add some helper function

ac108_plugin/ac108_help.c

@@ -0,0 +1,77 @@
+#include "ac108_help.h"
+
+void generate_sine(const snd_pcm_channel_area_t *areas, 
+			  snd_pcm_uframes_t offset,
+			  int count, double *_phase)
+{
+	 snd_pcm_format_t format = SND_PCM_FORMAT_S32;	/* sample format */
+	 unsigned int rate = 16000;			/* stream rate */
+	 unsigned int channels = 4;			/* count of channels */
+	 unsigned int buffer_time = 500000;		/* ring buffer length in us */
+	 unsigned int period_time = 100000;		/* period time in us */
+	 double freq = 160;				/* sinusoidal wave frequency in Hz */
+	 int verbose = 0;					/* verbose flag */
+	 int resample = 1;				/* enable alsa-lib resampling */
+	 int period_event = 0;				/* produce poll event after each period */
+		
+	static double max_phase = 2. * M_PI;
+	double phase = *_phase;
+	double step = max_phase*freq/(double)rate;
+	unsigned char *samples[channels];
+	int steps[channels];
+	unsigned int chn;
+	int format_bits = snd_pcm_format_width(format);
+	unsigned int maxval = (1 << (format_bits - 1)) - 1;
+	int bps = format_bits / 8;  /* bytes per sample */
+	int phys_bps = snd_pcm_format_physical_width(format) / 8;
+	int big_endian = snd_pcm_format_big_endian(format) == 1;
+	int to_unsigned = snd_pcm_format_unsigned(format) == 1;
+	int is_float = (format == SND_PCM_FORMAT_FLOAT_LE ||
+			format == SND_PCM_FORMAT_FLOAT_BE);
+
+	/* verify and prepare the contents of areas */
+	for (chn = 0; chn < channels; chn++) {
+		if ((areas[chn].first % 8) != 0) {
+			printf("areas[%i].first == %i, aborting...\n", chn, areas[chn].first);
+			exit(EXIT_FAILURE);
+		}
+		samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
+		if ((areas[chn].step % 16) != 0) {
+			printf("areas[%i].step == %i, aborting...\n", chn, areas[chn].step);
+			exit(EXIT_FAILURE);
+		}
+		steps[chn] = areas[chn].step / 8;
+		samples[chn] += offset * steps[chn];
+	}
+	/* fill the channel areas */
+	while (count-- > 0) {
+		union {
+			float f;
+			int i;
+		} fval;
+		int res, i;
+		if (is_float) {
+			fval.f = sin(phase);
+			res = fval.i;
+		} else
+			res = sin(phase) * maxval;
+		if (to_unsigned)
+			res ^= 1U << (format_bits - 1);
+		for (chn = 0; chn < channels; chn++) {
+			/* Generate data in native endian format */
+			if (big_endian) {
+				for (i = 0; i < bps; i++)
+					*(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
+			} else {
+				for (i = 0; i < bps; i++)
+					*(samples[chn] + i) = (res >>  i * 8) & 0xff;
+			}
+			samples[chn] += steps[chn];
+		}
+		phase += step;
+		if (phase >= max_phase)
+			phase -= max_phase;
+	}
+	*_phase = phase;
+}
+

ac108_plugin/ac108_help.h

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <alsa/asoundlib.h>
+#include <alsa/pcm_external.h>
+#include <alsa/pcm_plugin.h>
+#include <math.h>
+
+void generate_sine(const snd_pcm_channel_area_t *areas,        
+                          snd_pcm_uframes_t offset,
+                          int count, double *_phase);