)[..^2]).to_int() ?? 0;
+macro int? @read_int_from_file(String path) => ((String)file::load_temp(path)[..^2]).to_int();
 macro void @write_int_to_file(String path, int i) => (void)file::save(path, string::tformat("%d\n", i));
-macro int @get_luminance() => @read_int_from_file(light_sensor_path);
-macro int @get_max_backlight() => @read_int_from_file(backlight_path.tconcat("/max_brightness"));
-macro int @get_backlight() => @read_int_from_file(backlight_path.tconcat("/brightness"));
+macro int? @get_luminance() => @read_int_from_file(light_sensor_path);
+macro int? @get_max_backlight() => @read_int_from_file(backlight_path.tconcat("/max_brightness"));
+macro int? @get_backlight() => @read_int_from_file(backlight_path.tconcat("/brightness"));
 macro void @set_backlight(int v) => @write_int_to_file(backlight_path.tconcat("/brightness"), v);
-macro bool @is_screen_on() => @read_int_from_file(backlight_path.tconcat("/bl_power")) == 0;
+macro bool? @is_screen_on() => @read_int_from_file(backlight_path.tconcat("/bl_power")) == 0;
+
+macro @retry_every(#f, int ms = 100)
+{
+	const sz TRIES = 10;
+	for (sz i = 0; i < TRIES; i++) {
+		if (try x = #f) return x;
+		thread::sleep_ms(ms);
+	}
+	io::eprintfn("ERROR: tried to execute '%s' but it failed too many times (%d)", $stringify(#f), TRIES);
+	std::os::exit(1);
+}
 
 
 fn void sigusr1_handler(CInt sig, void* act, void* oldact)
@@ -223,32 +234,50 @@ fn void sigusr1_handler(CInt sig, void* act, void* oldact)
 // TODO: override config file with arguments
 fn void main(String[] args)
 {
+	bool verbose = false;
+	foreach (a : args[1..]) {
+		switch (a) {
+		case "-v":
+			verbose = true;
+			break;
+		case "-h":
+			io::printfn("ambientd [-hv]");
+			std::os::exit(0);
+		default:
+			io::eprintfn("Unrecognized argument: '%s'", a);
+			std::os::exit(1);
+		}
+	}
+
 	update_config();
 
 	posix::install_signal_handler(libc::SIGUSR1, &sigusr1_handler);
 
-	filter.init(@get_luminance());
-	float luminance_old = filter.update(@get_luminance(), 0.0);
-	int brightness_set = @get_backlight();
+	int _l = @get_luminance() ?? 0;
+	filter.init(_l);
+	float luminance_old = filter.update(_l, 0.0);
+	int brightness_set = @retry_every(@get_backlight());
 	int user_offset = 0;
-	int backlight_max = @get_max_backlight();
+	int backlight_max = @get_max_backlight() ?? 0;
 	Time start = time::now();
 
 	while (true) {
-		if (!@is_screen_on()) {
+		if (!@is_screen_on() ?? false) {
 			thread::sleep_ms(5000);
 			continue;
 		}
 
+
+		// Check user offset
+		user_offset = @retry_every(@get_backlight(), update_interval_ms/2) - brightness_set;
+		int _lx = @retry_every(@get_luminance(), update_interval_ms/2);
+
 		Time now = time::now();
 		Time dt = (Time)(now - start);
 
-		// Check user offset
-		user_offset = @get_backlight() - brightness_set;
-
 		// Filtered luminance, depends heavily on the type of sensor, for the CF-SV7
 		// seems to be in lux
-		float luminance = filter.update(@get_luminance(), (float)dt.to_seconds()) * light_sensor_k;
+		float luminance = filter.update(_lx, (float)dt.to_seconds()) * light_sensor_k;
 		// Percent of the luminance received compared to what the panel can output
 		float p = min((luminance/backlight_max_luminance), 1.0f);
 
@@ -258,9 +287,9 @@ fn void main(String[] args)
 		// perceived luminance is non-linear, I think the inverse square law is correct
 		int new_brightness = (int)(math::pow(p*1.1f, 0.5f)*backlight_max);
 		brightness_set = new_brightness;
-		@set_backlight(brightness_set + user_offset);
+		@set_backlight(max(brightness_set + user_offset, 0));
 
-		// io::printfn("%f, %d, %d", luminance, brightness_set, user_offset);
+		if (verbose) io::printfn("%f, %d, %d", luminance, brightness_set, user_offset);
 
 		start = now;
 		thread::sleep_ms(update_interval_ms);