Diff: main.cpp

Revision:

0:5176b3dfccd6

Child:

1:0335b5c18618

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Nov 30 09:51:59 2011 +0000
@@ -0,0 +1,81 @@
+// Hello World example for the USBMIDI library
+
+#include "mbed.h"
+#include "USBAudio.h"
+#include "CircBuffer.h"
+
+Serial pc(USBTX, USBRX);
+
+// frequency: 48 kHz
+#define FREQ 48000
+
+// 1 channel: mono
+#define NB_CHA 1
+
+// length of an audio packet: each ms, we receive 48 * 16bits ->48 * 2 bytes. as there is one channel, the length will be 48 * 2 * 1
+#define LENGTH_AUDIO_PACKET 48 * 2 * 1
+
+// USBAudio
+USBAudio audio(FREQ, NB_CHA, 0x7180, 0x7500);
+
+// speaker connected to the AnalogOut output. The audio stream received over USb will be sent to the speaker
+AnalogOut speaker(p18);
+
+// ticker to send data to the speaker at the good frequency
+Ticker tic;
+
+// buffer where will be store one audio packet
+uint8_t buf[LENGTH_AUDIO_PACKET];
+
+// show if an audio packet is available
+volatile bool available = false;
+
+// index of the value which will be send to the speaker
+int index_buf = 0;
+
+// previous value sent to the speaker
+uint16_t p_val = 0;
+
+// function executed each 1/FREQ s
+void tic_handler() {
+    float speaker_value;
+
+    if (available) {
+        //convert 2 bytes in float
+        speaker_value = (float)(*((int16_t *)&buf[index_buf]));
+        
+        // speaker_value between 0 and 65535
+        speaker_value += 32768.0;
+
+        // adjust according to current volume
+        speaker_value *= audio.getVolume();
+        
+        // as two bytes has been read, we move the index of two bytes
+        index_buf += 2;
+        
+        // if we have read all the buffer, no more data available
+        if (index_buf == LENGTH_AUDIO_PACKET) {
+            index_buf = 0;
+            available = false;
+        }
+    } else {
+        speaker_value = p_val;
+    }
+    
+    p_val = speaker_value;
+
+    // send value to the speaker
+    speaker.write_u16((uint16_t)speaker_value);
+}
+
+int main() {
+
+    // attach a function executed each 1/FREQ s
+    tic.attach_us(tic_handler, 1000000.0/(float)FREQ);
+
+    while (1) {
+        // read an audio packet
+        audio.read(buf);
+        available = true;
+    }
+}