play-manual-square-wave-instead-of-file (#2)

Remove dependency on external raw audio file.\
Play manual square wave instead.

Reviewed-on: #2
Co-authored-by: bjoernf <bjoern.foersterling@web.de>
Co-committed-by: bjoernf <bjoern.foersterling@web.de>

play_raw_audio.c

@@ -1,4 +1,5 @@
 #include "play_raw_audio.h"
+#include "time_utils.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <pulse/error.h>
@@ -7,6 +8,27 @@
 #include <string.h>
 #include <unistd.h>
 
+// prototypes for static functions
+static int play_square_wave(float frequency, float duration);
+
+int play_manual_alarm() {
+	int err = 0;
+
+	for (int i = 0; i < 3; i++) {
+		for (int i = 0; i < 2; i++) {
+			err = play_square_wave(1000.0, 0.2);
+			if (err != 0) {
+				return err;
+			}
+			sleep_ms(200);
+		}
+		sleep_ms(500);
+	}
+	return 0;
+}
+
+// UNUSED
+// Playing a raw audio file has the downside of depending on a file.
 int play_raw_audio(char file_name[]) {
 	int pa_error = 0;
 	char content[1024] = "";
@@ -42,3 +64,54 @@ int play_raw_audio(char file_name[]) {
 
 	return 0;
 }
+
+// Output a tone with the audio frequency "frequency"
+// for "duration" number of seconds.
+// The sound signals are not sine waves but square waves.
+static int play_square_wave(float frequency, float duration) {
+	const int sample_rate = 44100;
+	const int channel_count = 2;
+	size_t buffer_size = sample_rate * channel_count * duration;
+	short buffer[buffer_size] = {};
+	pa_simple *s;
+
+	pa_sample_spec ss = {
+		.format = PA_SAMPLE_S16LE,
+		.rate = sample_rate,
+		.channels = channel_count,
+	};
+
+	// number of identical consecutive elements
+	// 5 would look like this:
+	// [0,0,0,0,0,32768,32768,32768,32768,32768,0,...]
+	int array_interval = sample_rate / frequency;
+
+	bool square_peak = false;
+	for (int i = 0; i < buffer_size; i++) {
+		if (i % array_interval == 0) {
+			// toggle the value (0 or the max value for a short)
+			square_peak = !square_peak;
+		}
+		if (square_peak) {
+			buffer[i] = SHRT_MAX;
+		} else {
+			buffer[i] = 0;
+		}
+	}
+
+	if (!(s = pa_simple_new(NULL, NULL, PA_STREAM_PLAYBACK, NULL, "playback", &ss, NULL, NULL, &errno))) {
+		fprintf(stderr, "pa_simple_new() failed: %s\n", pa_strerror(errno));
+		return 1;
+	}
+
+	if (pa_simple_write(s, buffer, sizeof(buffer), NULL) < 0) {
+		fprintf(stderr, "pa_simple_write() failed: %s\n", pa_strerror(errno));
+		return 1;
+	}
+
+	pa_simple_drain(s, NULL);
+
+	pa_simple_free(s);
+
+	return 0;
+}