Samuel Mokrani
USBAudio speaker example
Revision 0:5176b3dfccd6, committed 2011-11-30
- Comitter:
- samux
- Date:
- Wed Nov 30 09:51:59 2011 +0000
- Child:
- 1:0335b5c18618
- Commit message:
Changed in this revision
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/USBDevice.lib Wed Nov 30 09:51:59 2011 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/samux/code/USBDevice/#181abc5c9bf5
--- /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;
+ }
+}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Wed Nov 30 09:51:59 2011 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/7110ebee3484