USB audio on Teensy 4.0 (even yet more still work in progress)

teensy4/usb_audio.cpp

 
 extern volatile uint8_t usb_high_speed;
 static void rx_event(transfer_t *t);
+static void rx_queue_transfer(void);
 
-static transfer_t rx_transfer __attribute__ ((used, aligned(32)));
+/*static*/ transfer_t rx_transfer __attribute__ ((used, aligned(32)));
+/*static*/ transfer_t sync_transfer __attribute__ ((used, aligned(32)));
 DMAMEM static uint8_t rx_buffer[AUDIO_RX_SIZE] __attribute__ ((aligned(32)));
-
-//#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;
+DMAMEM uint32_t usb_audio_sync_feedback;
 
 uint8_t usb_audio_receive_setting=0;
 uint8_t usb_audio_transmit_setting=0;
+uint8_t usb_audio_sync_nbytes;
+uint8_t usb_audio_sync_rshift;
+
+uint32_t feedback_accumulator;
 
-static uint32_t feedback_accumulator = 185042824;
+volatile uint32_t usb_audio_underrun_count;
+volatile uint32_t usb_audio_overrun_count;
 
 
-static void rx_queue_transfer(void)
+static void rx_event(transfer_t *t)
 {
+	if (t) {
+		int len = AUDIO_RX_SIZE - ((rx_transfer.status >> 16) & 0x7FFF);
+		//printf("rx %u\n", len);
+		usb_audio_receive_callback(len);
+	}
 	usb_prepare_transfer(&rx_transfer, rx_buffer, AUDIO_RX_SIZE, 0);
-	arm_dcache_delete(&rx_transfer, AUDIO_RX_SIZE);
+	arm_dcache_delete(&rx_buffer, AUDIO_RX_SIZE);
 	usb_receive(AUDIO_RX_ENDPOINT, &rx_transfer);
 }
 
+static void sync_event(transfer_t *t)
+{
+	// USB 2.0 Specification, 5.12.4.2 Feedback, pages 73-75
+	//printf("sync %x\n", sync_transfer.status); // too slow, can't print this much
+	usb_audio_sync_feedback = feedback_accumulator >> usb_audio_sync_rshift;
+	usb_prepare_transfer(&sync_transfer, &usb_audio_sync_feedback, usb_audio_sync_nbytes, 0);
+	arm_dcache_delete(&usb_audio_sync_feedback, usb_audio_sync_nbytes);
+	usb_transmit(AUDIO_SYNC_ENDPOINT, &sync_transfer);
+}
+
 void usb_audio_configure(void)
 {
 	printf("usb_audio_configure\n");
+	usb_audio_underrun_count = 0;
+	usb_audio_overrun_count = 0;
+	feedback_accumulator = 739875226; // 44.1 * 2^24
+	if (usb_high_speed) {
+		usb_audio_sync_nbytes = 4;
+		usb_audio_sync_rshift = 8;
+	} else {
+		usb_audio_sync_nbytes = 3;
+		usb_audio_sync_rshift = 10;
+	}
 	memset(&rx_transfer, 0, sizeof(rx_transfer));
 	usb_config_rx_iso(AUDIO_RX_ENDPOINT, AUDIO_RX_SIZE, 1, rx_event);
-	rx_queue_transfer();
+	//rx_queue_transfer();
+	rx_event(NULL);
+	memset(&sync_transfer, 0, sizeof(sync_transfer));
+	usb_config_tx_iso(AUDIO_SYNC_ENDPOINT, usb_audio_sync_nbytes, 1, sync_event);
+	sync_event(NULL);
 }
 
 void AudioInputUSB::begin(void)
 	// but also because the PC may stop transmitting data, which
 	// means we no longer get receive callbacks from usb.c
 	update_responsibility = false;
-	//usb_audio_sync_feedback = feedback_accumulator >> 8;
 }
 
 static void copy_to_buffers(const uint32_t *src, int16_t *left, int16_t *right, unsigned int len)
 // Called from the USB interrupt when an isochronous packet arrives
 // we must completely remove it from the receive buffer before returning
 //
-static void rx_event(transfer_t *t)
-{
-	unsigned int len = AUDIO_RX_SIZE - ((t->status >> 16) & 0x7FFF);
-	//int len = AUDIO_RX_SIZE - ((rx_transfer.status >> 16) & 0x7FFF);
-	printf("rx %u\n", len);
-	// TODO: actually move the data from USB to audio lib
-	usb_audio_receive_callback(len);
-	rx_queue_transfer();
-}
-
 #if 1
 void usb_audio_receive_callback(unsigned int len)
 {
 			if (AudioInputUSB::ready_left || AudioInputUSB::ready_right) {
 				// buffer overrun, PC sending too fast
 				AudioInputUSB::incoming_count = count + avail;
-				//if (len > 0) {
-					//serial_print("!");
+				if (len > 0) {
+					usb_audio_overrun_count++;
+					printf("!");
 					//serial_phex(len);
-				//}
+				}
 				return;
 			}
 			send:
 	__enable_irq();
 	if (f) {
 		int diff = AUDIO_BLOCK_SAMPLES/2 - (int)c;
-		feedback_accumulator += diff / 3;
-		uint32_t feedback = (feedback_accumulator >> 8) + diff * 100;
-#ifdef MACOSX_ADAPTIVE_LIMIT
-		if (feedback > 722698) feedback = 722698;
-#endif
+		feedback_accumulator += diff * 2;
+
+		 //__disable_irq();
+		 //printf("fb:%x\n", feedback_accumulator);
+		 //__enable_irq();
+		//uint32_t feedback = (feedback_accumulator >> 8) + diff * 100;
 		//usb_audio_sync_feedback = feedback;
 		//if (diff > 0) {
 			//serial_print(".");
 	//serial_phex(c);
 	//serial_print(".");
 	if (!left || !right) {
-		//serial_print("#"); // buffer underrun - PC sending too slow
+		usb_audio_underrun_count++;
+		printf("#"); // buffer underrun - PC sending too slow
 		//if (f) feedback_accumulator += 10 << 8;
 	}
 	if (left) {

teensy4/usb_desc.c

 	0x11, 					// bmAttributes = isochronous, feedback
 	4, 0,					// wMaxPacketSize, 4 bytes
 	4,			 		// bInterval, 4 = 4 = every 8 micro-frames
-	5,					// bRefresh, 5 = 32ms
+	7,					// bRefresh,
 	0,					// bSynchAddress
 #endif