From f24699f14eaccc850562756a7d98322ab998fc64 Mon Sep 17 00:00:00 2001
From: Silvano Seva <silseva@fastwebnet.it>
Date: Wed, 19 Oct 2022 08:29:53 +0200
Subject: [PATCH] Fixed bug in M17 demodulator causing it to sometimes take
 more than 20ms to process a block of baseband samples when, in unlocked
 state, a valid syncword is searched.

---
 openrtx/src/protocols/M17/M17Demodulator.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/openrtx/src/protocols/M17/M17Demodulator.cpp b/openrtx/src/protocols/M17/M17Demodulator.cpp
index 66b839d5..61df2c79 100644
--- a/openrtx/src/protocols/M17/M17Demodulator.cpp
+++ b/openrtx/src/protocols/M17/M17Demodulator.cpp
@@ -523,10 +523,15 @@ bool M17Demodulator::update()
 
                     if ((hammingSync > maxHamming) && (hammingLsf > maxHamming))
                     {
-                        // Lock lost
+                        // Lock lost, reset demodulator alignment (phase) only
+                        // if we were locked on a valid signal.
+                        // This to avoid, in case of absence of carrier, to fall
+                        // in a loop where the demodulator continues to search
+                        // for the syncword in the same block of samples, causing
+                        // the update function to take more than 20ms to complete.
+                        if(locked) phase = 0;
                         syncDetected = false;
                         locked       = false;
-                        phase        = 0;
 
                         #ifdef ENABLE_DEMOD_LOG
                         // Pre-arm the log trigger.