From d19b4efa2e96ee793da7109a804e619254ea4649 Mon Sep 17 00:00:00 2001
From: Mike Walters <mike@flomp.net>
Date: Mon, 25 Jul 2016 22:57:13 +0100
Subject: [PATCH] Only transfer one block per re-tune

---
 firmware/hackrf_usb/usb_api_scan.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/firmware/hackrf_usb/usb_api_scan.c b/firmware/hackrf_usb/usb_api_scan.c
index 9b160dec..60e4b7c6 100644
--- a/firmware/hackrf_usb/usb_api_scan.c
+++ b/firmware/hackrf_usb/usb_api_scan.c
@@ -77,13 +77,14 @@ void scan_mode(void) {
 		if ( usb_bulk_buffer_offset >= 16384
 		     && phase == 1
 		     && transceiver_mode() != TRANSCEIVER_MODE_OFF) {
-			usb_transfer_schedule_block(
-				(transceiver_mode() == TRANSCEIVER_MODE_RX)
-				? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
-				&usb_bulk_buffer[0x0000],
-				0x4000,
-				NULL, NULL
-				);
+			if (blocks_queued == 2)
+				usb_transfer_schedule_block(
+					(transceiver_mode() == TRANSCEIVER_MODE_RX)
+					? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
+					&usb_bulk_buffer[0x0000],
+					0x4000,
+					NULL, NULL
+					);
 			phase = 0;
 			blocks_queued++;
 		}
@@ -92,13 +93,14 @@ void scan_mode(void) {
 		if ( usb_bulk_buffer_offset < 16384
 		     && phase == 0
 		     && transceiver_mode() != TRANSCEIVER_MODE_OFF) {
-			usb_transfer_schedule_block(
-				(transceiver_mode() == TRANSCEIVER_MODE_RX)
-				? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
-				&usb_bulk_buffer[0x4000],
-				0x4000,
-				NULL, NULL
-			);
+			if (blocks_queued == 2)
+				usb_transfer_schedule_block(
+					(transceiver_mode() == TRANSCEIVER_MODE_RX)
+					? &usb_endpoint_bulk_in : &usb_endpoint_bulk_out,
+					&usb_bulk_buffer[0x4000],
+					0x4000,
+					NULL, NULL
+				);
 			phase = 1;
 			blocks_queued++;
 		}