Use usb audio alternate setting info

teensy3/usb_audio.cpp

 #define DMABUFATTR __attribute__ ((section(".dmabuffers"), aligned (4)))
 uint16_t usb_audio_receive_buffer[AUDIO_RX_SIZE/2] DMABUFATTR;
 uint32_t usb_audio_sync_feedback DMABUFATTR;
+uint8_t usb_audio_receive_setting=0;
 
 static uint32_t feedback_accumulator = 185042824;
 
 
 
 uint16_t usb_audio_transmit_buffer[AUDIO_TX_SIZE/2] DMABUFATTR;
+uint8_t usb_audio_transmit_setting=0;
 
 void AudioOutputUSB::begin(void)
 {
 
 	left = receiveReadOnly(0); // input 0 = left channel
 	right = receiveReadOnly(1); // input 1 = right channel
+	if (usb_audio_transmit_setting == 0) {
+		if (left) release(left);
+		if (right) release(right);
+		if (outgoing_count) {
+			if (left_1st) release(left_1st);
+			if (left_2nd) release(left_2nd);
+			if (right_1st) release(right_1st);
+			if (right_2nd) release(right_2nd);
+			outgoing_count = 0;
+			offset_1st = 0;
+		}
+		return;
+	}
 	if (left == NULL) {
 		if (right == NULL) return;
 		right->ref_count++;

teensy3/usb_audio.h

 extern void usb_audio_receive_callback(unsigned int len);
 extern unsigned int usb_audio_transmit_callback(void);
 extern uint32_t usb_audio_sync_feedback;
+extern uint8_t usb_audio_receive_setting;
+extern uint8_t usb_audio_transmit_setting;
 #ifdef __cplusplus
 }
 

teensy3/usb_dev.c

 #if defined(AUDIO_INTERFACE)
 	  case 0x0B01: // SET_INTERFACE (alternate setting)
 		if (setup.wIndex == AUDIO_INTERFACE+1) {
-			//audio_tx_alternate_setting = setup.wValue;
+			usb_audio_transmit_setting = setup.wValue;
 		} else if (setup.wIndex == AUDIO_INTERFACE+2) {
-			//audio_rx_alternate_setting = setup.wValue;
+			usb_audio_receive_setting = setup.wValue;
 		} else {
 			endpoint0_stall();
 			return;
 		datalen = 1;
 		data = reply_buffer;
 		if (setup.wIndex == AUDIO_INTERFACE+1) {
-			reply_buffer[0] = 0;
-			//reply_buffer[0] = audio_tx_alternate_setting;
+			reply_buffer[0] = usb_audio_transmit_setting;
 		} else if (setup.wIndex == AUDIO_INTERFACE+2) {
-			reply_buffer[0] = 0;
-			//reply_buffer[0] = audio_rx_alternate_setting;
+			reply_buffer[0] = usb_audio_receive_setting;
 		} else {
 			endpoint0_stall();
 			return;

teensy3/usb_dev.h

 extern uint16_t usb_audio_receive_buffer[];
 extern uint16_t usb_audio_transmit_buffer[];
 extern uint32_t usb_audio_sync_feedback;
+extern uint8_t usb_audio_receive_setting;
+extern uint8_t usb_audio_transmit_setting;
 extern void usb_audio_receive_callback(unsigned int len);
 extern unsigned int usb_audio_transmit_callback(void);
 #endif