From 9c5b00e8cd05d3e484d6bbfbee351845598cd2ec Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Mon, 17 Feb 2025 08:05:36 +0100
Subject: Add tist_at_fct0 configuration

---
 doc/advanced.mux       |  3 +++
 src/DabMultiplexer.cpp | 12 +++++++++---
 src/DabMultiplexer.h   |  2 +-
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/doc/advanced.mux b/doc/advanced.mux
index 246f981..618a6b6 100644
--- a/doc/advanced.mux
+++ b/doc/advanced.mux
@@ -36,6 +36,9 @@ general {
     ; in seconds.
     ; tist_offset 0
 
+    ; Specify the TIST value for the frame with FCT==0, in microseconds
+    ; tist_at_fct0 768000
+
     ; The management server is a simple TCP server that can present
     ; statistics data (buffers, overruns, underruns, etc)
     ; which can then be graphed a tool like Munin
diff --git a/src/DabMultiplexer.cpp b/src/DabMultiplexer.cpp
index 095a835..a68f09a 100644
--- a/src/DabMultiplexer.cpp
+++ b/src/DabMultiplexer.cpp
@@ -46,7 +46,7 @@ static vector<string> split_pipe_separated_string(const std::string& s)
     return components;
 }
 
-uint64_t MuxTime::init()
+uint64_t MuxTime::init(uint32_t tist_at_fct0_us)
 {
     /* At startup, derive edi_time, TIST and CIF count such that there is
      * a consistency across mux restarts. Ensure edi_time and TIST represent
@@ -83,7 +83,12 @@ uint64_t MuxTime::init()
     int64_t offset_ms = chrono::duration_cast<chrono::milliseconds>(offset).count();
     offset_ms += 1000 * (t_now - m_edi_time);
 
-    m_timestamp = 0;
+    if (tist_at_fct0_us >= 1000000) {
+        etiLog.level(error) << "tist_at_fct0 may not be larger than 1s";
+        throw MuxInitException();
+    }
+
+    m_timestamp = (uint64_t)tist_at_fct0_us * 16384 / 1000;
     while (offset_ms >= 24) {
         increment_timestamp();
         currentFrame++;
@@ -177,7 +182,8 @@ void DabMultiplexer::prepare(bool require_tai_clock)
         throw MuxInitException();
     }
 
-    currentFrame = m_time.init();
+    const uint32_t tist_at_fct0_us = m_pt.get<double>("general.tist_at_fct0", 0);
+    currentFrame = m_time.init(tist_at_fct0_us);
     m_time.mnsc_increment_time = false;
 
     bool tist_enabled = m_pt.get("general.tist", false);
diff --git a/src/DabMultiplexer.h b/src/DabMultiplexer.h
index 92fa2c0..aa6adfb 100644
--- a/src/DabMultiplexer.h
+++ b/src/DabMultiplexer.h
@@ -67,7 +67,7 @@ class MuxTime {
     std::time_t mnsc_time = 0;
 
     /* Setup the time and return the initial currentFrame counter value */
-    uint64_t init();
+    uint64_t init(uint32_t tist_at_fct0_us);
     void increment_timestamp();
 };
 
-- 
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