Separate the Linux audio functions into a separate file.

[pitch] / linux_audio.cpp

diff --git a/linux_audio.cpp b/linux_audio.cpp
new file mode 100644 (file)
index 0000000..b76909e
--- /dev/null
+++ b/linux_audio.cpp
@@ -0,0 +1,82 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <linux/soundcard.h>
+
+#include "linux_audio.h"
+
+int get_dsp_fd(int sample_rate, int fft_length, int overlap)
+{
+       int fd = open("/dev/dsp", O_RDWR);
+       if (fd == -1) {
+               perror("/dev/dsp");
+               exit(1);
+       }
+       
+       ioctl(3, SNDCTL_DSP_RESET, 0);
+       
+       int fmt = AFMT_S16_LE;   // FIXME
+       ioctl(fd, SNDCTL_DSP_SETFMT, &fmt);
+
+       int chan = 1;
+       ioctl(fd, SOUND_PCM_WRITE_CHANNELS, &chan);
+       
+       int rate = sample_rate;
+       ioctl(fd, SOUND_PCM_WRITE_RATE, &rate);
+
+       int max_fragments = 2;
+       int frag_shift = ffs(fft_length / overlap) - 1;
+       int fragments = (max_fragments << 16) | frag_shift;
+        ioctl(fd, SNDCTL_DSP_SETFRAGMENT, &fragments);
+       
+       ioctl(3, SNDCTL_DSP_SYNC, 0);
+       
+       return fd;
+}
+
+#if 1
+void read_chunk(int fd, short *in, unsigned num_samples)
+{
+       int ret;
+
+       ret = read(fd, in, num_samples * sizeof(short));
+       if (ret == 0) {
+               printf("EOF\n");
+               exit(0);
+       }
+
+       if (ret != int(num_samples * sizeof(short))) {
+               // blah
+               perror("read");
+               exit(1);
+       }
+}
+#else
+// make a pure 440hz sine for testing
+void read_chunk(int fd, short *in, unsigned num_samples)
+{
+       static double theta = 0.0;
+       for (unsigned i = 0; i < num_samples; ++i) {
+               in[i] = 32768.0 * cos(theta);
+               theta += 2.0 * M_PI * 440.0 / double(SAMPLE_RATE);
+       }
+}
+#endif
+
+void write_sine(int dsp_fd, double freq, unsigned num_samples, unsigned sample_rate) 
+{
+       static double theta = 0.0;
+       short buf[num_samples];
+       
+       for (unsigned i = 0; i < num_samples; ++i) {
+               buf[i] = short(cos(theta) * 16384.0);
+               theta += 2.0 * M_PI * freq / double(sample_rate);
+       }
+
+       write(dsp_fd, buf, num_samples * sizeof(short));
+}
+