From 5e6e70659bf520af56d09053c88efecfc07ab072 Mon Sep 17 00:00:00 2001
From: Michael Ossmann <mike@ossmann.com>
Date: Wed, 8 Feb 2017 00:37:42 -0700
Subject: [PATCH] hackrf_sweep: suppress processing and output until the first
 expected frequency is seen

---
 host/hackrf-tools/src/hackrf_sweep.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/host/hackrf-tools/src/hackrf_sweep.c b/host/hackrf-tools/src/hackrf_sweep.c
index 40bdb6eb..de08f7e2 100644
--- a/host/hackrf-tools/src/hackrf_sweep.c
+++ b/host/hackrf-tools/src/hackrf_sweep.c
@@ -173,6 +173,7 @@ bool antenna = false;
 uint32_t antenna_enable;
 
 bool binary_output = false;
+volatile bool sweep_started = false;
 
 int fftSize = 20;
 uint32_t fft_bin_width;
@@ -216,6 +217,14 @@ int rx_callback(hackrf_transfer* transfer) {
 			buf += SAMPLES_PER_BLOCK;
 			break;
 		}
+		if(!sweep_started) {
+			if (frequency == (uint64_t)(FREQ_ONE_MHZ*frequencies[0])) {
+				sweep_started = true;
+			} else {
+				buf += SAMPLES_PER_BLOCK;
+				continue;
+			}
+		}
 		if((FREQ_MAX_MHZ * FREQ_ONE_MHZ) < frequency) {
 			buf += SAMPLES_PER_BLOCK;
 			break;