From 98fbb5ae2835160fe89946e4117c2aeee2b578f3 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 21 Apr 2026 19:55:46 +0000
Subject: [PATCH] Optimize USRP TX tail zeroing for partial interpolation fills

Agent-Logs-Url: https://github.com/srcejon/sdrangel/sessions/bafbe6fb-a6ec-4ee0-92f8-caa27da815f5

Co-authored-by: srcejon <57259258+srcejon@users.noreply.github.com>
---
 plugins/samplesink/usrpoutput/usrpoutputthread.cpp | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/plugins/samplesink/usrpoutput/usrpoutputthread.cpp b/plugins/samplesink/usrpoutput/usrpoutputthread.cpp
index 9dd536692..c8209c75c 100644
--- a/plugins/samplesink/usrpoutput/usrpoutputthread.cpp
+++ b/plugins/samplesink/usrpoutput/usrpoutputthread.cpp
@@ -123,10 +123,6 @@ void USRPOutputThread::run()
 //  Interpolate according to specified log2 (ex: log2=4 => decim=16)
 void USRPOutputThread::callback(qint16* buf, qint32 len)
 {
-    // Fill any sample tail not overwritten by interpolation (for non power-of-two streamer block sizes)
-    // so stale data is never transmitted.
-    std::fill(buf, buf + (2 * len), 0);
-
     SampleVector& data = m_sampleFifo->getData();
     unsigned int iPart1Begin, iPart1End, iPart2Begin, iPart2End;
     m_sampleFifo->read(len/(1<<m_log2Interp), iPart1Begin, iPart1End, iPart2Begin, iPart2End);
@@ -140,6 +136,14 @@ void USRPOutputThread::callback(qint16* buf, qint32 len)
     if (iPart2Begin != iPart2End) {
         callbackPart(buf + 2*shift, data, iPart2Begin, iPart2End);
     }
+
+    const unsigned int writtenSamples =
+            ((iPart1End - iPart1Begin) + (iPart2End - iPart2Begin)) * (1U << m_log2Interp);
+
+    if (writtenSamples < static_cast<unsigned int>(len))
+    {
+        std::fill(buf + 2*writtenSamples, buf + 2*len, 0);
+    }
 }
 
 void USRPOutputThread::callbackPart(qint16* buf, SampleVector& data, unsigned int iBegin, unsigned int iEnd)