From c9e335daa88c932f9b09d49474ce25760a0d0884 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20J=C3=BCrges?= <jurges@astron.nl>
Date: Thu, 17 Jan 2019 17:04:48 +0000
Subject: [PATCH] SW-546: Add comments describing how the offset is calculated
---
RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc | 29 +++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)
diff --git a/RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc b/RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc
index 18235a010f9..b641d35930e 100644
--- a/RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc
+++ b/RTCP/Cobalt/OutputProc/src/TBB_Dipole.cc
@@ -316,14 +316,33 @@ namespace LOFAR
* first received frame.
*/
uint64_t offset = frame.header.time - itsDumpInfo.itsTime0;
- // Convert the offset in [s] to bytes. sampleFreq is in MHz.
+ /**
+ * Convert the offset in [s] to samples containing a complex numbers of
+ * two 16 bit integers. sampleFreq is in MHz.
+ */
offset *= (frame.header.sampleFreq * 1000000U);
/**
- * Divide the offset by the size of an FFT block. The result is an index
- * for the current data frame.
+ * Divide the offset, i.e. the number of samples by the size of an FFT
+ * block. The result is the index of the raw voltage sampling window
+ * (size 1024 values) that got fed into the FFT. This not a sample within
+ * the window but just a rough indicator which window we are in!
+ * [ 1024 ][ 1024 ][ 1024 ]
+ * ^
+ * | Start recording
+ * ^
+ * | Window number of the 0th TBB data frame
+ * ^
+ * | Window number of frame N
+ * This is also then the index of the TBB frame for this frequency because
+ * the begin of a voltage window is also the begin of a frequency window.
*/
offset /= SPECTRAL_TRANSFORM_SIZE;
+ /**
+ * Now try to figure out where in the raw voltage data window our spectral
+ * frame exactly begins.
+ */
+
/**
* NOTE:
* untested body: when can I have enough test data from a working
@@ -343,6 +362,10 @@ namespace LOFAR
* second:
* 1 extra slice fitted in that second
*/
+ /**
+ * TODO
+ * Is this still needed? Sander/Thomas need to look into this.
+ */
offset += 1;
// avoid duplicate offset compensation next
time0 += 1;
--
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