USB_8 : audio loopback test at 16khz stereo 16bits

- Callback TX and RX interface is used.

Author: jamike

features/unsupported/tests/usb/device/audio_cb/main.cpp

@@ -0,0 +1,51 @@
+// Playback example with the USBAUDIO library
+
+#include "mbed.h"
+#include "USBAudio.h"
+
+// frequency: 48 kHz
+#define FREQ_SPK 16000
+#define FREQ_MIC 16000
+
+// 2channels: stereo
+#define NB_CHA_SPK 2
+#define NB_CHA_MIC 2
+
+// length computed: each ms, we receive 48 * 16bits ->48 * 2 bytes. as there are two channels, the length will be 48 * 2 * 2
+#define LENGTH_AUDIO_PACKET_SPK (FREQ_SPK / 500) * NB_CHA_SPK
+#define LENGTH_AUDIO_PACKET_MIC (FREQ_MIC / 500) * NB_CHA_MIC
+
+// USBAudio object
+USBAudio audio(FREQ_SPK, NB_CHA_SPK, FREQ_MIC, NB_CHA_MIC, 0xab45, 0x0378);
+int filled;
+int ready = 2;
+
+/*  buffer 4 packets to avoid  */
+int buf[4][LENGTH_AUDIO_PACKET_SPK/sizeof(int)];
+void tx_audio(void)
+{
+    /*  used some buffer in advance  */
+    ready = (filled+2)&0x3;
+    audio.writeSync((uint8_t *)buf[ready]);
+}
+
+
+void rx_audio(void)
+{
+    int size=0;
+    int next = (filled + 1)&0x3; 
+    size = audio.readSync((uint8_t *)buf[next]);
+    if (size ) filled = next;
+    if ((size) && (size!=LENGTH_AUDIO_PACKET_MIC)) printf("%d\n",size);
+}
+
+int main()
+{
+    filled = 0;
+    memset(&buf[0][0], 0, sizeof (buf));
+    audio.attachTx(tx_audio);
+    audio.attachRx(rx_audio);
+    /*  start the tx with a silent packet */
+    audio.write((uint8_t *)buf[2]);
+    while(1);
+}

tools/tests.py

@@ -1003,6 +1003,11 @@
         "source_dir": join(TEST_DIR, "usb", "device", "audio"),
         "dependencies": [MBED_LIBRARIES, USB_LIBRARIES],
     },
+    {
+        "id": "USB_8", "description": "AUDIO_CB",
+        "source_dir": join(TEST_DIR, "usb", "device", "audio_cb"),
+        "dependencies": [MBED_LIBRARIES, USB_LIBRARIES],
+    },
 
     # CMSIS DSP
     {